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132-398: Brokeoff Volcano was active from 590,000 to 387,000 years ago, during which period it erupted numerous flows with compositions ranging from basaltic andesite to dacite. At its peak, Brokeoff Volcano reached an estimated height of 3,350 metres (10,990 ft) and had a basal circumference of approximately 12 kilometres (7.5 mi). At approximately 313,000 years ago volcanism began shifting to

264-470: A 9-year-old boy died from a collapsed retaining wall along the summit trail on July 29, 2009, the path closed for six years for construction, reopening in 2015. The mountain's summit trail can be accessed from a parking lot on the northern side of the California State Route 89. The Lassen Peak Trail, which starts from this parking area, runs for 2.5 mi (4.0 km) with switchback turns,

396-585: A change from low-amplitude glacial cycles with a dominant periodicity of 41,000 years to asymmetric high-amplitude cycles dominated by a periodicity of 100,000 years. However, a 2020 study concluded that ice age terminations might have been influenced by obliquity since the Mid-Pleistocene Transition, which caused stronger summers in the Northern Hemisphere . Glaciation in the Pleistocene

528-484: A column that reached altitudes of more than 30,000 ft (9,100 m) and could be seen from the city of Eureka , 150 mi (240 km) to the west. This column underwent a partial collapse, generating a pyroclastic flow composed of hot ash, pumice, rock, and gas that destroyed 3 sq mi (7.8 km ) of land and spawned a lahar extending 15 mi (24 km) from the volcano and again reaching Hat Creek Valley. Smaller mudflows also formed on every side of

660-574: A deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another isotope ratio versus time. Ratios are converted to a percentage difference from the ratio found in standard mean ocean water (SMOW). The graph in either form appears as a waveform with overtones . One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials. According to this evidence, Earth experienced 102 MIS stages beginning at about 2.588 Ma BP in

792-421: A few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly and will continue to expand. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but evidence remains from

924-637: A haven for new settlers throughout the 1800s. Wagon trains followed winding trails on the Nobles Emigrant Trail which cut through the Lassen Peak vicinity near Sacramento Valley . One of the main landmarks along this trail was a volcano. Called Lassen Peak after Peter Lassen, a prominent blacksmith and guide who escorted California settlers, the volcano and the area around it were given merit for their gripping volcanic phenomena, which included lava beds and extinct volcanic cones. In May 1907, Lassen Peak

1056-468: 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 3.5 cu mi (15 km) to 6 cu mi (25 km) 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. Among

1188-425: A length of 1,000 ft (300 m). On May 14, 1915, Lassen Peak erupted lava blocks, which extended as far as Manton , 20 mi (32 km) west of the mountain. By the next day, the volcano had produced a dacitic lava dome, between 63 and 68 percent silica, which occupied its summit crater. On May 19, a large eruption destroyed this dome, and a new crater formed at the summit. No lava erupted, but parts of

1320-748: A lightning strike started the Reading Fire 1 mi (1.6 km) to the northeast of the Paradise Meadow region, which was contained after it reached an area of 28,079 acres (113.63 km ). 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. Lassen Peak supports

1452-400: A number of observers reported an eruption at Cinder Cone visible from more than 40 mi (64 km) away, with one observer near the mountain claiming to have observed a lava flow "running down the sides of the volcano." However, despite these testimonies and accounts in newspaper articles and several scientific journals, the veracity of these eruptions has been questioned by scientists from

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1584-535: A number of the potentially active Californian volcanoes reside less than 100 mi (160 km) from highly populated areas, and explosive eruptions could produce ash that travels for several hundred miles. In the case of signs that suggest impending volcanic activity, the United States Geological Survey has a plan in place to utilize portable monitoring instruments, deploy scientists to the area, and implement an emergency response plan developed by

1716-492: A region to the east of the Devastated Area. On May 30, 1914, despite an apparent lack of precursor earthquakes, Lassen became volcanically active again after 27,000 years of dormancy , when it produced a steam explosion that carved out a small crater with a fairly deep lake on the volcano's summit. The crater grew as it was carved by more than 180 similar phreatic explosions over the span of more than 11 months, reaching

