Laacher See

Long ago, a volcano here erupted. It threw out lots of ash and rock.

Then the ground sank into a big hollow. Water from under the ground filled it up.

The Laacher See volcano last erupted about 13,000 years ago. Scientists describe several explosive phases, and the opening it erupted from moved during the eruption. In all, it threw out around 20 cubic kilometers of ash and rock fragments, called tephra.

The eruption emptied the underground magma chamber, and the ground above it collapsed. This made a caldera, a large sunken hollow, which then filled with groundwater to become the lake.

Reinig and colleagues (Nature, 2021) rank the Laacher See eruption among Europe's largest volcanic events of the Upper Pleistocene, expelling around 20 km³ of tephra. An abstract by Albers and colleagues (EGU General Assembly, 2025) describes phreatomagmatic and Plinian phases, vent migration and collapse of the magma chamber, forming a caldera that subsequently filled with groundwater.

Seismic reflection profiles and multibeam mapping from surveys in 2019 and 2021 show two vent-shaped subbasins within the caldera depression, mostly filled with layered sediment that reaches at least 50 m in the northernmost subbasin. Four sediment cores taken in 2019 and 2023, 3.5 to 8.5 m long, will help reconstruct how the lake filled in.

Ash from the volcano blew far away. Some fell as far away as Italy.

Scientists studied old trees buried by the ash. The trees told them when it happened.

Ash from the eruption drifted as far as northern Italy and Saint Petersburg in Russia. Where it settled, it left a layer that scientists can recognize on land and in lake mud, so it works like a date stamp across Europe.

In 2021, scientists studied birch and poplar trunks buried by the eruption near the crater. Using tree rings and radiocarbon dating, they dated it to about 13,000 years ago, more than a century earlier than previously accepted. The eruption came about 200 years before a cold period called the Younger Dryas began, and the scientists say this rules out a direct link between the eruption and that cooling.

Laacher See tephra fell as far as northern Italy and Saint Petersburg, forming a distinctive marker bed in land and lake records. Reinig and colleagues (2021) used dendrochronology and radiocarbon measurements of three birch and two poplar trunks buried by pyroclastic deposits near the crater to date the eruption to 13,006 ± 9 calibrated years before present (taken as AD 1950), more than a century earlier than the previously accepted 12,880 ± 40 years from the Meerfelder Maar varve record.

Because the eruption lies about 200 varve-counted years before the Younger Dryas, the new date moves that cold interval's onset to 12,807 ± 12 calibrated years before present. The authors say their results preclude a direct link between the eruption and the Greenland Stadial-1 cooling.

Bubbles rise from the bottom of the lake. They are made of a gas called carbon dioxide.

Scientists listened to the bubbles with an underwater microphone.

Gas still seeps from the floor of Laacher See and from the ground along its shores. Scientists say the gas is about 99% carbon dioxide and comes from deep inside the Earth, from the upper mantle.

In August 2019, a team of 13 scientists spent three days on the lake. They used echo sounders, which send sound into the water, to map rising bubble plumes, and they lowered a hydrophone, an underwater microphone, to record the sound of the bubbles.

Jentsch and colleagues (EGU General Assembly, 2026) report gas seepages at depths of 8 to 52 m in the lake, some reaching the surface, plus mofettes and soil degassing on land; the gas is about 99% CO₂, with helium isotope ratios (above 5 Ra) pointing to an upper-mantle origin. Lake-wide flux campaigns in 2024 and 2025 found winter CO₂ emissions an order of magnitude higher than summer ones, suggesting that dissolved CO₂ builds up in the deep water while the lake is stratified, for about eight months a year.

In August 2019, a 13-member team (Eos, 2020) mapped bubble flares with multibeam echo sounders and recorded the bubbles with a hydrophone: they radiated energy below 5 kilohertz, like bubbles in other volcanic lakes.

Many ducks rest on the lake in winter. Grebes raise their young there too.

Reeds and trees grow along the shores.

Laacher See is protected as a European bird area. Rhineland-Palatinate's official data sheet for the area says its wide open water, shallow shores, reed beds and shoreline trees are the most valuable part of the nature reserve for birds. In the north of the state, it is one of two important places where swimming birds, especially diving ducks, rest and spend the winter.

The data sheet lists tufted ducks, pochards, goldeneyes, coots and many gulls, and great crested grebes breed on the lake.

The lake is the Natura 2000 bird protection area DE5509401 'Laacher See', designated in 2004; Rhineland-Palatinate's standard data sheet gives 354 ha, 92% of it inland water. It calls the extensive water surface with shallow shores, reed beds and shoreline trees the ornithologically valuable core of the nature reserve, and one of two important resting and wintering sites for waterbirds, especially diving ducks, in the north of the state.

Species on the sheet include tufted duck (Aythya fuligula), common pochard (Aythya ferina), common goldeneye (Bucephala clangula), Eurasian coot (Fulica atra) and black-headed gull, with great crested grebes (Podiceps cristatus) listed as breeding. People changed the lake too: KuLaDig records that two tunnels, one in the Middle Ages and another in the 19th century, lowered its level to win farmland.

Stay on the paths around the lake. Follow the signs.

Watch the ducks quietly from the shore.

Scientists keep a close watch on Laacher See. The GFZ Helmholtz Centre for Geosciences says the area is monitored by several stations that track gases and earth tremors, and in 2024 and 2025 scientists measured how much carbon dioxide the whole lake gives off.

PlayOwl's advice: stay on marked paths, follow any signs near places where gas comes out of the ground, and watch the birds from the shore without disturbing them, especially in winter when they are resting.

The GFZ Helmholtz Centre for Geosciences notes that the region around Laacher See shows CO₂ degassing and is monitored by several fluid-monitoring and seismological stations. Jentsch and colleagues (2026) explain that their lake-wide CO₂ flux campaigns are part of an ongoing monitoring study, because gas stored in the deep water during stratification could be released suddenly by a disturbance such as an earthquake or a landslide.

PlayOwl's own advice for visitors: keep to marked paths, follow posted signs near gas vents, and give resting waterbirds space, since the data sheet describes the lake as an important resting and wintering site.