The Eifel region lies roughly between the cities of Aachen, Trier and Koblenz, in west-central Germany. It is home to many ancient volcanic features, including the circular lakes known as maars. Maars are the remnants of violent volcanic eruptions, such as the one that created Laacher See, the largest lake in the area. The explosion that created the lake is thought to have occurred around 13,000 years ago.
For more details, please refer to
https://www.gpsworld.com/research-roundup-gps-reveals-volcanic-activity-under-europe/