maar

n. volcanic crater made by an explosion

A maar is a broad, low relief crater that is caused by a phreatic eruption or explosion caused by groundwater contact with hot lava or magma. The maar typically fills with water to form a relatively shallow crater lake. The name comes from a local German dialect of Daun, which is in turn derived from Latin mare (sea). Maars are shallow, flat-floored craters that scientists interpret have formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep erosion of a maar presumably would expose a diatreme. Maars range in size from to across and from to deep, and most are commonly filled with water to form natural lakes. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme.
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Noun
1. a flat-bottomed volcanic crater that was formed by an explosion; often filled with water
(hypernym) volcanic crater, crater

conj. but

n. battleship

conj. but, only

adv. only, solely, however

conj. mere

but, however, nevertheless, yet