Соққан Техама жанартауы: Каскад жотасының тарихы

Eroded Andesitic stratovolcano in Northern California

Mount Tehama (also called Brokeoff Volcano or Brokeoff Mountain) is an eroded andesitic stratovolcano in the Cascade Volcanic Arc and the Cascade Range in Northern California. Part of the Lassen volcanic area, its tallest remnant, Brokeoff Mountain, is itself the second highest peak in Lassen Volcanic National Park and connects to the park's highest point, Lassen Peak. Located on the border of Tehama County and Shasta County, Brokeoff's peak is the highest point in the former. The hikers that summit this mountain each year are treated to "exceptional" views of Lassen Peak, Roosevelt had been told that the area was actually extinct in terms of eruptive activity. Despite assurance from Native Americans in the area that the mountain was indeed active, settlers continued to think that Lassen Peak was extinct and "dead" and so continued to settle nearby. The natives continued to declare that "one day the mountain would blow itself to pieces". Brokeoff Volcano represents the Pleistocene component of the Lassen volcanic complex, an area of active volcanism for more than three million years. It formed during a period of eruptive activity approximately 600,000 years ago on a series of faults; the largest of these eruptions was about 50 times as powerful as the 1980 eruption of Mount St. Helens. During the Pleistocene, constantly renewed lava of andesite flowed from the central vent of the volcano. The eruption of overlapping andesitic lava flows accumulated to build the volcano. By the time it reached its peak size, the volcano was immense, measuring at its base between and wide and more than 3352.80 m tall. Activity at Brokeoff lasted for approximately 200,000 years. Eruptions varied from ejection of pyroclastic material to andesitic lava flows built primarily of feldspar, pyroxene, and olivine. Brokeoff's remains are exposed to the southwest Mount Lassen in Shasta County, California. Sulphur Works, an area known for its sharp, putrid scent, is thought to be the center of the ancient volcano. The central vent of Brokeoff Volcano was located near modern Diamond Peak. After volcanism at Brokeoff ended, magmatism became more silicic and began migrating toward Lassen Peak's northern flank. The last 400,000 years have seen at least three known flows, parts of which are still on Raker Peak and Mount Conard. A subsequent explosive eruption ejected of material and created a large crater, which was soon covered by lava. Twelve lava domes were built throughout the area and the next period of eruptive activity began. Spanning 50,000 years it ejected to of material and was followed by a third period. At least twelve periods of activity have taken place since Brokeoff formed, consisting of activity including pyroclastic flows, pasty lavas, and additional lava domes.

Near the trailhead at lower elevations, alder thickets are present, as well as incense cedar, red firs, and western white pine. At higher elevations, groups of mountain hemlock and lupines prevail.

Hiking is especially popular on the mountain during summer. The mountain trail lasts between four and six hours, spans , and offers "exceptional" views of Mount Diller, Lassen Peak, Chaos Crags, and Mount Conard. Due to the characteristically intermittent eruptions of active volcanoes such as Lassen Peak, there is some threat from the volcanoes of the LVNP. Dacitic explosive eruptions have taken place within the last 50,000 years at Lassen Peak, Chaos Crags, and Sunflower Flat, and effusive eruptions of basalt have occurred at Tumble Buttes, Hat Mountain, and Prospect Peak. Pyroclastic flows and lahars could easily occur near glaciated areas and in river valleys like Hat Creek Valley. In addition to the volcanic hazards that could possibly occur, one volcano did erupt in the 20th century in LVNP: (Lassen Peak). Lassen's eruptions (1914–21, though most activity occurred between 1914 and 1917) were very small compared to the 1980 eruption of Mount St. Helens.