Lassen Peak
Lassen Peak, commonly referred to as Mount Lassen, is a lava dome volcano in Lassen Volcanic National Park in Northern California. Located in the Shasta Cascade region above the northern Sacramento Valley, it is the southernmost active volcano in the Cascade Range of the Western United States, and part of the Cascade Volcanic Arc stretching from southwestern British Columbia to Northern California. It supports many flora and fauna among its diverse habitats, which reach high elevations and are subject to frequent snowfall.
Lassen Peak has a volume of, making it one of the largest lava domes on Earth. The volcano arose from the former northern flank of now-eroded Mount Tehama about 27,000 years ago, from a series of eruptions over the course of a few years. The mountain has been significantly eroded by glaciers over the last 25,000 years, and is now covered in talus deposits.
On May 22, 1915, a powerful explosive eruption at Lassen Peak devastated nearby areas, and spread volcanic ash as far as to the east. This explosion was the most powerful in a series of eruptions from 1914 through 1917. Lassen Peak and Mount St. Helens in Washington were the only two volcanoes within the contiguous United States to erupt during the 20th century.
Lassen Volcanic National Park, which encompasses an area of, was created to preserve the areas affected by the eruption for future observation and study, to protect the nearby volcanic features, and to keep anyone from settling too close to the mountain. The park, along with the nearby Lassen National Forest and Lassen Peak, have become popular destinations for recreational activities, including climbing, hiking, backpacking, snowshoeing, kayaking, and backcountry skiing. Lassen Peak is dormant, meaning the volcano is merely inactive, and it has a functioning magma chamber under the ground still capable of eruptions. Thus it poses a threat to the nearby area through lava flows, pyroclastic flows, lahars, ash, avalanches, and floods. To monitor this threat, Lassen Peak and the surrounding vicinity are closely observed with sensors by the California Volcano Observatory.
Geography
Lassen Peak lies within Lassen Volcanic National Park, in Shasta County, California, east of the city of Redding. Lassen Peak and the rest of the National Park area are surrounded by the Lassen National Forest, which has an area of. Nearby towns include Mineral in Tehama County and Viola in Shasta County.Lassen Peak reaches an elevation of, according to 1992 data from the U.S. National Geodetic Survey; 1981 data from the Geographic Names Information System lists the mountain's elevation at. Lassen Peak marks the southernmost major volcano in the Cascade Range, rising above the northern Sacramento Valley. Bounded by the Sacramento Valley and the Klamath Mountains to the west and the Sierra Nevada mountain range to the south, it is the second tallest peak in the California segment of the Cascades, behind the Mount Shasta, which lies to the north. Due to its proximity to nearby volcanoes Mount Tehama and Mount Diller, it is not easy to distinguish from its neighboring peaks.
Physical geography
Lassen Peak has the highest known winter snowfall amounts in California, with an average annual snowfall of ; in some years, more than of snow falls at its base elevation of at Lake Helen. The Lassen Peak area receives more precipitation than anywhere in the Cascade Range south of the Three Sisters volcanoes in Oregon. Though the volcano lies too far to the south to support a permanent snow cover over the entire mountain, the heavy annual snowfall on Lassen Peak creates fourteen permanent patches of snow on and around the mountain top, but no glaciers.Lightning has been known to strike the area frequently during summer thunderstorms. These can initiate fires. On July 23, 2012, a lightning strike started the Reading Fire to the northeast of the Paradise Meadow region, which was contained after it reached an area of. During the summer and fall of 2016, the National Park Service carried out prescribed fires to help reduce the amount of fuel available for fires in the Mineral Headquarters area and the Manzanita and Juniper Lake areas, respectively.
Climate
Ecology
Lassen Peak supports a variety of flora that include mountain hemlock, whitebark pine, and alpine wildflowers. Mountain hemlocks generally only reach an elevation of, while whitebark pines reach up to. Throughout the national park, forests can be found featuring red fir, mountain alder, western white pine, white fir, lodgepole pine, Jeffrey pine, ponderosa pine, incense cedar, juniper, and live oak. Other plants found in the Lassen Peak area consist of coyote mint, lupines, mule's ears, ferns, corn lilies, red mountain heathers, pinemat manzanitas, greenleaf manzanitas, bush chinquapins, catchflies, Fremont's butterweed, buckwheat, granite gilia, mountain pride, mariposa tulips, creambush, and a variety of chaparral shrubs.The various habitats in the Lassen Volcanic National Park support about 300 vertebrate species such as mammals, reptiles, amphibians, fish, and birds, including bald eagles, which are listed as Threatened under the Endangered Species Act of 1973, and peregrine falcons, which were removed from the endangered species list in 1999. In forested areas below, animals include American black bears, mule deer, martens, brown creepers, mountain chickadees, white-headed woodpeckers, long-toed salamanders, and several bat species. At higher elevations, Clark's nutcrackers, deer mice, and chipmunks can be found among mountain hemlock stands, and subalpine zones with sparse vegetation host populations of gray-crowned rosy finches, pikas, and golden-mantled ground squirrels. Among scattered stands of pinemat manzanita, red fir, and lodgepole pine, animals include dark-eyed juncos, montane voles, and sagebrush lizards. Meadows at the bottoms of valleys along streams and lakes support Pacific tree frogs, Western terrestrial garter snakes, common snipe and mountain pocket gophers. Other animals found within the national park area include snakes such as rubber boas, common garter snakes, and striped whipsnakes; cougars; amphibians like newts, salamanders, rough-skinned newts, and Cascades frogs; 216 species of birds including MacGillivray's warblers, Wilson's warblers, song sparrows, spotted owls, northern goshawks, and bufflehead ducks; five species of native fish that include rainbow trout, tui chubs, speckled daces, Lahontan redsides, and Tahoe suckers; and four invasive fish species including brook trout, brown trout, golden shiners, and fathead minnows. Prominent invertebrate species include California tortoiseshell butterflies.
