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Fresh lava from Fagradalsfjall volcano eruption in Iceland, 2023

Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C (1,470 to 2,190 °F). Lava may be erupted directly onto the land surface or onto the sea floor or it may be ejected into the atmosphere before falling back down. The solid volcanic rock resulting from subsequent cooling of the molten material is often also called lava.

A lava flow is an outpouring of lava during an effusive eruption. (An explosive eruption, by contrast, produces a mixture of volcanic ash and other fragments called tephra, not lava flows.) The viscosity of most molten lava is about that of ketchup, roughly 10,000 to 100,000 times that of water (the latter two substances measured at 25 °C (77 °F) and 1 atm). Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops a solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing.[1]

Etymology

[edit]

The word lava comes from Italian and is probably derived from the Latin word labes, which means a 'fall' or 'slide'.[2][3] An early use of the word in connection with extrusion of magma from below the surface is found in a short account of the 1737 eruption of Vesuvius, written by Francesco Serao, who described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano (a lahar) after heavy rain.[4][5]

Properties of lava

[edit]

Composition

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Video of lava agitating and bubbling in the volcano eruption of Litli-Hrútur, 2023

Solidified lava on the Earth's crust is predominantly silicate minerals: mostly feldspars, feldspathoids, olivine, pyroxenes, amphiboles, micas and quartz.[6] Rare nonsilicate lavas can be formed by local melting of nonsilicate mineral deposits[7] or by separation of a magma into immiscible silicate and nonsilicate liquid phases.[8]

Silicate lavas

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Silicate lavas are molten mixtures dominated by oxygen and silicon, the most abundant elements of the Earth's crust, with smaller quantities of aluminium, calcium, magnesium, iron, sodium, and potassium and minor amounts of many other elements.[6] Petrologists routinely express the composition of a silicate lava in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the lava.[9]

The silica component dominates the physical behavior of silicate magmas. Silicon ions in lava strongly bind to four oxygen ions in a tetrahedral arrangement. If an oxygen ion is bound to two silicon ions in the melt, it is described as a bridging oxygen, and lava with many clumps or chains of silicon ions connected by bridging oxygen ions is described as partially polymerized. Aluminium in combination with alkali metal oxides (sodium and potassium) also tends to polymerize the lava.[10] Other cations, such as ferrous iron, calcium, and magnesium, bond much more weakly to oxygen and reduce the tendency to polymerize.[11] Partial polymerization makes the lava viscous, so lava high in silica is much more viscous than lava low in silica.[10]

Because of the role of silica in determining viscosity and because many other properties of a lava (such as its temperature) are observed to correlate with silica content, silicate lavas are divided into four chemical types based on silica content: felsic, intermediate, mafic, and ultramafic.[12]

Felsic lava
[edit]

Felsic or silicic lavas have a silica content greater than 63%. They include rhyolite and dacite lavas. With such a high silica content, these lavas are extremely viscous, ranging from 108 cP (105 Pa⋅s) for hot rhyolite lava at 1,200 °C (2,190 °F) to 1011 cP (108 Pa⋅s) for cool rhyolite lava at 800 °C (1,470 °F).[13] For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines, lava domes or "coulees" (which are thick, short lava flows).[14] The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian.[15]

Felsic magmas can erupt at temperatures as low as 800 °C (1,470 °F).[16] Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States.[17]

Intermediate lava
[edit]

Intermediate or andesitic lavas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic lavas. Intermediate lavas form andesite domes and block lavas and may occur on steep composite volcanoes, such as in the Andes.[18] They are also commonly hotter than felsic lavas, in the range of 850 to 1,100 °C (1,560 to 2,010 °F). Because of their lower silica content and higher eruptive temperatures, they tend to be much less viscous, with a typical viscosity of 3.5 million cP (3,500 Pa⋅s) at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter.[19] Intermediate lavas show a greater tendency to form phenocrysts.[20] Higher iron and magnesium tends to manifest as a darker groundmass, including amphibole or pyroxene phenocrysts.[21]

Mafic lava
[edit]

Mafic or basaltic lavas are typified by relatively high magnesium oxide and iron oxide content (whose molecular formulas provide the consonants in mafic) and have a silica content limited to a range of 52% to 45%. They generally erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F) and at relatively low viscosities, around 104 to 105 cP (10 to 100 Pa⋅s). This is similar to the viscosity of ketchup,[22] although it is still many orders of magnitude higher than that of water. Mafic lavas tend to produce low-profile shield volcanoes or flood basalts, because the less viscous lava can flow for long distances from the vent. The thickness of a solidified basaltic lava flow, particularly on a low slope, may be much greater than the thickness of the moving molten lava flow at any one time, because basaltic lavas may "inflate" by a continued supply of lava and its pressure on a solidified crust.[23] Most basaltic lavas are of ʻaʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas, which are rather similar to entrail-type pahoehoe lavas on land.[24]

Ultramafic lava
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Ultramafic lavas, such as komatiite and highly magnesian magmas that form boninite, take the composition and temperatures of eruptions to the extreme. All have a silica content under 45%. Komatiites contain over 18% magnesium oxide and are thought to have erupted at temperatures of 1,600 °C (2,910 °F). At this temperature there is practically no polymerization of the mineral compounds, creating a highly mobile liquid.[25] Viscosities of komatiite magmas are thought to have been as low as 100 to 1000 cP (0.1 to 1 Pa⋅s), similar to that of light motor oil.[13] Most ultramafic lavas are no younger than the Proterozoic, with a few ultramafic magmas known from the Phanerozoic in Central America that are attributed to a hot mantle plume. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas.[26]

Alkaline lavas
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Some silicate lavas have an elevated content of alkali metal oxides (sodium and potassium), particularly in regions of continental rifting, areas overlying deeply subducted plates, or at intraplate hotspots.[27] Their silica content can range from ultramafic (nephelinites, basanites and tephrites) to felsic (trachytes). They are more likely to be generated at greater depths in the mantle than subalkaline magmas.[28] Olivine nephelinite lavas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other lavas.[29]

Examples of lava compositions (wt%)[30]
Component Nephelinite Tholeiitic picrite Tholeiitic basalt Andesite Rhyolite
SiO2 39.7 46.4 53.8 60.0 73.2
TiO2 2.8 2.0 2.0 1.0 0.2
Al2O3 11.4 8.5 13.9 16.0 14.0
Fe2O3 5.3 2.5 2.6 1.9 0.6
FeO 8.2 9.8 9.3 6.2 1.7
MnO 0.2 0.2 0.2 0.2 0.0
MgO 12.1 20.8 4.1 3.9 0.4
CaO 12.8 7.4 7.9 5.9 1.3
Na2O 3.8 1.6 3.0 3.9 3.9
K2O 1.2 0.3 1.5 0.9 4.1
P2O5 0.9 0.2 0.4 0.2 0.0
Tholeiitic basalt lava
  1. SiO2 (53.8%)
  2. Al2O3 (13.9%)
  3. FeO (9.30%)
  4. CaO (7.90%)
  5. MgO (4.10%)
  6. Na2O (3.00%)
  7. Fe2O3 (2.60%)
  8. TiO2 (2.00%)
  9. K2O (1.50%)
  10. P2O5 (0.40%)
  11. MnO (0.20%)
Rhyolite lava
  1. SiO2 (73.2%)
  2. Al2O3 (14.0%)
  3. FeO (1.70%)
  4. CaO (1.30%)
  5. MgO (0.40%)
  6. Na2O (3.90%)
  7. Fe2O3 (0.60%)
  8. TiO2 (0.20%)
  9. K2O (4.10%)
  10. P2O5 (0.00%)
  11. MnO (0.00%)

Non-silicate lavas

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Some lavas of unusual composition have erupted onto the surface of the Earth. These include:

