The 10,900-years-old Ulmener Maar is the youngest volcano in Germany. If we imagine the whole of the Earth’s history compressed into 24 hours, it is only a moment ago that hot magma was rising up from 60 kilometres below the Earth’s surface here. That which gets going slowly and sluggishly to start with, suddenly becomes highly explosive! As soon as magma from inside the Earth comes into contact with groundwater, there are almighty explosions, in which all the water suddenly turns into steam.
The violent shock waves from these explosions break up the surrounding rock which is ejected from the mouth of the volcano and then builds up a circular rim of loose volcanic rock (tephra) on the surface.
The layers of rock above the space which has been emptied by the explosion collapse, creating a typical funnel-shaped maar. As everything calms down, the crater begins to fill with groundwater and water from precipitation. So a maar lake is formed. Typically, maars are hollow basins lower than the surrounding land surface. Beyond the church, just a few metres from here, it is easy to make out layers of rock which were ejected during the eruption.