Sturgeon Lake Caldera facts for kids

The Sturgeon Lake Caldera is a very old and large extinct volcano in Northwestern Ontario, Canada. It is located in the Kenora District. An extinct volcano means it will not erupt again.

This special place is one of the best-preserved calderas in the world. A caldera is a big, bowl-shaped hollow that forms when a volcano collapses after a huge eruption. The Sturgeon Lake Caldera is about 2.7 billion years old! It stretches for at least 30 km (19 mi).

What is the Sturgeon Lake Caldera?

This ancient caldera is like a giant puzzle made of different rock layers. These layers include volcanic rocks (from eruptions), sedimentary rocks (from bits of other rocks and minerals), and intrusive rocks (formed underground).

The caldera formed underwater a very long time ago. It has nearly 3,000 m (9,843 ft) of rock layers that filled up the collapsed volcano. Sometimes, there were huge explosions of felsic magma, both underwater and above water. These explosions created special rocks called rhyodacitic and rhyolitic tuffs.

How Big is This Ancient Volcano?

The Sturgeon Lake Caldera is part of a larger area called the Wabigoon greenstone belt. The volcanic rocks from this caldera spread out over 30 km (19 mi) from east to west.

Inside the caldera, there are at least five major layers of ash flow tuff. These layers are like blankets of ash and rock from ancient eruptions. They can be from 100 m (328 ft) to 1,200 m (3,937 ft) thick!

One of the biggest eruptions created a layer called the Mattabi pyroclastic flow. This layer is over 800 m (2,625 ft) thick and stretches for at least 30 km (19 mi). This huge eruption also helped create a large mineral deposit called the Mattabi massive sulfide deposit. This deposit formed on and under the ancient seafloor.