  • Carbonatite and natrocarbonatite lavas are known from Ol Doinyo Lengai volcano in Tanzania, which is the sole example of an active carbonatite volcano.[31] Carbonatites in the geologic record are typically 75% carbonate minerals, with lesser amounts of silica-undersaturated silicate minerals (such as micas and olivine), apatite, magnetite, and pyrochlore. This may not reflect the original composition of the lava, which may have included sodium carbonate that was subsequently removed by hydrothermal activity, though laboratory experiments show that a calcite-rich magma is possible. Carbonatite lavas show stable isotope ratios indicating they are derived from the highly alkaline silicic lavas with which they are always associated, probably by separation of an immiscible phase.[32] Natrocarbonatite lavas of Ol Doinyo Lengai are composed mostly of sodium carbonate, with about half as much calcium carbonate and half again as much potassium carbonate, and minor amounts of halides, fluorides, and sulphates. The lavas are extremely fluid, with viscosities only slightly greater than water, and are very cool, with measured temperatures of 491 to 544 °C (916 to 1,011 °F).[33]
  • Iron oxide lavas are thought to be the source of the iron ore at Kiruna, Sweden which formed during the Proterozoic.[8] Iron oxide lavas of Pliocene age occur at the El Laco volcanic complex on the Chile-Argentina border.[7] Iron oxide lavas are thought to be the result of immiscible separation of iron oxide magma from a parental magma of calc-alkaline or alkaline composition.[8]
  • Sulfur lava flows up to 250 metres (820 feet) long and 10 metres (33 feet) wide occur at Lastarria volcano, Chile. They were formed by the melting of sulfur deposits at temperatures as low as 113 °C (235 °F).[7]

The term "lava" can also be used to refer to molten "ice mixtures" in eruptions on the icy satellites of the Solar System's giant planets.[34]

Rheology

[edit]
Toes of a pāhoehoe advance across a road in Kalapana on the east rift zone of Kīlauea Volcano in Hawaii, United States

The lava's viscosity mostly determines the behavior of lava flows. While the temperature of common silicate lava ranges from about 800 °C (1,470 °F) for felsic lavas to 1,200 °C (2,190 °F) for mafic lavas,[16] its viscosity ranges over seven orders of magnitude, from 1011 cP (108 Pa⋅s) for felsic lavas to 104 cP (10 Pa⋅s) for mafic lavas.[16] Lava viscosity is mostly determined by composition but also depends on temperature[13] and shear rate.[35]

Lava viscosity determines the kind of volcanic activity that takes place when the lava is erupted. The greater the viscosity, the greater the tendency for eruptions to be explosive rather than effusive. As a result, most lava flows on Earth, Mars, and Venus are composed of basalt lava.[36] On Earth, 90% of lava flows are mafic or ultramafic, with intermediate lava making up 8% of flows and felsic lava making up just 2% of flows.[37] Viscosity also determines the aspect (thickness relative to lateral extent) of flows, the speed with which flows move, and the surface character of the flows.[13][38]

When highly viscous lavas erupt effusively rather than in their more common explosive form, they almost always erupt as high-aspect flows or domes. These flows take the form of block lava rather than ʻaʻā or pāhoehoe. Obsidian flows are common.[39] Intermediate lavas tend to form steep stratovolcanoes, with alternating beds of lava from effusive eruptions and tephra from explosive eruptions.[40] Mafic lavas form relatively thin flows that can move great distances, forming shield volcanoes with gentle slopes.[41]

In addition to melted rock, most lavas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths, and fragments of previously solidified lava. The crystal content of most lavas gives them thixotropic and shear thinning properties.[42] In other words, most lavas do not behave like Newtonian fluids, in which the rate of flow is proportional to the shear stress. Instead, a typical lava is a Bingham fluid, which shows considerable resistance to flow until a stress threshold, called the yield stress, is crossed.[43] This results in plug flow of partially crystalline lava. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear is concentrated in a thin layer in the toothpaste next to the tube and only there does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the lava.[44] Once the crystal content reaches about 60%, the lava ceases to behave like a fluid and begins to behave like a solid. Such a mixture of crystals with melted rock is sometimes described as crystal mush.[45]

Lava flow speeds vary based primarily on viscosity and slope. In general, lava flows slowly, with typical speeds for Hawaiian basaltic flows of 0.40 km/h (0.25 mph) and maximum speeds of 10 to 48 km/h (6 to 30 mph) on steep slopes.[37] An exceptional speed of 32 to 97 km/h (20 to 60 mph) was recorded following the collapse of a lava lake at Mount Nyiragongo.[37] The scaling relationship for lavas is that the average speed of a flow scales as the square of its thickness divided by its viscosity.[46] This implies that a rhyolite flow would have to be about a thousand times thicker than a basalt flow to flow at a similar speed.

Temperature

[edit]
Columnar jointing in Giant's Causeway in Northern Ireland

The temperature of most types of molten lava ranges from about 800 °C (1,470 °F) to 1,200 °C (2,190 °F)[16] depending on the lava's chemical composition. This temperature range is similar to the hottest temperatures achievable with a forced air charcoal forge.[47] Lava is most fluid when first erupted, becoming much more viscous as its temperature drops.[13]

Lava flows quickly develop an insulating crust of solid rock as a result of radiative loss of heat. Thereafter, the lava cools by a very slow conduction of heat through the rocky crust. For instance, geologists of the United States Geological Survey regularly drilled into the Kilauea Iki lava lake, formed in an eruption in 1959. After three years, the solid surface crust, whose base was at a temperature of 1,065 °C (1,949 °F), was still only 14 m (46 ft) thick, even though the lake was about 100 m (330 ft) deep. Residual liquid was still present at depths of around 80 m (260 ft) nineteen years after the eruption.[16]

A cooling lava flow shrinks, and this fractures the flow. Basalt flows show a characteristic pattern of fractures. The uppermost parts of the flow show irregular downward-splaying fractures, while the lower part of the flow shows a very regular pattern of fractures that break the flow into five- or six-sided columns. The irregular upper part of the solidified flow is called the entablature, while the lower part that shows columnar jointing is called the colonnade. (The terms are borrowed from Greek temple architecture.) Likewise, regular vertical patterns on the sides of columns, produced by cooling with periodic fracturing, are described as chisel marks. Despite their names, these are natural features produced by cooling, thermal contraction, and fracturing.[48]

As lava cools, crystallizing inwards from its edges, it expels gases to form vesicles at the lower and upper boundaries. These are described as pipe-stem vesicles or pipe-stem amygdales. Liquids expelled from the cooling crystal mush rise upwards into the still-fluid center of the cooling flow and produce vertical vesicle cylinders. Where these merge towards the top of the flow, they form sheets of vesicular basalt and are sometimes capped with gas cavities that sometimes fill with secondary minerals. The beautiful amethyst geodes found in the flood basalts of South America formed in this manner.[49]

Flood basalts typically crystallize little before they cease flowing, and, as a result, flow textures are uncommon in less silicic flows.[50] On the other hand, flow banding is common in felsic flows.[51]

Lava morphology

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Lava entering the sea to expand the big island of Hawaii, Hawaiʻi Volcanoes National Park

The morphology of lava describes its surface form or texture. More fluid basaltic lava flows tend to form flat sheet-like bodies, whereas viscous rhyolite lava flows form knobbly, blocky masses of rock. Lava erupted underwater has its own distinctive characteristics.

Lava enters the Pacific at the Big Island of Hawaii.

