Oregon’s Crater Lake
Formed by the eruption of Mount Mazama over seven thousand years ago, Crater Lake in Oregon is now known as one of the most beautiful natural wonders in North America. It is particularly renowned for the limpid blue of its waters, which, according to Native American lore, transformed the mountain bluebird from grey to blue. Stretching to a depth of almost 2000 feet, the lake is the deepest in the United States and the tenth deepest in the world. This depth is due to the way in which it was formed out of a powerful volcanic eruption, which also accounts for its unique geological features and the towering cliffs which surround it. Mount Mazama, the volcanic peak upon which Crater Lake sits, is part of the Cascade Range of mountains which extends from British Columbia in Canada to northern California, passing through Washington and Oregon on the way. This is part of the Pacific Ocean’s Ring of Fire, an area of persistent geological upheaval which encircles the Pacific. The Cascade Range is thus an area of frequent volcanic activity, and has relatively recently witnessed the eruptions of two volcanoes: Lassen Peak in the early 20th century and, most recently, Mount St. Helens in 1980.
The eruption of Mount Mazama occurred in around 5677 BC, and was notable for being so ferocious that it completely destroyed the peak of the mountain and reduced its height by about 1 mile. Prior to the eruption Mount Mazama was around 12,000 feet tall, but after this reduction its highest point was the 8,000-foot tall Hillman Peak on the edge of Crater Lake. The force of the eruption itself is thought to have blown out around 50 km3 of magma, and covered the northwestern region of North America, from the Pacific coast to central Canada, with volcanic ash.
This highly destructive eruption accounts for the depth and circumference of Crater Lake, which sits in what is known as a caldera, a cauldron-like depression which can form in the wake of a volcanic eruption. A caldera is the result of the complete evacuation and collapse of a reservoir of magma. In the case of Mount Mazama, the eruption was so rapid and severe, with several vents pouring forth magma simultaneously, that the mountain collapsed under the weight of all the magma it had expelled. The surface of the mountain then fell into the magma chamber beneath, which had been emptied by the eruption. This created a sinkhole effect and left an immense bowl-shaped hollow on the surface which is now Crater Lake.
The area was devastated after the eruption, but it eventually cooled and rain and snow slowly filled the caldera, eventually forming the lake. Scientists estimate that it took around 720 years for the water levels to reach where they are today. This is still the way that lake water is renewed, since there are no rivers feeding it. The lack of tributaries makes the lake water some of the purest in the world, and accounts for the clarity of its blue colour. The only other input into the lake comes in the form of hydrothermal vents, which heat the deepest part of the lake, and which suggest that the volcano is still active and another eruption could one day occur.
The volcanic force which formed Crater Lake also left several notable geological features dotted around the lake and its surrounding area. These include the lake’s two islands, which are both remnants of eruptions. The largest of these, at around 315 acres, is Wizard Island, a volcanic cinder cone made out of the materials which build up around an erupting vent. Wizard Island shows evidence of this in the small crater which sits on the highest point of the island. It was given its mystical sounding name by William Gladstone Steel, the ‘father of Crater Lake’, who led the campaign to designate the area as a national park. He referred to the crater atop the island as the ‘Witches Cauldron’. The second island in the lake is known as the Phantom Ship, and is much smaller than Wizard Island at only 500 feet in width and 200 feet in length. This island is a natural rock formation made of the volcanic rock andesite. Its origins as a volcanic excrescence are apparent in the jagged, uneven terrain of the island, which, particularly in low light, make it look like a ghost ship, which inspired its similarly spooky name.
One other unique feature which the lake is known for is the ‘Old Man of the Lake’, the white stump of a tree which has been floating vertically in the lake since at least 1896. This tree extends about 4 feet above the water line and is only 2 feet in diameter. It is thought that the low temperature of the lake has allowed the tree to remain there for so long without decomposing. A trip to visit the ‘old man’ is now an essential part of any tourist boat trip across the lake, although the tree’s constant movements make it hard to track. The lake is now one of the most popular tourist attractions in Oregon, and thanks to its status as a national park is a protected space. Its unique landscape, and the evidence it offers of the immense geological force which formed it, make it one of the most astonishing natural wonders in the United States.
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