A former island is a mass of land that was once an island, but has been joined to a mainland, another island, or engulfed by a body of water. The process of joining might be the result of volcanic activity, moving tidal sands, or through land reclamation. Islands engulfed by the sea may have lowered because of subsidence, tectonic activity, erosion, or rising sea levels. For example, the New Moor island in Bangladesh existed in the 1970s, but was engulfed by the Bay of Bengal in 2011.