Putting the ‘Crater’ in Crater Lake
By Kristin Strommer and Kevin Loder
UO Museum of Natural and Cultural History
Crater Lake is an Oregon treasure. The deepest freshwater lake in the United States, it is cradled at the heart of Mount Mazama in the southern Cascade Range. At about 6,000 feet above sea level, its sapphire-blue water is surrounded by dramatic cliffs rising up to 2,000 feet above the lake’s surface. As anyone who’s travelled there can tell you, Crater Lake is a scenic wonder.
But all this serene beauty has a very explosive past.
Do you ever wonder how Crater Lake was formed? Maybe it was created by a meteorite crashing into the Earth, leaving a big hole in the ground that later filled with water. Or perhaps glaciers carved out that big opening over millions of years. While these are good guesses, the ‘crater’ in Crater Lake is actually the result of a volcanic eruption – the most powerful eruption that the Cascade Range has seen in a million years.
8,000 years ago, there was no Crater Lake. In its place, Mount Mazama rose to about 12,000 feet above sea level. Around 7,700 years ago, Mazama violently erupted. Traditional Modoc and Klamath stories tell of an angry Spirit Chief who caused the eruption, sending molten avalanches down the sides of the mountain and into the surrounding valleys. Geologists tell us that the eruption also blew volcanic ash miles up into the sky. The eruption forced out so much volcanic material that Mazama’s magma chamber nearly emptied and its summit caved in, leaving behind a massive, smoking crater – called a “caldera” – that would eventually collect enough rain and snowmelt to form a lake.
Mount Mazama was a composite volcano, formed by layers and layers of lava that flowed out periodically over millions of years. These layers eventually stacked up to make a large, roughly cone-shaped mountain. While the summit disappeared thousands of years ago, many of the lava-flow layers can still be seen in the cliffs that make up Crater Lake’s rim.
The eruption of Mount Mazama was forty times more powerful than the 1980 eruption of Mount St. Helens in Washington. Volcanic ash burst from Mazama with such force that it landed as far away as central Canada. In more recent times, scientists have depended on Mazama ash to tell them about the timing of other events in Pacific Northwest history. For example, when archaeologists uncovered woven bark sandals in Oregon’s Fort Rock Cave, they could tell that the sandals were older than the eruption, since they were buried beneath a layer of Mount Mazama ash.
The eruption that formed Crater Lake’s crater was not an isolated event. Volcanic activity has been a feature of the Oregon landscape for millions of years, and it has continued to shape the Crater Lake area since the big eruption 7,700 years ago. Since that eruption, volcanic activity has occurred within the caldera itself, producing a cinder cone called Wizard Island, which is visible from the shore and accessible by boat. Most of the volcanic forms in the caldera, however, are under water and hidden from view.
Explore Crater Lake National Park and see for yourself. Everywhere you look, you’ll see evidence of volcanic activity and clues about the amazing events that have shaped – and continue to shape – Oregon’s landscape.
In the meantime, you and an adult can simulate a volcanic eruption at home!
Recipe for a Volcanic Eruption
You will need:
An empty soup can
¼ cup baking soda
A large measuring cup
Eruption mixture: 1 cup of water, ¾ cup of vinegar, 10 drops of yellow food coloring, and 10 drops of red food coloring.
Outside, make a mound of dirt as high as the soup can. Then place the soup can on top and form dirt around the can until it is shaped like a volcanic cone. Make sure the can is completely hidden by the dirt, with only the opening visible. Next, pour the baking soda into the can. Measure out all the parts of the eruption mixture into one large measuring cup. To start the eruption, add the completed eruption mixture into the soup can and watch lava pour from your erupting volcano!
Check out the brand new volcano and geology displays in the Museum of Natural and Cultural History’s Explore Oregon! exhibit, opening for a free family preview on the weekend of February 8 and 9. The museum is located at 1680 E. 15th Avenue, on the UO campus. Museum hours are Tuesday through Sunday from 11:00 a.m. to 5:00 p.m. Visit natural-history.uoregon.edu to learn more.