Super volcanoes and deep lakes...................and a river gorge a group of explorers found in the very early 19th century....................sent by Pres. Jefferson..........................ostensibly to find the nw passage............

Geology[edit]

For more details on this topic, see Mount Mazama.

Relief map of the Crater Lake area

Volcanic activity in this area is fed by subduction off the coast of Oregon as the Juan de Fuca Plate slips below the North American Plate (see plate tectonics). Heat and compression generated by this movement has created a mountain chain topped by a series of volcanoes, which together are called the Cascade Range. The large volcanoes in the range are called the High Cascades. However, there are many other volcanoes in the range as well, most of which are much smaller.

About 400,000 years ago, Mount Mazama began its existence in much the same way as the other mountains of the High Cascades, as overlapping shield volcanoes. Over time, alternating layers of lava flows and pyroclastic flows built Mazama's overlapping cones until it reached about 11,000 feet (3,400 m) in height.

As the young stratovolcano grew, many smaller volcanoes and volcanic vents were built in the area of the park and just outside what are now the park's borders. Chief among these were cinder cones. Although the early examples are gone—cinder cones erode easily—there are at least 13 much younger cinder cones in the park, and at least another 11 or so outside its borders, that still retain their distinctive cinder cone appearance. There continues to be debate as to whether these minor volcanoes and vents were parasitic to Mazama's magma chamber and system or if they were related to background Oregon Cascade volcanism.

After a period of dormancy, Mazama became active again. Then, around 5700 BC, Mazama collapsed into itself during a tremendous volcanic eruption, losing 2,500 to 3,500 feet (760 to 1,070 m) in height. The eruption formed a large caldera that, depending on the prevailing climate, was filled in about 740 years, forming a beautiful lake with a deep blue hue, known today as Crater Lake.^[5]

The eruptive period that decapitated Mazama also laid waste to much of the greater Crater Lake area and deposited ash as far east as the northwest corner of what is nowYellowstone National Park, as far south as central Nevada, and as far north as southern British Columbia. It produced more than 150 times as much ash as the May 18, 1980 eruption of Mount St. Helens.

This ash has since developed a soil type called andisol. Soils in Crater Lake National Park are brown, dark brown or dark grayish brown sandy loams or loamy sands which have plentiful cobbles, gravel and stones. They are slightly to moderately acidic and their drainage is somewhat excessive.

Climate[edit]

November panoroma from Rim Village. During the winter, the road up to Rim Village is normally plowed butRim Drive is closed.

Snow is relatively rare at low elevations in western Oregon, but it is common at higher elevations, especially at Crater Lake. Measurements at park headquarters, 6,475 feet (1,974 m) above sea level, show that snow falls more often here than at any other long-term weather station in Oregon. Winter, which typically begins at the park in September and runs through June, includes an average of 98 days with measurable snowfall. Up to 37 inches (94 cm) of snow have fallen on the park in a single day (in 1937, 1951, and 1971), 313 inches (800 cm) in a month (January 1950), and 903 inches (2,290 cm) in a year (1950).^[6]

Snow typically accumulates in the park to depths of 10 to 15 feet (3.0 to 4.6 m) by early spring. Most of the park's roads remain closed through late spring, and snow lingers into the summer. In July and August, snowfall is uncommon, and "one magnificent day typically follows another".^[7]

January is the coldest month, when highs average about 35 °F (2 °C) and lows average about 18 °F (−8 °C).^[8] August is the warmest month, with an average high of roughly 69 °F (21 °C) and an average low of about 40 °F (4 °C).^[8] Between 1962 and 1990, the highest recorded temperature was 90 °F (32 °C), and the lowest was −21 °F (−29 °C).^[9] Annual precipitation averages about 66 inches (1,700 mm) a year.^[10] December is the wettest, averaging about 11 inches (280 mm).^[10]

Although snow covers Crater Lake National Park for eight months of the year (average annual snowfall is 533 in (1,350 cm)), the lake rarely freezes over due in part to a relatively mild onshore flow from the Pacific Ocean. The last recorded year in which the lake froze over was in 1949, a very long, cold winter. A 95% surface freeze occurred in 1985. The immense depth of Crater Lake acts as a heat reservoir that absorbs and traps sunlight, maintaining the lake temperature at an average of 55 °F (12.8 °C) on the surface and 38 °F (3.3 °C) at the bottom throughout the year. The surface temperature fluctuates a bit, but the bottom temperature remains quite constant.