ʻAʻā

[edit]
The following subsection is about the types of lava flow. For the sculpture of a god from the Pacific island of Rurutu, see Statue of A'a from Rurutu.
Glowing ʻaʻā flow front advancing over pāhoehoe on the coastal plain of Kīlauea in Hawaii, United States

ʻAʻā (also spelled aa, aʻa, ʻaʻa, and a-aa, and pronounced [ʔəˈʔaː] or /ˈɑː(ʔ)ɑː/) is one of three basic types of flow lava. ʻAʻā is basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker. The word is Hawaiian meaning "stony rough lava", but also to "burn" or "blaze";[52] it was introduced as a technical term in geology by Clarence Dutton.[53][54]

The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an ʻaʻā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an ʻaʻā flow.[55]

Accretionary lava balls as large as 3 metres (10 feet) are common on ʻaʻā flows.[56] ʻAʻā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into ʻaʻā if it becomes turbulent from meeting impediments or steep slopes.[55]

The sharp, angled texture makes ʻaʻā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on Magellan pictures).[57]

ʻAʻā lavas typically erupt at temperatures of 1,050 to 1,150 °C (1,920 to 2,100 °F) or greater.[58][59]

Pāhoehoe

[edit]
Pāhoehoe lava from Kīlauea volcano, Hawaii, United States

Pāhoehoe (also spelled pahoehoe, from Hawaiian [paːˈhoweˈhowe][60] meaning "smooth, unbroken lava") is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. The Hawaiian word was introduced as a technical term in geology by Clarence Dutton.[53][54]

A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms lava tubes where the minimal heat loss maintains a low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into ʻaʻā flows in response to heat loss and consequent increase in viscosity.[24] Experiments suggest that the transition takes place at a temperature between 1,200 and 1,170 °C (2,190 and 2,140 °F), with some dependence on shear rate.[61][35] Pahoehoe lavas typically have a temperature of 1,100 to 1,200 °C (2,010 to 2,190 °F).[16]

On the Earth, most lava flows are less than 10 km (6.2 mi) long, but some pāhoehoe flows are more than 50 km (31 mi) long.[62] Some flood basalt flows in the geologic record extend for hundreds of kilometres.[63]

The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on Magellan picture).[57]

Block lava flows

[edit]
Block lava at Fantastic Lava Beds near Cinder Cone in Lassen Volcanic National Park

Block lava flows are typical of andesitic lavas from stratovolcanoes. They behave in a similar manner to ʻaʻā flows but their more viscous nature causes the surface to be covered in smooth-sided angular fragments (blocks) of solidified lava instead of clinkers. As with ʻaʻā flows, the molten interior of the flow, which is kept insulated by the solidified blocky surface, advances over the rubble that falls off the flow front. They also move much more slowly downhill and are thicker in depth than ʻaʻā flows. [15]

Pillow lava

[edit]
Main article: Pillow lava
Pillow lava on the ocean floor near Hawaii

Pillow lava is the lava structure typically formed when lava emerges from an underwater volcanic vent or subglacial volcano or a lava flow enters the ocean. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since water covers the majority of Earth's surface and most volcanoes are situated near or under bodies of water, pillow lava is very common.[64]

Lava landforms

[edit]

Because it is formed from viscous molten rock, lava flows and eruptions create distinctive formations, landforms and topographical features from the macroscopic to the microscopic.

Volcanoes

[edit]
Main article: Volcano
Arenal Volcano, Costa Rica, is a stratovolcano.

Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from shield volcanoes with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas.[65]

A caldera, which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards.[66] Such features may include volcanic crater lakes and lava domes after the event.[67] However, calderas can also form by non-explosive means such as gradual magma subsidence. This is typical of many shield volcanoes.[68]

Cinder and spatter cones

[edit]
Main article: Volcanic cone

Cinder cones and spatter cones are small-scale features formed by lava accumulation around a small vent on a volcanic edifice. Cinder cones are formed from tephra or ash and tuff which is thrown from an explosive vent. Spatter cones are formed by accumulation of molten volcanic slag and cinders ejected in a more liquid form.[69]

Kīpukas

[edit]
Main article: Kīpuka

Another Hawaiian English term derived from the Hawaiian language, a kīpuka denotes an elevated area such as a hill, ridge or old lava dome inside or downslope from an area of active volcanism. New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow.[70]

Lava domes and coulées

[edit]
Main article: Lava dome
A forested lava dome in the midst of the Valle Grande, the largest meadow in the Valles Caldera National Preserve, New Mexico, United States

Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera. As a volcano extrudes silicic lava, it can form an inflation dome or endogenous dome, gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, breccia and ash.[71]

Examples of lava dome eruptions include the Novarupta dome, and successive lava domes of Mount St Helens.[72]

When a dome forms on an inclined surface it can flow in short thick flows called coulées (dome flows). These flows often travel only a few kilometres from the vent.[39]

Lava tubes

[edit]
Main article: Lava tube

Lava tubes are formed when a flow of relatively fluid lava cools on the upper surface sufficiently to form a crust. Beneath this crust, which being made of rock is an excellent insulator, the lava can continue to flow as a liquid. When this flow occurs over a prolonged period of time the lava conduit can form a tunnel-like aperture or lava tube, which can conduct molten rock many kilometres from the vent without cooling appreciably. Often these lava tubes drain out once the supply of fresh lava has stopped, leaving a considerable length of open tunnel within the lava flow.[73]

Lava tubes are known from the modern day eruptions of Kīlauea,[74] and significant, extensive and open lava tubes of Tertiary age are known from North Queensland, Australia, some extending for 15 kilometres (9 miles).[75]

Lava lakes

[edit]
Main article: Lava lake
Shiprock, New Mexico, United States: a volcanic neck in the distance, with a radiating dike on its south side

Rarely, a volcanic cone may fill with lava but not erupt. Lava which pools within the caldera is known as a lava lake.[76] Lava lakes do not usually persist for long, either draining back into the magma chamber once pressure is relieved (usually by venting of gases through the caldera), or by draining via eruption of lava flows or pyroclastic explosion.

There are only a few sites in the world where permanent lakes of lava exist. These include:

Lava delta

[edit]
Main article: Lava delta

Lava deltas form wherever sub-aerial flows of lava enter standing bodies of water. The lava cools and breaks up as it encounters the water, with the resulting fragments filling in the seabed topography such that the sub-aerial flow can move further offshore. Lava deltas are generally associated with large-scale, effusive type basaltic volcanism.[80]

Lava fountains

[edit]
Lava fountain at Kīlauea

A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. The highest lava fountain recorded was during the 23 November 2013 eruption of Mount Etna in Italy, which reached a stable height of around 2,500 m (8,200 ft) for 18 minutes, briefly peaking at a height of 3,400 m (11,000 ft).[81] Lava fountains may occur as a series of short pulses, or a continuous jet of lava. They are commonly associated with Hawaiian eruptions.[82]

Hazards

[edit]

Lava flows are enormously destructive to property in their path. However, casualties are rare since flows are usually slow enough for people and animals to escape, though this is dependent on the viscosity of the lava. Nevertheless, injuries and deaths have occurred, either because they had their escape route cut off, because they got too close to the flow[83] or, more rarely, if the lava flow front travels too quickly. This notably happened during the eruption of Nyiragongo in Zaire (now Democratic Republic of the Congo). On the night of 10 January 1977, a crater wall was breached and a fluid lava lake drained out in under an hour. The resulting flow sped down the steep slopes at up to 100 km/h (62 mph), and overwhelmed several villages while residents were asleep. As a result of this disaster, the mountain was designated a Decade Volcano in 1991.[84]

Deaths attributed to volcanoes frequently have a different cause. For example, volcanic ejecta, pyroclastic flow from a collapsing lava dome, lahars, poisonous gases that travel ahead of lava, or explosions caused when the flow comes into contact with water.[83] A particularly dangerous area is called a lava bench. This very young ground will typically break off and fall into the sea.

Areas of recent lava flows continue to represent a hazard long after the lava has cooled. Where young flows have created new lands, land is more unstable and can break off into the sea. Flows often crack deeply, forming dangerous chasms, and a fall against ʻaʻā lava is similar to falling against broken glass. Rugged hiking boots, long pants, and gloves are recommended when crossing lava flows.

Diverting a lava flow is extremely difficult, but it can be accomplished in some circumstances, as was once partially achieved in Vestmannaeyjar, Iceland.[85] The optimal design of simple, low-cost barriers that divert lava flows is an area of ongoing research.[86][87]

Towns destroyed by lava flows

[edit]
Lava can easily destroy entire towns. This picture shows one of over 100 houses destroyed by the lava flow in Kalapana, Hawaii, United States, in 1990.

Towns damaged by lava flows

[edit]

Towns destroyed by tephra

[edit]

Tephra is lava in the form of volcanic ash, lapilli, volcanic bombs or volcanic blocks.

