The Rodderberg is an extinct

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

in the east of the municipality of Wachtberg near

Bonn The federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300,000. About south-southeast of Cologne, Bonn is in the southernmost part of the Rhine-Ru ...

Germany Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...

. The last eruption was 250,000 years ago. It is situated just above the

Rhine The Rhine ; french: Rhin ; nl, Rijn ; wa, Rén ; li, Rien; rm, label=Sursilvan, Rein, rm, label=Sutsilvan and Surmiran, Ragn, rm, label=Rumantsch Grischun, Vallader and Puter, Rain; it, Reno ; gsw, Rhi(n), including in Alsatian dialect, Al ...

Valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...

. Together with the Drachenfels directly opposite, the Rodderberg narrows the Rhine Valley. This gorge portion is the southern limit of the lowland-bay of Cologne. The Rodderberg offers views to the

Siebengebirge The (), occasionally Sieben Mountains or Seven Mountains, are a hill range of the German Central Uplands on the east bank of the Middle Rhine, southeast of Bonn. Description The area, located in the municipalities of Bad Honnef and Königs ...

, the Rhine Valley and up to the

Cologne Cathedral Cologne Cathedral (german: Kölner Dom, officially ', English: Cathedral Church of Saint Peter) is a Catholic cathedral in Cologne, North Rhine-Westphalia. It is the seat of the Archbishop of Cologne and of the administration of the Archdiocese of ...

, about 50 km away.

Geology

The Rodderberg detonated in a

phreatomagmatic eruption Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

about 250,000 years ago. This happened when the magmatic plume reached the groundwater level of the Rhine (about 50m higher than today). After the explosion, the crater was filled with water that formed a

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

of about 90 m depth. In the last 250,000 years this feature filled with dust and soil until it was filled up to today's level. At present, all that is left of the old volcano is just a small hill that has a shallow concave shape. If one didn't know that it was a volcano, one would not recognize it. {{coord, 50, 38, 33, N, 7, 11, 54, E, region:DE_type:mountain, display=title Landforms of North Rhine-Westphalia Landforms of Rhineland-Palatinate Volcanoes of Germany Maars of Germany Extinct volcanoes Pleistocene volcanoes Nature reserves in Rhineland-Palatinate