's eruption timeline, an example of caldera formation
A caldera is a large
depression that forms following the evacuation of a
magma chamber/reservoir. When large volumes of magma are erupted over a short time period, structural support for the crust above the magma chamber is lost. The ground surface then collapses downward into the partially emptied magma chamber, leaving a massive depression at the surface (from one to dozens of kilometers in diameter). Although sometimes described as a
crater, the feature is actually a type of
sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Only seven known caldera-forming collapses have occurred since the start of the 20th century, most recently at
Bárðarbunga volcano in Iceland.