Viti maar in Iceland is associated with Krafla volcano near Lake Myvatn area. White matter in the foreground is snow. Snow is common in Iceland even during summer months. Two people on the opposite rim for scale.
Maar is a specific type of volcanic crater. They are created by powerful volcanic explosions which almost instantly create a circular hole which is later filled with groundwater. Groundwater is a very important component in this process as it is the reaction between rising hot magma and groundwater that gives so much explosive power to this process. Such a volcanic eruption is known as phreatomagmatic eruption. Created hole fills with water and becomes a crater lake.
Viti maar in northwestern Iceland is a superb location for hiking and photographing. This maar is geologically very young, dating from 1724.