A volcanic subsidence crater (also called a pit crater or collapse crater) is formed when subsurface magma, supporting the rock overhead, drains away for whatever reason. The unsupported rock “ceiling” over the void left by the draining magma then collapses. (Much the same mechanism accounts for the formation of summit caldera craters, but those are typically at a larger scale.) A subsidence crater can be distinguished from other craters, such as maars (e.g., Soda Lakes in Nevada), or impact craters, because they have no built-up rim formed by debris ejected…
