In geomorphology, an outburst flood—a type of megaflood—is a high-magnitude, low-frequency catastrophic flood involving the sudden release of a large quantity of water. During the last deglaciation, numerous glacial lake outburst floods were caused by the collapse of either ice sheets or glaciers that formed the dams of proglacial lakes. Examples of older outburst floods are known from the geological past of the Earth and inferred from geomorphological evidence on Mars. Landslides, lahars, and volcanic dams can also block rivers and create lakes, which trigger such floods when the rock or earthen barrier collapses or is eroded. Lakes also form behind glacial moraines or ice dams, which can collapse and create outburst floods. Definition and classification Megafloods are paleofloods (past floods) that involved rates of water flow larger than those in the historical record. They are studied through the sedimentary deposits and the erosional and constructional landforms that individual megafloods have created. Floods that are known to us through historical descriptions are mostly related to meteorological events, such as heavy rains, rapid melting of snowpacks, or combination of these. In the geological past of the Earth, however, geological research has shown that much larger events have occurred. In the case of outburst floods, such floods are typically linked to the collapse of a barrier which formed a lake. They fall in the following classification according to the mechanism responsible: Collapse of glacier dams that impound proglacial lakes (Missoula Floods). Rapid erosion, melting of ice sheets (jökulhlaups). Collapse of earthen barriers (landslides or glacial moraines). Collapse of volcanic dams created by lava flows, lahars, or pyroclastic flows. Overtopping of earthen or rock barriers Lake overtopping (e.g., Lake Bonneville). Ocean spilling over a dividing ridge into a landlocked basin (e.g., Zanclean flood and Black Sea flood). A smaller scale example would be the Pantai Remis landslide. Examples Examples where evidence for large ancient water flows has been documented or is under scrutiny include: Overflow of lakes formed by landslides An example is the lake overflow that caused one of the worst landslide-related disasters in history on June 10, 1786. A landslide dam on Sichuan's Dadu River, created by an earthquake ten days earlier, burst and caused a flood that extended downstream and killed 100,000 people. Postglacial rebound Postglacial rebound changes the tilt of ground. In lakes, this means that shores sink in the direction farther away from the former maximum depth of