1848-405: A round-trip hike 5 mi (8.0 km) in length that ascends approximately 2,000 ft (610 m) from the trailhead at 8,500 ft (2,600 m) to the summit at 10,457 ft (3,187 m). From the northeast summit, Lassen's 1915 mudflow and Prospect Peak are visible; the northwestern summit offers views of Lassen's two bowl-shaped craters and Mount Shasta, 80 mi (130 km) to

1980-421: 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 7 mi (11 km) 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

2112-526: A significant amount of snow and ice, these pyroclastic flows (or hot volcanic ash) might mix with water to form lahars (volcanically induced mudslides, landslides, and debris flows) that could destroy nearby communities. Dacitic eruptions could produce volcanic columns of gas and ash that could threaten aircraft in the area. Moreover, the Lassen volcanic center poses threats to visitors from sudden avalanches that could be entirely unrelated to eruptive activity. Due to

2244-576: A similar eruption today would threaten many lives and the northern Californian economy. Volcanic eruptions occur with similar frequency to major earthquakes from the San Andreas Fault , and at least 10 eruptions have taken place within the state during the past 1,000 years, the most recent at Lassen Peak. Under 1 percent of the state's population lives within hazard zones that could be affected by an eruption, but collectively hazard zones are visited by more than 20 million people each year. Moreover,

2376-413: A symmetrical pyroclastic cone. The youngest mafic volcano in the Lassen volcanic center, it is surrounded by unvegetated block lava and has concentric craters at its summit. Cinder Cone is comprised by five basaltic andesite and andesite lava flows, and it also has two cinder cone volcanoes, with two scoria cones, the first of which was mostly destroyed by lava flows from its base. In 1850 and 1851,

2508-568: A team of Russian scientists in collaboration with Princeton University announced that they had brought two female nematodes frozen in permafrost , from around 42,000 years ago, back to life. The two nematodes, at the time, were the oldest confirmed living animals on the planet. The evolution of anatomically modern humans took place during the Pleistocene. At the beginning of the Pleistocene Paranthropus species were still present, as well as early human ancestors, but during

2640-493: A variety of flora that include mountain hemlock , whitebark pine , and alpine wildflowers . Mountain hemlocks generally only reach an elevation of 9,200 ft (2,800 m), while whitebark pines reach up to 10,000 ft (3,000 m). 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

2772-765: Is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America , and several hundred in Eurasia . The mean annual temperature at the edge of the ice was −6 °C (21 °F); at the edge of the permafrost, 0 °C (32 °F). Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres (4,900–9,800 ft) thick, resulting in temporary sea-level drops of 100 metres (300 ft) or more over

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2904-454: Is no systematic correspondence between pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Only a few of the names for pluvials in restricted regions have been stratigraphically defined. The sum of transient factors acting at

3036-795: 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. The Lassen volcanic center includes Brokeoff Volcano, Lassen's dacitic lava dome, and a number of small andesitic shield volcanoes found northeast of Lassen Peak. The Lassen dome field includes 30 dacitic lava domes such as Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak; other major lava domes include Chaos Crags, Eagle Peak, Sunflower Flat, and Vulcans Castle. Nearby shield volcanoes include Prospect Peak and West Prospect Peak, and there are three cones close to Lassen Peak: Cinder Cone, Hat Mountain, and Raker Peak. The hydrothermal area inside

3168-453: 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

3300-438: Is sparse due to its siliceous (rich in silica), nutrient-deprived soil, which cannot sustain normal tree growth due to its lack of water retention. Due to their small size and thin deposits, the 1915 eruptions will likely not be well-preserved geologically. After 1915, steam explosions continued for several years, indicating extremely hot rock beneath Lassen Peak's surface. In May 1917, an especially strong steam explosion formed

3432-517: Is stored within the region, tectonic setting, and how hydrothermal systems evolve over long periods of time. GPS receivers have been in place to monitor deformation within the Lassen volcanic center since 2008, and 13 seismometers in the vicinity, first installed in 1976 and since updated each decade, continually survey earthquakes within the locale. The Lassen Volcanic National Park is visited by more than 350,000 people every year. Incorporating more than 150 mi (240 km) of hiking trails, it

3564-513: Is the geological epoch that lasted from c.  2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations . Before a change was finally confirmed in 2009 by the International Union of Geological Sciences , the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of

