maar

A broad, shallow, generally flat-floored volcanic crater of explosive origin that is often filled with water.

In geology:

A local German name originally applied to certain small crater-lakes in the recently extinct volcanic region of the Eifel, near Bonn, on the Rhine. The craters were believed to have resulted from explosive outbreaks, without emissions of lava.

Technically, any crater which has been produced by an explosion unaccompanied by lava.

a broad volcanic crater, usually filled with a lake

a flat-bottomed volcanic crater that was formed by an explosion; often filled with water