Ever see Crater Lake and wonder how it came to be? If you haven’t, great, because that’s why I’m here. If you’ve ever been lucky enough to see it, either by visiting or flying over it on your way to Seattle, it’s hard not to recognize how beautiful this volcano is.
That’s right, Crater Lake was once a volcano. But it looks like a lake, so how can it be a volcano? Crater Lake is what geologists call a caldera, which is a volcano that has collapsed after a particularly explosive eruption, and one that destabilizes its center. To be considered a caldera, however, a volcano simply can’t have a gaping hole where there once was a volcano. It needs to be at least a kilometer across, any smaller and it’s known as a “collapse pit”.
Since there are more than one kind of volcano, there are several ways a caldera can form, depending on that particular volcano. The first scenario requires a composite volcano’s summit to collapse after a large silica-rich eruption (which is the case of Crater Lake, so we’ll get more into that soon). The second scenario is found in Hawai’ian volcanoes, where the top of a low shield volcano collapses due to underground drainage from the main magma chamber. The last scenario is found in extremely large volcanoes, like Yellowstone. The area collapses after enormous amounts of silica-rich pumice and ash are emptied from the volcano during an eruption, forming a ring of fractures around the area.
Now that you’re more familiar with calderas and how they can form, you have a better understanding of Crater Lake. Feels good, doesn’t it?
Crater Lake itself formed from the collapse of Mt. Mazama, after an eruption that caused the summit to collapse about 7,000 years ago. The eruption emptied 50-70 square kilometers of pyroclastics, seriously destabilizing its structure. After its collapse rainwater and snow runoff collected in its crater. Later, more minor eruptions formed the small (relatively speaking, of course) dome inside the caldera, adorably named Wizard Island. Today, Crater Lake is 10 kilometers across, and 1175 meters deep (96-97).
It’s hard to keep Oregon weird with something so interesting and breathtaking. But keep it weird anyway, and go visit Crater Lake, my dear readers.
Volcanism 