3696-550: Is visited by people looking to hike or backpack during the summers. Popular winter activities include snowshoeing and backcountry skiing . As the second-tallest volcano in Northern California, trailing only Mount Shasta, Lassen Peak is frequently visited by climbers and hikers from around the world. The summit opens for use most years near the end of June, remaining in use until heavy snow falls in October or November. After

3828-401: The 1980 eruption of Mount St. Helens , which had a volume of 0.24 cu mi (1.0 km ). The region on the volcano's northeastern flank destroyed by the eruptions, 3 sq mi (7.8 km ) in area, is now known as the Devastated Area, and it along with other deposits from the volcano has been altered by erosion and regrowth of vegetation, though the vegetation in Devastated Area

3960-638: The Alpine ice sheet on the Alps . Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were ice-covered. South of the ice sheets large lakes accumulated because outlets were blocked and the cooler air slowed evaporation. When the Laurentide Ice Sheet retreated, north-central North America was completely covered by Lake Agassiz . Over a hundred basins, now dry or nearly so, were overflowing in

4092-608: 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 0.6 cu mi (2.5 km ), making it one of the largest lava domes on Earth. The volcano arose from

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4224-848: The Endangered Species Act of 1973 , and peregrine falcons , which were removed from the endangered species list in 1999. In forested areas below 7,800 ft (2,400 m), 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

4356-718: The Geographic Names Information System lists the mountain's elevation at 10,457 ft (3,187 m). 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

4488-521: The ICS timescale, the Pleistocene is divided into four stages or ages , the Gelasian , Calabrian , Chibanian (previously the unofficial "Middle Pleistocene"), and Upper Pleistocene (unofficially the "Tarantian"). In addition to these international subdivisions, various regional subdivisions are often used. In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for

4620-631: The Isthmus of Panama , causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia . The end of the Early Pleistocene is marked by

4752-563: The Lassen Volcanic National Park on August 9, 1916. The park, 106,372 acres (430.47 km ) in area, can be reached from the California State Route 89 highway. Between 385,000 and 315,000 years ago, volcanism at the Lassen center shifted from andesitic stratovolcano construction to production of dacite domes. Over the past 300,000 years, the Lassen Peak area has produced more than 30 lava domes, Lassen Peak being

4884-660: The Laurentide Ice Sheet . Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch , which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ('most new' or 'newest') from the Greek πλεῖστος ( pleīstos ) 'most' and καινός ( kainós ( Latinized as cænus ) 'new'). This contrasts with

5016-593: The Mid-Pleistocene Transition , with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans also spread to the Australian continent and the Americas for the first time, co-incident with

5148-529: The Pit River . Simultaneously, dacite lava with lower viscosity than dacite from the previous eruption filled the summit crater, overflowing and extending in two streams for 1,000 ft (300 m) down the mountain's western and northeastern sides. On May 22, 1915, at about 4:00 p.m., Lassen Peak produced a violent explosive eruption that ejected rock and pumice and formed a larger and deeper crater at its summit. Within 30 minutes, volcanic ash and gas formed

5280-635: The Ruwenzori Range in east and central Africa were larger. Glaciers existed in the mountains of Ethiopia and to the west in the Atlas Mountains . In the northern hemisphere, many glaciers fused into one. The Cordilleran Ice Sheet covered the North American northwest; the east was covered by the Laurentide . The Fenno-Scandian ice sheet rested on northern Europe , including much of Great Britain;

5412-502: The United States Geological Survey . In addition to the fact that cinder cones usually erupt lava from base vents, there is a lack of physical evidence suggesting activity at the volcano since its formation in 1650. In addition, an old willow bush growing near the summit crater that was documented during the 1850s was still present in the 1880s after the alleged eruptions, suggesting that no eruptions took place during

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5544-477: The last glacial period ended about 10,000 years ago. Over 11 major glacial events have been identified, as well as many minor glacial events. A major glacial event is a general glacial excursion, termed a "glacial." Glacials are separated by "interglacials". During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials". These events are defined differently in different regions of

5676-588: The woolly rhinoceros , various giraffids , such as the Sivatherium ; ground sloths , Irish elk , cave lions , cave bears , Gomphotheres , American lions , dire wolves , and short-faced bears , began late in the Pleistocene and continued into the Holocene. Neanderthals also became extinct during this period. At the end of the last ice age, cold-blooded animals, smaller mammals like wood mice , migratory birds, and swifter animals like whitetail deer had replaced