See also

[edit]
  • Blue lava – Optical phenomenon resulting from burning sulfur
  • Lava planet – Terrestrial planet with the surface covered by molten lava
  • Laze (geology) – Acid haze formed when molten lava enters the cold ocean
  • Vog – Air pollution resulting from volcanic gases reacting with the atmosphere

References

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Lava

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Lava is molten rock that erupts onto the Earth's surface through volcanic vents or fissures, distinguishing it from , which is the same material but remains underground. Upon reaching the surface, lava flows under the influence of gravity, varying in behavior based on its composition, , and , before cooling and solidifying into igneous rocks such as or . This process forms extensive landscapes, including shield volcanoes and lava plateaus, and poses significant hazards due to its ability to bury, ignite, or overrun structures and ecosystems in its path. The term "lava" originates from the Italian word meaning "stream" or "torrent," derived from the Latin "lavare," meaning "to wash," alluding to its flowing nature. The composition of lava primarily depends on its silica content, which influences its fluidity and eruption style; basaltic lava, with 45–53% silica, is low-viscosity and flows rapidly over long distances, while andesitic or rhyolitic lava, with higher silica (up to 70%), is more viscous and tends to form thick, steep-sided domes or short flows. Temperatures range from about 700°C for rhyolitic lava to over 1,200°C for basaltic varieties, allowing basaltic flows to travel tens of kilometers at speeds up to 10 km/h on steep slopes, whereas highly viscous flows advance at mere meters per hour. Common minerals in these lavas include olivine, pyroxene, and plagioclase, particularly in basaltic types erupted at 1,100–1,250°C. Lava flows exhibit distinct surface textures that reflect their flow dynamics, with pāhoehoe featuring smooth, ropy, or billowy surfaces formed by slow, insulated movement in lobes or tubes, and 'a'ā displaying rough, jagged, clinkery exteriors from faster, fracturing advances in open channels. These textures arise from differences in gas content, crystal formation, and effusion rates; for instance, pāhoehoe retains more spherical gas bubbles and fewer crystals due to sustained heat, while 'a'ā develops irregular bubbles and more crystals from cooling. Although lava flows rarely cause direct fatalities due to their typically slow speeds (often less than 1 km/h on gentle slopes), they can trigger secondary dangers like wildfires, gas emissions, or lahars from interactions with water or ice.

Introduction

Definition

Lava is defined as molten or partially molten rock that is expelled onto Earth's surface during a volcanic eruption, where it flows or spreads before cooling and solidifying to form extrusive igneous rock. This material originates from deeper within the planet and emerges through volcanic vents, fissures, or other openings, maintaining its integrity as a fluid or viscous mass upon eruption. A key distinction exists between lava and magma: magma refers to molten or partially molten rock beneath Earth's surface, while lava describes the same material only after it reaches the surface and is no longer confined by lithostatic . This transition occurs as magma ascends and erupts, with the sudden decrease in pressure causing dissolved volatiles—such as , , and —to exsolve rapidly through , often leading to or effusive behavior. Lava can exist in various states, primarily as fully molten liquid but also as partially molten mixtures containing suspended crystals, which influence its and flow characteristics. Lava primarily occurs during volcanic eruptions, issuing from central vents in stratovolcanoes, fissures in shield volcanoes, or collapse structures like calderas, where it contributes to the formation of diverse landforms upon cooling. While overwhelmingly associated with volcanic activity, rare non-volcanic contexts include molten rock generated by impacts, which can produce impact melt sheets resembling lava flows, and industrial analogs such as molten in that mimic lava's .

Etymology

The term "lava" derives from the Italian word lava, signifying "a stream" or "flood," which locals near applied to molten rock flows in the early , evoking the material's rapid, washing descent down slopes. This usage stemmed from the Latin lavare ("to wash") or possibly labes ("a fall" or "slide"), roots that underscore the fluid, cascading behavior observed during eruptions. The word first appeared in English around 1750 to describe volcanic molten rock, marking its transition from regional dialect to scientific lexicon. English adoption accelerated through eyewitness accounts of Vesuvius activity, particularly Sir William Hamilton's detailed observations in his 1776–1779 work Campi Phlegraei, where he employed "lava" to depict fiery streams pouring from the volcano, drawing on Neapolitan terminology encountered during his residency in from the 1760s. By the , the term permeated geological texts, such as those by , solidifying its role in describing extrusive igneous processes and distinguishing it from subsurface . This evolution resolved earlier ambiguities in ancient descriptions, like Pliny the Younger's 79 AD letters portraying Vesuvius's outburst as towering flames and "gushing" fires that darkened the sky, which lacked a precise term for flowing molten material. Related terminology enriched via indigenous languages, notably Hawaiian words for flow morphologies: pāhoehoe (smooth, ropy lava, from hoe meaning "to paddle," evoking swirled patterns) and ʻaʻā (rough, clinkery lava, implying "stony" or "to burn"). These were formalized in by Clarence E. Dutton in 1884, integrating cultural observations from into global nomenclature and highlighting lava's diverse surface expressions.

Properties

Composition

Lava is predominantly composed of , which constitute over 90% of terrestrial lavas, primarily in the form of oxides such as (SiO₂) ranging from 45% to 75%, along with aluminum oxide (Al₂O₃), (FeO), (MgO), (CaO), (Na₂O), and (K₂O), in addition to volatiles like (H₂O), (CO₂), and (SO₂). Silicate lavas are classified based on their silica content and into , intermediate, and types. Basaltic lavas, which are and rich in iron and magnesium, contain 45-52% SiO₂ and feature minerals such as , , and . Andesitic lavas, intermediate in composition, have 52-63% SiO₂ and include , , and as key minerals. Rhyolitic lavas, which are and enriched in silica and aluminum, exceed 63% SiO₂ (often 69-80%) and consist mainly of , alkali feldspar, and . Representative examples include the low-silica basalts of Hawaiian volcanoes, such as those from , and the high-silica rhyolites of Yellowstone. Non-silicate lavas are rare and include carbonatites, which are carbonate-rich with less than 3% silica and dominated by sodium- and potassium-bearing carbonates like nyerereite and gregoryite, as seen in eruptions at Oldoinyo Lengai in Tanzania. Sulfur lavas, composed primarily of molten elemental sulfur, occur sporadically, such as at Lastarria volcano in northern Chile, where flows form due to melting of sulfur deposits in fumarolic areas. These non-silicate types exhibit low viscosity attributable to their compositions. The silica content in lavas fundamentally influences their and resultant eruption styles, with higher silica leading to increased and resistance to flow. Isotopic ratios, such as those of (Sr), (Nd), lead (Pb), and oxygen (O), help trace lava origins, distinguishing mantle-derived signatures (e.g., relatively primitive ratios) from those contaminated by crustal material. This compositional aspect affects rheological properties, such as flow behavior.

Rheology

Rheology encompasses the study of deformation and flow in materials under applied stress. For lava, this involves analyzing how molten rock responds to shear forces during emplacement, often displaying non-Newtonian rather than simple viscous flow. Lavas commonly exhibit shear-thinning properties, where decreases with increasing , or behave as Bingham plastics, requiring a minimum yield stress before flow initiates. Lava viscosity spans a wide range, typically from 10 to 10610^6 Pa·s, governed primarily by , silica content, fraction, and gas bubble content. The dependence can be approximated by the : η=Aexp⁡(BT)\eta = A \exp\left(\frac{B}{T}\right) where η\eta is the , TT is the in , and AA and BB are empirical constants specific to the lava composition. Higher silica content elevates by strengthening the network, leading rhyolitic lavas to resist flow far more than low-silica basaltic varieties. Increasing fraction and gas bubbles also raise effective , as crystals impede molecular motion and bubbles disrupt the melt , though bubbles can sometimes enhance shear-thinning under flow. inversely affects , with even modest cooling—such as a 10°C drop—roughly doubling it in basaltic systems due to the exponential relationship. further increases by causing bubble collapse and reducing melt , transitioning the material toward a denser, more rigid state. As lava flows advance and cool, a crystallization front propagates inward from the surface, progressively solidifying the outer layer into a rigid crust while the interior remains molten. This process imparts yield strength to the flow, particularly in blocky varieties, where the crust's resistance to shear prevents further deformation and shapes the final morphology. The yield strength arises from the interplay of cooling-induced and crust formation, ultimately halting flow when stresses fall below the material's threshold.