Geology
Lassen Peak lies near the southern end of the Cascade Volcanic Arc, at the western edge of the Basin and Range Province. Like other Cascade volcanoes, it was fed by magma chambers produced by the subduction of the oceanic Juan de Fuca tectonic plate under the western edge of the continental North American tectonic plate. The region is also affected geologically by the Cascadia subduction zone, which dips eastward beneath the western coast of North America in the Pacific Northwest, as well as horizontal stretching to the east of crustal rock in the Basin and Range Province. About 3 million years ago, the southern limit of active volcanoes in the Cascades corresponded to the Yana Volcanic Center to the south of Lassen Peak, but currently the southern edge of the Lassen Volcanic National Park now marks the same border, indicating that the Cascade Arc's southern end migrates at a rate of annually.In the southern segment of the Cascades, volcanoes exhibit widespread and long-lived activity produced by magma that ranges from low-silica basalt to siliceous rhyolite. The Lassen volcanic center is fed by two magma chambers, one calc-alkaline reservoir common to the rest of the Cascade Volcanoes, and the other a smaller volume of low-potassium olivine tholeiitic basalt associated with the Basin and Range province. Within the region, most if not all of the volcanic rock has erupted in the past 3 million years. During this period, at least five large andesitic stratovolcanoes formed in the vicinity of Lassen Volcanic National Park, building volcanic cones before going extinct and undergoing erosion. For most volcanic centers in the Southern Cascades, one volcano becomes active and normally becomes extinct as another begins to erupt, but at the Lassen locus, the Maidu and Dittmar volcanic centers overlapped during the late Pliocene to the early Pleistocene. Volcanism within the Lassen vicinity follows a trend of intermittent, episodic eruptions punctuating long periods of dormancy, a pattern which persisted through the late Pleistocene and Holocene. During the past 825,000 years, the area has produced hundreds of explosive eruptions over an area of, and the past 50,000 years have seen seven major silicic eruptive episodes that produced dacitic lava domes, tephra, and pyroclastic flows, along with five periods of basaltic and andesitic lava flows.
Local activity began 600,000 years ago with the formation of Brokeoff Volcano. Around the same time, about 614,000 years ago, an explosive eruption southwest of Lassen Peak produced of pumice and ash, covering the area between the vent and what is now the city of Ventura, California. This deposit, referred to as the Rockland tephra, reaches up to several inches in thickness within the San Francisco Bay area, and can be found as far as northern Nevada and southern Idaho. The same eruption also formed one of three known calderas within the Cascade, the others being Crater Lake and the Kulshan Caldera at Mount Baker. Shortly after, the Lassen volcanic center, a cluster of closely spaced volcanoes, formed in the area, covering the nearby caldera. During the late Pleistocene it produced andesite lava flows that built the Brokeoff composite volcano. Following the end of volcanism at Brokeoff Volcano hydrothermal fluids began chemically weathering minerals in the andesite flows, altering the once strong rocks into easily eroded materials. Glaciers and streams were able to rapidly erode deep channels into these altered volcanic rocks, reducing the once lofty peak of Brokeoff Volcano into the landscape we see today. Following the erosion of Brokeoff Volcano, volcanism migrated to the Lassen Domefield to the northeast.
Lassen Peak's lava dome formed about 27,000 years ago from a series of eruptions over a few years, undergoing significant glacial erosion between 25,000 and 18,000 years ago. The bowl-shaped depression on the volcano's northeastern flank, called a cirque, was eroded by a glacier that extended out from the dome. By 18,000 years ago, Lassen Peak started to form a mound-shaped dacite lava dome, pushing its way through Tehama's former northern flank. As the lava dome grew it shattered overlaying rock, which formed a blanket of angular talus around the emerging steep-sided volcano. Likely resembling the nearby 1,100-year-old Chaos Crags, Lassen Peak reached its present height in a relatively short time, probably in just a few years. Within the past 1,000 years or so, activity at Lassen Peak has produced six dacite lava domes, erupted tephra and pyroclastic flows, and built Cinder Cone and the Fantastic Lava Beds. It also created the rockfalls at Chaos Jumbles.
The only active Cascade volcano with an elevation above that is not a stratovolcano, Lassen Peak is a rhyodacitic lava dome. It represents one of the largest lava domes on Earth, with a height of above its surroundings, and an approximate volume of. Unlike more conventional, conical stratovolcanoes like Mount Shasta or Mount Rainier, Lassen Peak is part of a volcanic center that erupts from different vents, which each remain active for a number of years or decades but often do not erupt from the same vent twice, also known as a monogenetic volcanic field. 2000 years after Lassen's formation, it was surrounded by glaciers which ate away at its spiny protrusions of dacite. Due to glacial erosion from the last local glacial advance, which ceased roughly 15,000 years ago, Lassen's lava dome is now covered in broken rock fragments at the base of crags called talus deposits. Only its crag formations on its southern flank, near the summit trailhead, have not been significantly altered by glacial erosion.