5808-511: The 1850s. The areas surrounding Lassen Peak, especially to its east, south, and southeast, represented a meeting ground for Maidu , Yana , Yahi , and Atsugewi Native Americans . The volcano is known among some native populations as Amblu Kai , which means "Mountain Ripped Apart" or "Fire Mountain," and as Kom Yamani, which means "Snow Mountain," among the Mountain Maidu . Because

5940-416: The 1950s, but have grown weaker over time; they can still be found among the volcano's summit craters. These hydrothermal features are monitored continuously for their physical and chemical conditions by the United States Geological Survey. Climbers reported steam eruptions in the summit craters for decades after activity apparently ceased in 1921, and the naturalist Paul Schulz documented 30 steam vents at

6072-525: The 1980 eruption of Mount St. Helens. Lassen Peak Lassen Peak ( / ˈ l æ s ə n / LASS -ən ), commonly referred to as Mount Lassen , is a 10,457 ft (3,187 m) 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

6204-601: 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,

6336-608: 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 (stratovolcano). Following the end of volcanism at Brokeoff Volcano hydrothermal fluids began chemically weathering minerals in

6468-679: The Cascades, behind 14,179 ft (4,322 m) Mount Shasta , which lies 80 mi (130 km) 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. Lassen Peak has the highest known winter snowfall amounts in California, with an average annual snowfall of 660 in (1,676 cm); in some years, more than 1,000 in (2,500 cm) of snow falls at its base elevation of 8,250 ft (2,515 m) at Lake Helen . The Lassen Peak area receives more precipitation (rain, sleet, hail, snow, etc.) than anywhere in

6600-558: The Early Pleistocene Gelasian . Early Pleistocene stages were shallow and frequent. The latest were the most intense and most widely spaced. By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number and interglacials receive an odd number. The first major glacial was MIS2-4 at about 85–11 ka BP. The largest glacials were 2, 6, 12, and 16. The warmest interglacials were 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under

6732-409: The Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors. The Mid-Pleistocene Transition , approximately one million years ago, saw

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6864-585: The Fantastic Lava Beds . It also created the rockfalls at Chaos Jumbles. The only active Cascade volcano with an elevation above 10,000 ft (3,000 m) 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 2,000 ft (610 m) above its surroundings, and an approximate volume of 0.60 cu mi (2.5 km ). Unlike more conventional, conical stratovolcanoes like Mount Shasta or Mount Rainier, Lassen Peak

6996-482: The Lassen Peak National Monument in 1907. Despite Native population claims that Lassen Peak was "full of fire and water" and would erupt again, this motion was based on the general belief that Lassen Peak was now extinct , and that its vicinity contained intriguing volcanic phenomena, which could be studied and observed. Once the volcano became active again in 1914, the monument was expanded to establish

7128-634: 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 like mammals, reptiles , amphibians , fish, and birds, including bald eagles , which are listed as "Threatened" under

7260-756: The Lassen Peak volcanic center, with features located southeast and southwest of Lassen Peak, represents the largest geothermal area in the United States besides the one present at Yellowstone National Park. The Chaos Crags, a series of five small lava domes, represent the youngest part of Lassen volcanic center's dome field, reaching an elevation of about 1,800 ft (550 m) above their surroundings. They were produced by vigorous explosive eruptions of pumice and ash followed by effusive activity, which created unstable edifices that partially collapsed and formed pyroclastic flows made of incandescent lava blocks and lithic ash. Six domes were originally formed, though one

7392-688: The Morgan and Growler Hot Springs south of the national park in Mill Canyon. These are produced by the boiling of underground bodies of water, which generates steam. At Bumpass Hell, these features are at their most vigorous, with temperatures reaching 322 °F (161 °C) at Big Boiler, the park's biggest fumarole and one of the hottest hydrothermal fumaroles in the world. Because of their acidic conditions and heat, none of these hydrothermal bodies are safe for bathing except for at Drakesbad Guest Ranch. Fumaroles near Lassen Peak in particular remained active through

7524-468: The National Park Service if an eruption were imminent. Although basaltic lava flows are the most common eruptive activity in the Lassen volcanic center, they could also produce more violent and thus more hazardous silicic lava flows, in addition to building additional, unstable lava domes that could collapse and spawn pyroclastic flows that could extend for several miles. Because Lassen Peak has

