Huge Lava Flow
Geosites Map

North of Calumet Lake, the Greenstone Lava flow, largest by volume of the Lava flows of the Portage Lake Volcanics, runs through the area, making a slight ridge and cropping out at the surface. This is one of Earth’s largest lava flows. A “magma ocean” lasting more than 1000 years formed at the time of its eruption, and this feature covered an area at least as large as the western half of Lake Superior.

Greenstone Flow

It may surprise people that here in the UP,  far from active volcanoes, we find the world’s greatest known outpouring of lava, a great flood basalt, which led to the largest lava flows on Earth.  The outcrop at Calumet Lake is a typical one which represents the rock underlying Calumet.  There are more than 200 lava flows piled on top of each other, with the oldest located to the East the younger ones westward.  At this place you can see the tilted layers and the black color of basalt, the name we give to the most common type of lava on Earth and other planets.

Eastern Iceland


Flood basalts are the result of deep earth processes, events that probably originate in Earth’s outer core, a liquid layer of Earth which convects readily and heats the solid lower mantle. The lower mantle becomes hotter and more mobile, which results in mantle plumes that lead to partial melting of the upper mantle and Large Igneous Provinces (LIPs). Flood basalts are a big feature of LIPs.