When people think of volcanoes in the the state of Oregon, they tend to think of Mount Hood
which last erupted about 150 years ago. However, there are about a dozen other active volcanoes
within the state. One of these volcanoes was responsible for a recent cataclysmic eruption,
which was 119 times larger than the 1980 of Mount Saint Helens. The volcano in question
is known as Crater Lake, or Mount Mazama, and has erupted 5 times in the last 10,000 years.
This video will discuss this rather unique active volcano, and mention what its future hazards are.
For this video, we are defining an active volcano as any volcano or volcanic field which has erupted
in the last 10,000 years. Although 10,000 years may seem like a long timeframe, this is the
definition used by the global volcanism program. The crater lake volcano can be found in the
southwest central portion of the state of Oregon. Specifically, it is 55 miles
northeast of the town of Medford. Mount Mazama is part of the cascade mountain range,
and is today classified as a caldera volcano. Caldera volcanoes form in very rare eruptions
where a significant amount of a volcano's large magma chamber empties. Once the volcano is empty,
the weight of the above rock makes it collapse and fill what used to be a full magma chamber.
There are several overlapping volcanoes which formed the area of Crater Lake. The oldest of
these, Mount Scott, formed 420,000 years ago. Over the next several hundred thousand years, Mount
Scott and other nearby volcanoes became extinct, while new volcanoes grew to the west. By about
30,000 years ago, Mount Mazama began to generate increasingly explosive eruptions that were
followed by thick flows of silica-rich lava. which is a sign of an accumulation of a large volume of
highly explosive magma deep beneath the volcano. One such eruption which occurred in 5900 BC
produced a very thick layer of pumice and ash at Llao Rock. The size of this eruption was massive.
It had a VEI rating of 6 and was 24 times larger than the 1980 eruption of Mount Saint Helens.
However, the largest eruption was yet to come. About 7700 years ago, the center of what is now a
large lake contained a 12,000 foot tall volcano. Today, the crater lake shoreline is about 6200
feet. What happened? A single eruption of a truly unimaginable size caused the mountain to lose a
mile of elevation and formed the 5 mile or 8 kilometer wide crater lake which we see today.
During a period of about 6 hours in 5680 BC, the volcano explosively erupted in what was
the largest cascade mountain eruption in the last million years. This eruption covered a
large portion of southern Canada and the northwest portion of the United States with a layer of ash.
The only way to show the size of this eruption is via a comparison.
This eruption was 119 times larger than the 1980 of Mount Saint Helens, 7100 times larger than
the 1915 eruption of Lassen Peak, and about 2.5 times larger than the 1883 eruption of Krakatoa.
After this caldera forming eruption, a number of smaller eruptions occurred. The vast majority of
these features have a peak beneath the current lake. The only recent eruptive feature above
the lake is the wizard island cinder cone, which can be found on the western portion of the lake.
For the last 4800 years, no additional eruptions have occurred from this volcano. This does NOT
mean that crater lake is extinct, however. Every few years, a number of low intensity earthquakes
caused by volcanic activity take place beneath the volcano. Do not be worried. An eruption
here is not likely for the next several hundred years, if not longer. Any future eruption would be
explosive, and create pyroclastic flows, lahars, and emit large amounts of ash into the atmosphere.
Due to these hazards, in the most recent volcano hazard assessment from the US Geological Survey,
the Crater Lake volcano was rated as a very high threat volcano. Its eruptions are
infrequent but can be very large in size. I hope that you enjoyed this video. If
you would like to request a specific topic, please leave a comment below.