What's the term for a large depression formed when a volcano erupts and collapses?
And the answer: a caldera.
According to National Geographic, during a volcanic eruption, magma that's in the magma chamber underneath the volcano is expelled, often forcefully. When the magma chamber empties, the support that the magma had provided inside the chamber disappears. As a result, the sides and top of the volcano collapse inward.
If you've ever been to Yellowstone National Park, Crater Lake, or Valles Caldera National Reserve, chances are you've laid eyes on these magnificent post-eruption formations. Thousands of years ago, violent eruptions emptied volcanic chambers to create calderas, often deep depressions in a once-solid rock foundation. Calderas can form lakes or other bodies of water, as the bowl-shape promotes the collection of rainwater. In fact, Oregon's Crater Lake – a caldera that formed after the eruption of Mt. Mazama thousands of years ago – is now the deepest lake in the United States.
While most calderas form after a dramatic explosion of lava, they can form from less intense eruptions, too. Slower eruptions often occur in shield volcanoes, which tend to be flatter and more sloped. Over time, lava flows outward to create a series of nested calderas, as seen in the Kilauea Volcano in Hawai'i.
Resurgent calderas also represent another post-volcanic structure on our Earth. These calderas are the largest of the bunch, and form after the widespread collapse of large magma chambers. Resurgent calderas are produced from the destructive eruptions known as pyroclastic sheet flows. The Toba Caldera on the Indonesian island of Sumatra is the newest resurgent caldera, created roughly 74,000 years ago by the largest volcanic eruption in the last 25 million years.
Did you know?
Earth isn't the only planet with calderas. Other planets, such as Venus and Mars, have calderas atop shield volcanoes and on widespread lava plains. Even our moon has calderas!