7656-754: The National Park Service. His photographs have been used to help understand the timeline and geology of the 1915 eruptions of Lassen Peak. One of Lassen Peak's 1917 eruptions was captured on film by Justin Hammer from the nearby Catfish Lake. Originally silent, the film features sound effects added by his grandson, Craig Martin. The film was rediscovered and published in 2015 by the Shasta Historical Society . Lassen Peak remains an active volcano , as volcanic activity including fumaroles (steam vents), hot springs , and mudpots can be found throughout Lassen Volcanic National Park. Their activity varies based on

7788-479: The North American west. Lake Bonneville , for example, stood where Great Salt Lake now does. In Eurasia, large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided . African lakes were fuller, apparently from decreased evaporation. Deserts, on the other hand, were drier and more extensive. Rainfall was lower because of the decreases in oceanic and other evaporation. It has been estimated that during

7920-434: The Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. Radiocarbon dating is considered to be inaccurate beyond around 50,000 years ago. Marine isotope stages (MIS) derived from Oxygen isotopes are often used for giving approximate dates. Pleistocene non-marine sediments are found primarily in fluvial deposits , lakebeds, slope and loess deposits as well as in

8052-490: The Pleistocene's overall climate could be characterised as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru , warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places. It

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8184-494: The Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP . The start date has now been rounded down to 2.580 million years BP. The IUGS has yet to approve a type section , Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary ( i.e.

8316-782: The Pleistocene, the East Antarctic Ice Sheet thinned by at least 500 meters, and that thinning since the Last Glacial Maximum is less than 50 meters and probably started after ca 14 ka. During the 2.5 million years of the Pleistocene, numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of

8448-411: The Pleistocene, the plates upon which they sit probably having moved no more than 100 km (62 mi) relative to each other since the beginning of the period. In glacial periods, the sea level would drop by up to 120 m (390 ft) lower than today during peak glaciation, exposing large areas of the present continental shelf as dry land. According to Mark Lynas (through collected data),

8580-551: 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

8712-483: 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

8844-687: The appearance of Homo sapiens about 300,000 years ago. Artifacts associated with modern human behavior are unambiguously attested starting 40,000–50,000 years ago. According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciation in the Middle Palaeolithic during the Eemian Stage , spreading all over the ice-free world during the late Pleistocene. A 2005 study posits that humans in this migration interbred with archaic human forms already outside of Africa by

8976-470: The area was not suitable for permanent habitation, there is relatively scarce archaeological evidence of a native presence in the Lassen area. The first white man to reach Lassen Peak was Jedediah Smith , who passed through the area in 1821 as he made his way for the western coast of the United States. After the California Gold Rush brought increased numbers of settlers into the area, Lassen Peak

9108-515: The articles for those names. Both marine and continental faunas were essentially modern but with many more large land mammals such as Mammoths , Mastodons , Diprotodons , Smilodons , tigers , lions , Aurochs , short-faced bears , giant sloths , species within Gigantopithecus and others. Isolated landmasses such as Australia , Madagascar , New Zealand and islands in the Pacific saw

9240-906: The bottoms of valleys along streams and lakes support Pacific tree frogs , Western terrestrial garter snakes , common snipes , and mountain pocket gophers . Other animals found within the national park area include snakes like 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. Lassen Peak lies near

9372-450: 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 12 cu mi (50 km) of material and created

9504-641: 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 1,200,000 acres (4,900 km ). Nearby towns include Mineral in Tehama County and Viola in Shasta County. Lassen Peak reaches an elevation of 10,440 ft (3,180 m), according to 1992 data from the U.S. National Geodetic Survey ; 1981 data from

9636-553: The construction of the Chaos Crag dome complex between 1100 and 1000 years ago and eruptions at Lassen Peak beginning in 1914. Prior to 1914, Lassen Peak likely underwent at least one explosive eruption, which created a summit crater 360 ft (110 m) deep with a diameter of 1,000 ft (300 m). Deposits from older mudflows that can be traced specifically to the Lassen dome have also been found in Hat Creek, Lost Creek, and in

