Maar Lakes of Germany's Volcanic Eifel Region
What is the origin of the unique lakes in the Volcanic Eifel region of Germany? In short, they were created from an explosion of water vapour when lava from a hot spot under the region met with groundwater thousands of years ago. The explosion created a round funnel, or crater, with earthen walls, which was later filled with rainwater. That is why the water is really clear and has rather good visibility.