The Ulmener Maar is a maar in the Eifel, close to the town of Ulmen in Rhineland-Palatinate. The meromictic lake is up to 37 meters deep and is surrounded by an average 20 meter high wall made of tuff rock that was formed from the ejecta of the former volcano. On the southern edge of the wall are the ruins of a knight's castle from the 11th century.
The Ulmener Maar has an irregular shape, measuring about 510 meters in a northwest-southeast direction and 250 meters across. The crater created by the volcanic eruption is up to 86 meters deep. Lower Devonian rocks are exposed on the crater walls above the water, and above that lies the tuff wall that surrounds the maar. The tuffs consist of volcanic ejecta material (pyroclastic sediments such as volcanic ash and lapilli) and rock shattered during the eruption.
The Ulmener Maar is considered to be the youngest of the Eifel maars, having only been formed after the eruption of the Laacher See volcano. Dating using varve chronology revealed an age of 11,000 years. However, the dating of organic remains at the base of the volcanic tuffs belonging to the maar using the radiocarbon method that has been carried out so far varies in the determined age between 7,335 and 10,920 years; based on further geological evidence, an age of around 9,500 years to a maximum of 12,400 years is assumed. Younger age values are only known for the Booser Doppelmaar, but here the dates are even further apart, between 6,275 and 35,240 years. The age of the Booser Doppelmaar is estimated at around 10,100 to 14,160 years. Volcanologists from the Smithsonian Institution place the last eruption of the Ulmen Maar between 8890 and 8590 BC.
The Jungferweiher, located north of the Ulmen Maar, is also a maar, but a silted-up one. Drilling has shown that it is the remains of a 118,000-year-old volcano that was much larger than the one from which the Ulmen Maar emerged. In 1942, the water was dammed on the swampy meadows, thus creating a body of water again, the northern part of which is now a bird sanctuary where rare and endangered birds can be observed. The lake also attracts many anglers because of its abundance of fish.
(Source: wikipedia)