Temperature

Lava erupts at temperatures generally ranging from 650°C to 1250°C, with variations primarily determined by its . Basaltic lava, the most common type, typically erupts at 1000–1200°C, while andesitic lava erupts at 900–1100°C, and rhyolitic lava at 700–900°C. In rare instances, superheated basaltic lava can reach up to 1400°C due to deeper mantle origins before cooling during ascent. Measuring lava temperatures involves several techniques, each suited to different conditions and distances. Direct methods include probes inserted into active flows, providing precise interior readings up to 1200°C or more. Optical pyrometry estimates temperature based on the visible glow color: dull red indicates around 600°C, bright orange-yellow about 1000–1100°C, and incandescent white exceeds 1200°C. This glow is produced by incandescence, the emission of visible light through blackbody radiation at high temperatures, with the observed colors closely matching blackbody radiation expectations for the temperature range. The intense brightness and vivid coloration can create the subjective impression that lava is "thousands of degrees" hot, but measured temperatures for basaltic lava are typically 1000–1200°C, consistent with these optical observations. For , satellite-based instruments like NASA's MODIS detect radiance from lava surfaces, enabling global monitoring of eruption hotspots with resolutions down to 1 km. Once erupted, lava cools rapidly at the surface, forming a solid crust typically when the temperature drops to –1000°C, while the interior remains molten. Cooling rates depend on flow thickness, emplacement environment, and atmospheric conditions; thin flows in air may solidify in days, but thicker ones (e.g., 4.5 m) require over 130 days to cool to about 200°C (290°F). Subaqueous flows cool much faster due to water's high , often forming pillow structures within hours. Heat loss from lava flows occurs primarily through radiation, convection, and conduction. Radiative heat transfer follows the Stefan-Boltzmann law, expressed as
Q=ϵσT4Q = \epsilon \sigma T^4
where QQ is the (W/m²), ϵ\epsilon is the (approximately 0.9 for molten lava), σ=5.67×10−8\sigma = 5.67 \times 10^{-8} W/m²K⁴ is the Stefan-Boltzmann constant, and TT is the absolute temperature in ; this mechanism dominates at high temperatures above 1000°C. Convection transfers heat to the surrounding air or via motion, while conduction occurs through the developing crust to the substrate, slowing overall cooling as insulation builds. These processes influence , with declining temperatures increasing resistance to flow.

Flow Types

ʻAʻā

ʻAʻā lava flows are characterized by a rough, jagged surface composed of broken blocks known as clinkers, typically 1-2 meters in size, which create a spiny, rubbly texture that is highly frictional and difficult to traverse. These flows generally have a total thickness of 3-15 meters and advance slowly, at rates of a few meters per hour, though surges can occur up to 100 meters in minutes. In contrast to smoother pāhoehoe flows, the clinkery surface of ʻaʻā results from the continual disruption of its cooling crust. The formation of ʻaʻā occurs primarily in basaltic to andesitic lavas of relatively high effective , where internal shear stresses cause the outer crust to break repeatedly as the flow advances. This self-breaking process, often termed autobrecciation, generates rubble from the fragmented crust, with new clinkers forming as underlying molten lava pushes forward and tears the solidified material. and gas loss further thicken and granulate the lava, promoting the development of the characteristic spinose morphology in open channels during high-effusion-rate eruptions. ʻAʻā flows are common in longer eruptions, particularly those extending over 10 kilometers, such as the 1984 Mauna Loa eruption on Hawaiʻi, where channelized ʻaʻā flows advanced up to 26 kilometers from the vents. They often form through transitions from pāhoehoe when flows encounter steeper slopes, increased shear, or prolonged cooling that stiffens the crust. This fragmentation dissipates through constant crustal rupture, resulting in higher overall flow resistance and slower propagation compared to less disrupted flow types.

Pāhoehoe

Pāhoehoe lava flows exhibit a distinctive smooth, billowy, and undulating surface characterized by rope-like folds, resulting from the folding of a thin, crust as the underlying molten lava continues to move. The term "pāhoehoe" originates from the , meaning "smooth" or "unbroken lava," reflecting its polished, ropy texture that contrasts with the rough, clinkery surface of ʻaʻā flows. These flows typically advance at rates of 1–50 meters per hour due to their low friction and fluidity, forming thin sheets ranging from 0.1 to 1 meter in thickness. Pāhoehoe forms primarily in low-viscosity basaltic lavas through ductile flow mechanisms, where the molten material deforms plastically without fracturing, often leading to as lava accumulates beneath a cooling crust. Common subtypes include shelly pāhoehoe, which develops inflated lobes from pressurized buildup under the crust, and slabby pāhoehoe, featuring partially broken and upturned slabs of crust that remain cohesive overall. This formation process is facilitated by conditions, where helps maintain the intact crust, and retention of dissolved gases prevents excessive that could disrupt the smooth morphology. Pāhoehoe is predominant on shield volcanoes, such as in Hawaiʻi, where low slopes and sustained eruption rates favor its development. For instance, during the 2018 lower East eruption of , pāhoehoe flows from fissure 8 covered approximately 35.5 square kilometers of land. These flows can transition to ʻaʻā morphology downstream if conditions change, such as steeper slopes accelerating shear or prolonged cooling increasing .

Block Lava

Block lava flows are characterized by a surface of angular, coherent blocks, typically ranging from 1 to 5 meters across, that form as the rigid crust fractures and rides atop a highly viscous, paste-like interior. These flows exhibit very slow advance rates, often on the order of millimeters per hour to meters per day, resulting in steep, near-vertical fronts due to limited spreading. They are predominantly associated with silicic compositions, such as rhyolitic and dacitic lavas, where silica contents exceed 63 weight percent, leading to high viscosity that inhibits fluid motion. The formation of block lava occurs in settings with high yield strength, where the lavas' near-solid consistency prevents significant internal deformation or flow; instead, blocks originate from the rapid and fracturing of the flow margins, which then tumble and override the advancing front. This process is exacerbated by the rheological behavior akin to a , promoting a regime in which the outer crust moves as a cohesive unit with minimal shearing in the core. Block lava flows commonly occur during eruptions of silicic volcanoes, such as the 1915 dacitic eruption at , , where incandescent blocks cascaded down the flanks, or the 1980-1986 dome-building phase at , Washington, involving extrusion of viscous . Due to their sluggish mobility, these flows rarely extend beyond 1 kilometer in length, often piling up into stubby, thick accumulations near the vent.

Pillow Lava

Pillow lavas form distinctive rounded, sack-like structures typically 0.3 to 1 meter in diameter, characterized by a smooth, glassy outer rind that develops upon rapid cooling and often features radial contraction cracks extending inward from the surface. These pillows accumulate in stacked mounds or sheet-like deposits, creating thick sequences of bulbous or elongate masses that can reach tens of meters in height, with the glassy rinds preserving evidence of the original fluid extrusion. The internal texture transitions from the fine-grained or glassy margin to coarser crystallization toward the core, reflecting progressive cooling rates. The formation of pillow lavas occurs exclusively in subaqueous environments, where molten erupts or flows into , leading to instantaneous that forms a brittle crust around the still-fluid interior. This rapid cooling, often from temperatures exceeding 1000°C in contact with ambient near 0-4°C, causes thermal contraction that generates quench textures, including pervasive radial fractures as the contracting material pulls away from the rigid rind. As pressure builds within the inflating , the crust ruptures, allowing new lobes of lava to extrude and form interconnected clusters; associated breccias arise from non-explosive fragmentation of the chilled margins or minor steam explosions that shatter the outer glass into angular shards. Pillow lavas are prevalent at mid-ocean ridges, seamounts, and during eruptions into lakes or shallow seas, where they build up as primary volcanic constructs indicating submerged paleoenvironments at various water depths. A notable example is the submarine flows from Kilauea Volcano's 1953 eruption, which produced extensive pillow complexes as lava entered coastal waters, demonstrating how such features record episodic underwater volcanism. Their widespread occurrence throughout Earth's geologic record, from Archean greenstone belts to modern oceanic crust, underscores their role as the dominant form of subaqueous basaltic volcanism.

Landforms

Cinder and Spatter Cones

Cinder and spatter cones are small volcanic landforms constructed primarily from fragmented lava ejected during mild explosive eruptions, such as Strombolian activity, where gas expansion propels molten blobs into the air to solidify as they fall back around the vent. These blobs, known as cinders or spatter, accumulate to form steep-sided cones with heights typically ranging from 10 to 400 meters and slopes often exceeding 30 degrees, reflecting the angle of repose for loose pyroclastic material. The process begins with the ejection of viscous lava fragments from a central vent, which follow ballistic trajectories determined by their launch velocity and angle, ultimately shaping the cone's symmetrical profile. Cinder cones consist of loose, oxidized and deposits that impart a reddish hue due to interaction with atmospheric oxygen, while spatter cones form from hotter, more cohesive fragments that partially weld upon landing, resulting in darker, agglutinated structures. Spatter cones are generally smaller, often less than 10 meters high, and built of agglutinate with a more consolidated texture compared to the friable cinder varieties. Both types typically derive from basaltic to andesitic magmas, which provide the moderate and gas content necessary for such fragmented eruptions. These cones commonly occur in monogenetic volcanic fields, where eruptions are short-lived and localized to a single vent, as exemplified by in , which emerged in a cornfield in 1943 and grew to 424 meters high by the end of its nine-year activity in 1952. rapidly affects these structures due to their unconsolidated nature, often exposing internal layering of alternating cinder and spatter deposits that record the eruption's progression. A key aspect of their formation involves the retention of heat in ejected fragments, enabling when temperatures exceed 900°C upon impact, which fuses clasts into more stable aggregates while cooler cinders remain discrete. This thermal threshold, combined with ballistic fallout patterns, limits cone growth and distinguishes these features from other lava-built landforms.

Kīpukas

A kīpuka is an area of elevated older terrain, such as hills or forested patches, completely surrounded by younger lava flows, forming vegetated "islands" amid a of recent volcanic deposits. The term derives from the Hawaiian word kīpuka, meaning an "opening" or variation in form, and has been adopted into geological terminology to describe these features. Kīpukas form when advancing lava flows encounter and divert around topographic highs, such as ridges or pre-existing landforms, leaving the enclosed areas untouched and preserving their original , , and . This process can occur with both ʻaʻā and pāhoehoe flows that split and reunite downslope. These isolated remnants vary widely in size, from small patches of a few square meters to larger areas spanning several square kilometers. Kīpukas exhibit distinct characteristics shaped by their isolation, including mature ecosystems that contrast sharply with the surrounding barren lava. Their edges often face heightened exposure to wind and , contributing to localized that can gradually reshape boundaries over time. Ecologically, they support unique as refuges for , where isolation limits invasion by non-native plants and animals, fostering conditions for endemic taxa to persist or even speciate. On , for instance, kīpukas harbor endemic birds like the ʻapapane (Himatione sanguinea) and diverse native flora adapted to volcanic soils. Kīpukas are common on the flanks of Hawaiian shield volcanoes like Kīlauea, where frequent eruptions create patchwork landscapes. The long-lived Puʻu ʻŌʻō eruption (1983–2018) at Kīlauea produced numerous kīpukas by encircling older forested areas near the East Rift Zone, preserving habitats amid extensive new flows. These features are vital for scientific study, acting as natural laboratories for observing primary , where propagules from kīpukas rapidly colonize adjacent sterile lava, rebuilding native forests in decades.

Lava Domes and Coulées

Lava domes and coulees are landforms created by the of highly viscous, silica-rich lava, typically rhyolitic or dacitic in composition, which resists flowing and instead accumulates near the volcanic vent. Lava domes form as steep-sided, bulbous plugs or mounds, often 10 to 1,000 meters high, with craggy surfaces resulting from the cooling and fracturing of the outer layers as new material pushes upward. In contrast, coulees develop as thicker, tongue-shaped flows that extend farther, sometimes up to 5 kilometers or more, while maintaining a steep profile due to the lava's high yield strength and limited mobility. These structures commonly appear within craters or on the flanks of stratovolcanoes, where the viscous piles up rather than spreading widely. The formation of lava domes and coulees involves the effusive eruption of gas-poor, viscous that builds structures through two primary growth mechanisms: endogenous and exogenous expansion. Endogenous growth occurs when incoming lava intrudes into the dome's interior, causing pressure buildup that compresses and uplifts existing layers, often resulting in faulting and radial cracking on the surface. Exogenous growth, on the other hand, happens through the overflow of new lava lobes at the surface, forming asymmetric additions or spines that extend outward from the vent. This dual process allows domes to evolve over weeks to years, with the transition between endogenous and exogenous phases influenced by supply rates and internal pressures. Due to their steep slopes and brittle outer shells, lava domes and coulees are prone to instability, where gravitational collapse of oversteepened margins can generate pyroclastic flows or rockfalls. Such collapses often occur as the dome grows, releasing hot debris that travels downslope at high speeds. Notable examples include the Novarupta lava dome in Alaska, formed during the 1912 eruption as a rhyolitic plug approximately 70 meters high and 380 meters wide, which plugged the vent following explosive activity. Similarly, the 2008 eruption of Chaitén volcano in Chile produced multiple rhyolite domes within the caldera, reaching up to 120 meters in height through rapid endogenous and exogenous growth phases after an initial explosive stage.

Lava Tubes

Lava tubes form primarily in low-viscosity pāhoehoe flows, where the outer layer of molten lava cools and solidifies into a crust over an active channel, creating a subsurface conduit insulated from the atmosphere. This crust develops centrally in the channel due to radiative and convective cooling, with dropping below the yield strength of the solidifying lava (typically around 8100 Pa asymptotically), allowing the roof to stabilize and extend downslope. The process is favored on gentle slopes (≤6°) and in wider channels (>23.6 m), where low effusion rates (<10 m³/s) promote crust formation without excessive disruption. Thermal by the roof minimizes heat loss, enabling sustained flow over distances of several kilometers, while of the hotter, less dense interior lava supports the cooler crust overhead, driving segregation of the flow into a tubular structure. Characteristics of lava tubes include sinuous, tunnel-like voids with diameters ranging from 1 to 20 m, formed after the molten core drains away, leaving behind a hollow space often lined with breakdown rubble from collapses. Internal features commonly include lava stalactites—dripping formations from the ceiling—remnant levees along the walls, and secondary mineral deposits from post-flow cooling and interaction. Skylights, or collapse pits in the , provide access points and indicate structural weaknesses, while the tubes' smooth, sculpted walls reflect the of the original flow, with depths typically 5–6 feet for active streams moving at speeds under 2 mph. These conduits enhance flow efficiency by protecting lava from cooling, but partial s can widen the system or redirect flows. Lava tubes occur worldwide in basaltic volcanic regions, with notable examples in , where they facilitate long-distance transport during eruptions. The Thurston Lava Tube (Nāhuku) in is an approximately 180 m (600 ft) long, 500-year-old example formed by a river of lava at approximately 2000°F, now accessible via a rainforest trail and featuring microbial colonies on its walls. The longest known system, on Volcano, extends 65.5 km with a maximum depth of 1,102 m and an average slope of 1.9°, illustrating how tubes can propagate extensively from high-elevation vents downslope. On other planets, such as Mars, lava tubes identified on Alba Mons suggest similar formation processes and potential astrobiological habitats due to their stable, shielded environments.

Lava Lakes

Lava lakes are persistent bodies of molten confined within volcanic craters or vents, exhibiting dynamic surfaces characterized by , gas emissions, and periodic crust formation. These lakes typically range in size from tens of meters to about 1 kilometer in , with convecting surfaces driven by differences that cause cooler, solidified crust to sink and be replaced by hotter liquid , leading to overturn and renewal of the surface. Gas plumes, rich in , , , and , rise continuously from the lake, often forming visible steam clouds that can extend for kilometers downwind. For instance, the in Hawaii's volcano displays these features, with a surface area reaching up to 300 acres during active periods and recurring crustal foundering that maintains its molten state. As of 2025, episodic fountaining in since December 2024 has continued, with reforming during active phases. Lava lakes form through the ponding of magma supplied continuously from underlying reservoirs, allowing molten material to accumulate in a stable depression while undergoing degassing that releases volatile components and sustains the lake's activity. This sustained supply, often at rates of 0.6–3.5 cubic meters per second, prevents complete solidification and promotes buoyancy-driven circulation. Active lava lakes, such as that in Nyiragongo volcano in the Democratic Republic of Congo, maintain vigorous convection and open degassing, with the lake filling an inverted cone-shaped conduit connected to deeper magmatic sources at 1–4 km and 10–14 km depths. In contrast, inactive lava lakes may develop thick crusts or solidify entirely when magma supply diminishes, transitioning into crater lakes filled with water or cooled rock, though these no longer exhibit molten behavior. Notable occurrences include the long-persisting lava lake in , , which has remained active since at least 1972 within a 250-meter-wide inner , providing a rare example of continuous phonolitic convection in an . Monitoring of such lakes often involves seismic observations to detect convection cells, where low-frequency tremors signal subsurface circulation and surface disruptions like spattering or overturn. At , seismicity has revealed persistent cycles of lake motion lasting 5–18 minutes, linked to these convective processes. Surface temperatures in active lava lakes typically exceed 1000°C, reflecting intense . A fundamental aspect of lava lake stability is the heat balance, where magmatic heat input from below—via and fresh influx—equates to losses through surface radiation, convective gas transfer, and conduction, preventing either overheating or freezing. In early-stage lakes, this balance can manifest as fountaining along the edges, where buoyant gas-rich foam rises and erupts, as observed in foam-dominated systems like those at Nyiragongo. Mature melt-dominated lakes, such as , achieve equilibrium with higher radiative power output, up to 5 × 10^8 watts, balanced by reduced gas emissions. This dynamic equilibrium underscores the lakes' role as natural laboratories for studying open-vent .

Lava Deltas

Lava deltas form when pāhoehoe-type basaltic lava flows advance into bodies of , such as oceans or lakes, typically through insulated tube systems that allow the molten material to extend seaward without immediate cooling. Upon entering the water, the denser lava undergoes underflow due to the density contrast between the molten rock and the surrounding fluid, driving it beneath the water surface to build submerged foundations. This process is accompanied by quench fragmentation, where rapid cooling of the hot lava in contact with cold causes thermal stresses that shatter the material into angular fragments, forming the structural base of the delta. As the lava continues to advance, the emergent front periodically collapses, creating unstable benches that extend the platform but remain prone to slumps involving drops of 10-50 meters. These features manifest as layered, shelf-like platforms that prograde body, typically ranging from 10 to 300 in width and composed of stacked sequences of fragmented , intact lava flows, and rubble. The margins often feature pillow-shaped lobes formed by subaqueous , surrounded by accumulations of coarse breccias and talus derived from failures and collapses. The layered results from repeated episodes of density-driven flows and chutes that deposit material in foreset beds, creating a prograding similar to sedimentary deltas. While the outer edges may include pillow lavas indicative of , the overall platform remains subaerially capped during active growth. Lava deltas are common at basaltic volcanic islands, particularly in , where they have extended coastlines by hundreds of meters during prolonged eruptions. Similar growth occurred at the Kamoamoa site during the 1992-1994 activity, where the delta reached 500 meters wide and 2.9 kilometers long, adding significant new land area. The East Lae ‘Apuki delta from the 2005-2007 episode extended the shoreline through ongoing progradation but exhibited rates of several centimeters per month due to . These structures pose hazards from sudden foundering and collapses, which can generate explosions, tsunamis, and boulder fields hundreds of meters inland, as observed in multiple events.

Eruptive Features

Volcanoes

Lava serves as the primary material in constructing major volcanic edifices through the accumulation of flows and domes, forming the foundational layers that define a volcano's structure and longevity. In shield volcanoes, low-viscosity basaltic lava floods spread widely, building broad, gently sloping cones over time; in exemplifies this, rising more than 4 km above sea level through repeated effusive eruptions. These structures grow primarily from fluid flows that travel great distances, creating a shield-like profile rather than steep peaks. Stratovolcanoes, also known as composite volcanoes, develop through alternating layers of lava flows and deposits from both effusive and explosive activity, resulting in steep-sided, symmetrical cones. in illustrates this composite build, where viscous andesitic to dacitic lavas interbed with pyroclastic materials to form a classic conical shape exceeding 3,700 m in height. Calderas represent a dramatic phase in volcanic evolution, forming when large volumes of drain from shallow chambers during major eruptions, causing the overlying edifice to collapse into a basin-shaped depression often kilometers wide. This process, observed in historical events like the 2018 eruption, highlights how lava withdrawal destabilizes the structure above. Volcanic edifices evolve through distinct growth phases, including initial shield building followed by potential flank eruptions that extend the volcano's footprint and redistribute stress. Flank vents, common in shields like , allow lava to erupt away from the summit, contributing to lateral expansion over thousands of years. An extreme example is on Mars, the solar system's largest volcano at 22 km high, formed by immense piles of basaltic lava flows over billions of years due to prolonged effusive activity in a tectonically stable environment. The balance between effusive lava output and explosive events fundamentally shapes these edifices, with dominant effusive regimes producing broad and mixed activity yielding steeper stratovolcanoes. Volume estimates for such structures are derived from mapping individual flow units, combining areal extent with thickness measurements to quantify total erupted material, as applied to Hawaiian shields revealing billions of cubic meters accumulated.

Lava Fountains

Lava fountains are high-velocity jets of molten basaltic lava ejected from volcanic vents during effusive eruptions, driven by the rapid release of dissolved gases within the . These phenomena typically occur in low-viscosity basaltic magmas, where gas exsolution propels the lava upward in a continuous or pulsating stream, distinguishing them from more explosive styles like Strombolian eruptions. The characteristics of lava fountains include heights ranging from 10 to 500 meters, though exceptional cases exceed this, with durations sustained from 10 minutes to several hours. They are predominantly gas-driven, with the exsolved volatiles providing the necessary thrust for ejection, and the resulting spatter—partially cooled lava fragments—often accumulates to form small spatter cones around the vent. Fountains are most common in basaltic settings due to the magma's low silica content and high fluidity, allowing efficient gas escape without fragmentation into fine . Formation of lava fountains begins with pressure release at the vent as ascends, where decreasing confinement causes dissolved gases to exsolve rapidly and accelerate the . This process can be approximated by the ballistic for fountain h≈v22gh \approx \frac{v^2}{2g}, where vv is the exit velocity of approximately 50–200 m/s and gg is (9.8 m/s²); velocities in this range correspond to observed heights through simple under negligible air resistance. Bubble expansion within the provides the primary thrust, as gas pockets coalesce into layers that fragment near the surface, propelling the mixture outward. Lava fountains frequently serve as precursors to extensive lava flows, transitioning from vertical ejection to lateral spreading as gas content diminishes. A notable occurrence was during the 1969 Mauna Ulu eruption at Volcano, , where fountains reached a maximum height of 540 meters over multiple episodes, feeding subsequent flows that covered over 10 km². A key concept in lava fountain dynamics is the role of bubble expansion in generating thrust, which drives the initial jet, while rapid cooling of molten droplets in mid-air produces solid clasts that contribute to fallout and spatter deposits. This aerial cooling limits the cohesion of ejected material, resulting in a characteristic spray of fragments rather than a unified stream.

Hazards and Impacts

Direct Effects of Lava Flows

Lava flows pose immediate physical dangers primarily through three mechanisms: burial, thermal incineration, and toxic gas emissions. Advancing flows bury structures, vegetation, and landscapes under layers of solidified rock, with thicknesses typically ranging from a few meters to tens of meters, though accumulations can reach up to 100 feet (30 meters) in some cases, completely entombing anything in their path. The extreme heat of molten lava, exceeding 1000°C (1800°F) and reaching up to 1200°C (2200°F) in basaltic flows, causes rapid incineration of organic materials and melting of infrastructure such as metals and asphalt, which begins to deform at temperatures around 700°C. Additionally, volcanic gases released from lava flows, including carbon dioxide (CO₂) and sulfur dioxide (SO₂), can accumulate in low-lying areas or be carried by winds, leading to asphyxiation risks for humans and animals due to oxygen displacement or respiratory irritation. The speed and extent of lava flows determine their reach and destructive potential, allowing them to travel distances of 1 to 50 kilometers depending on slope, lava viscosity, and eruption volume. On steep slopes, flows can advance at rates up to 48 kilometers per hour (30 ), though most progress at less than 1 kilometer per hour (0.6 ) on gentler , providing variable time for evacuation but igniting wildfires and melting utilities like power lines and roads along the way. Behavior variations among flow types, such as 'a'ā (rough, fast-moving) versus pāhoehoe (smooth, slower), influence these dynamics but do not alter the core destructive processes. Efforts to mitigate direct lava flow effects focus on slowing or redirecting advances, though success is limited by the scale and unpredictability of eruptions. Earthen barriers, constructed from or previous flows, can temporarily deflect or smaller flows on sloped ground, but they often fail against large volumes, as seen in experimental setups where barriers widen flows rather than stop them. , involving spraying seawater on the flow front to accelerate solidification, has been attempted in and elsewhere, potentially reducing advance rates by up to 50% by forming a crust that impedes further movement, yet it risks explosions and generation from dissolved gases, limiting its effectiveness to specific scenarios. Overall, these interventions provide only short-term protection, emphasizing the primacy of evacuation and zoning in hazard management.

Historical Examples of Destruction

One of the most notable historical instances of lava flows destroying a settlement occurred during the 1983–2018 Puʻu ʻŌʻō eruption of Kīlauea volcano in Hawaii, which reached its peak destructiveness in 1990 when tube-fed pāhoehoe and ʻaʻā flows advanced into the Kalapana community on the island's southeast shore. Beginning in March 1990, breakouts from an underground lava tube system progressively overran the area, destroying approximately 180 homes, including the historic 19th-century Kalapana village, and burying over 8 kilometers (5 miles) of state highway under up to 35 meters (115 feet) of solidified lava. The slow advance of the flows, typically at rates of 1–10 meters per hour, allowed for evacuations over several days, with residents given warnings as the front approached individual properties; however, the relentless progression ultimately displaced hundreds and covered 200 hectares (500 acres) of land, reshaping the coastline with new lava deltas. Post-event, the community was not rebuilt in the original location due to ongoing volcanic risk, but cultural sites were preserved, highlighting patterns of permanent relocation in response to recurrent Hawaiian shield volcano activity. A more recent example unfolded during Kīlauea's 2018 lower East Rift Zone eruption, which began on May 3 and primarily affected the Leilani Estates subdivision in the Puna district of Hawaii's Big Island. Fissure 8 within the subdivision produced vigorous spatter and fountaining, feeding fast-moving ʻaʻā flows that partially engulfed Leilani Estates and nearby areas, destroying over 700 structures across 14 square miles (36 square kilometers) of land, though the core subdivision saw about 100 homes lost. Evacuations commenced immediately upon the first fissures opening, with timelines extending days to weeks as flows advanced at speeds up to 800 meters per hour in channels but slowed near inhabited zones, enabling phased retreats and pet rescues; emissions and ground cracks further complicated responses, displacing over 2,000 residents. Unlike full obliteration, partial damage in Leilani Estates allowed for selective rebuilding after the eruption ended in August, with hardened lava flows now integrated into community planning, underscoring adaptive strategies for fissure-fed eruptions. The 2021 eruption of on in Spain's , lasting from September 19 to December 13, provides a more recent example of extensive lava flow destruction in a populated area. The eruption produced over 200 million cubic meters of basaltic to trachytic lava, covering about 1,200 hectares and destroying more than 1,300 buildings, including approximately 1,000 homes, primarily in the towns of Todoque, La Laguna, and surrounding neighborhoods. Flows advanced at rates up to several hundred meters per day, burying agricultural lands (especially banana plantations), roads, and water systems, while entering the and creating new land; over 7,000 were evacuated, with no fatalities, but economic losses exceeded €900 million. Mitigation attempts, including monitoring and evacuation, were effective, but rebuilding remains ongoing as of 2025, with challenges from ash fallout and gas emissions. This event highlighted vulnerabilities in insular volcanic settings and the role of early warning systems. In 1973, the eruption of volcano on Island, part of Iceland's archipelago, demonstrated successful human intervention against encroaching lava flows, saving much of the town of from total destruction. The eruption began on January 23, producing basaltic fissure flows that rapidly advanced toward the harbor and residential areas, destroying about 400 buildings and burying one-third of the island under up to 20 meters (65 feet) of and lava, but the main flows were halted through innovative cooling efforts. Icelandic authorities, supported by international aid, deployed over 40 pumps to spray onto the advancing front at rates exceeding 1,000 liters per second, forming a barrier of solidified crust that diverted the flow and preserved the vital fishing harbor; aerial bombing was considered to disrupt the flow but deemed unnecessary as cooling proved effective. With the eruption's sudden onset, the entire population of 5,300 was evacuated by boat and air within hours, contrasting the slower Hawaiian timelines, yet post-eruption rebuilding proceeded swiftly, with the town repopulated by 1974 and the added land enhancing the harbor's capacity. This event established a precedent for proactive in populated volcanic zones, emphasizing rapid response and to manage basaltic flow threats.

Environmental Consequences

Lava flows initially sterilize landscapes by incinerating and burying soil, creating barren surfaces that undergo primary . , such as lichens (e.g., Stereocaulon vulcani), colonize these surfaces within 1-2 years, initiating and that facilitate subsequent plant establishment. In humid environments like , vascular plants and shrubs appear within decades, leading to development in 100-150 years, with moisture playing a key role in accelerating this process. Kipukas—isolated patches of pre-existing surrounded by fresh lava—serve as hotspots, acting as refugia for and sources for recolonization, enhancing regional ecological recovery. Large effusive eruptions can induce significant climatic perturbations through gas emissions. The 1783-1784 fissure eruption in extruded approximately 15 km³ of and released 122 megatons of SO₂, forming aerosols that caused cooling of about 1.3°C for several years, exacerbating winter severity and contributing to crop failures. These aerosols reduced solar radiation, illustrating how flood eruptions can temporarily alter global temperatures. Geologically, lava emplacement drives long-term through . Basaltic lavas, rich in ferromagnesian minerals, weather relatively quickly in humid climates to form fertile Andisols, which develop characteristic amorphous clays and high nutrient retention within 1,000-5,000 years, supporting productive ecosystems. Additionally, weathering facilitates natural by mineralizing atmospheric CO₂ into stable carbonates, contributing 30-35% of global terrestrial CO₂ drawdown over geological timescales. Recent studies highlight ongoing environmental impacts from eruptions. The 2021 Cumbre Vieja eruption on emitted approximately 19 Mt of CO₂, equivalent to about 10% of Spain's annual anthropogenic emissions, underscoring the climatic forcing potential of even moderate events. Submarine lava flows exacerbate by releasing dissolved CO₂, as observed during the 2011 eruption, where dropped by up to 2.8 units locally, altering marine carbonate chemistry and stressing calcifying organisms. A key aspect of lava's environmental legacy is nutrient enrichment from rapid breakdown, releasing bioavailable elements like , , and magnesium that boost post-eruption primary productivity and accelerate . This process transforms initially inhospitable terrain into highly fertile ground, as seen in volcanic soils supporting diverse .

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