9768-400: The dome fell on the upper flanks of the mountain, which were covered in more than 30 ft (9.1 m) of snow. The lava mixed with snow and rock to form a lahar (volcanically induced mudslide , landslide , and debris flow ), 0.5 mi (0.80 km) in width, which coursed down the side of the volcano, traveling 4 mi (6.4 km) and reaching Hat Creek . After being deflected to

9900-497: 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 106,372 acres (430.47 km ), was created to preserve the areas affected by the eruption for future observation and study, to protect

10032-606: The entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania . The current decaying glaciers of Mount Kenya , Mount Kilimanjaro , and

10164-772: The evolution of large birds and even reptiles such as the Elephant bird , moa , Haast's eagle , Quinkana , Megalania and Meiolania . The severe climatic changes during the Ice Age had major impacts on the fauna and flora. With each advance of the ice, large areas of the continents became depopulated, and plants and animals retreating southwards in front of the advancing glacier faced tremendous stress. The most severe stress resulted from drastic climatic changes, reduced living space, and curtailed food supply. A major extinction event of large mammals ( megafauna ), which included mammoths , mastodons , saber-toothed cats , glyptodons ,

10296-444: The extinction of most large-bodied animals in these regions. The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by

10428-410: The first volcano to erupt in the United States during the 20th century. Unlike eruptions at Mount Baker, Mount Rainier , Mount St. Helens, or Mount Hood during the 19th century, Lassen Peak's eruptions were very well documented by newspapers and extensively photographed. Though there is a large supply of images documenting these eruptions at Lassen Peak, the best and most complete images were taken by

10560-486: The first woman to reach the summit of Lassen Peak, wanting to sketch the surrounding landscape. A tarn lake on Lassen Peak is named "Lake Helen" in her honor. The Bumpass Hell, a hydrothermal vent area near Lassen Peak, was named after a pioneer who suffered burns there and lost his leg shortly after. Other historic names for Lassen Peak include Mount Joseph (from 1827), Snow Butte, Sister Buttes, and Mount Lassen. United States President Theodore Roosevelt established

10692-478: The formation of Brokeoff, other, smaller volcanoes began to form. Shield volcanoes like Raker Peak, Red Mountain, Prospect Peak, and Mount Harkness appeared. At this point, the Pleistocene was coming to an end. One additional and final vent formed on the northeastern flank of the volcano, erupting glassy dacitic flows. Over time, the volcano became dilapidated from extensive erosion and hydrothermal alteration, and

10824-416: 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 280 mi (450 km) to

10956-414: The glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondence between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another. For most of the 20th century, only

11088-623: The ground still capable of eruptions. Thus it poses a threat to the nearby area through lava flows , pyroclastic flows , lahars (volcanically induced mudslides , landslides , and debris flows ), ash, avalanches , and floods. To monitor this threat, Lassen Peak and the surrounding vicinity are closely observed with sensors by the California Volcano Observatory . Lassen Peak lies within Lassen Volcanic National Park , in Shasta County , California, 55 mi (89 km) east of

11220-450: The historical terminology was established. Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use (Latin: pluvia , rain). A pluvial is a warmer period of increased rainfall; an interpluvial is of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread. There

11352-480: The hydrothermally altered rocks near the central vent, creating the deep Mill Canyon and exposing deep into the core of the ancient volcano. Many of the lava flows along the flanks of Brokeoff Volcano were not as extensively chemically weathered, resulting in the flanks of much of the volcano being preserved. Remnants of the flanks of Brokeoff Volcano include Brokeoff Mountain, Mount Conard, Pilot Pinnacle, Mount Diller, and Diamond Peak. The area near Lassen Peak became

11484-445: The immediately preceding Pliocene ("newer", from πλείων ( pleíōn , "more") and kainós ) and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος ( hólos , "whole") and kainós ) epoch , which extends to the present time. The Pleistocene has been dated from 2.580 million (±0.005) to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of

11616-613: The large amounts of material moved about by glaciers. Less common are cave deposits, travertines and volcanic deposits (lavas, ashes). Pleistocene marine deposits are found primarily in shallow marine basins mostly (but with important exceptions) in areas within a few tens of kilometres of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred metres. The modern continents were essentially at their present positions during

11748-412: The largest. These lava domes formed as a result of rising lava that was pushed up but was too viscous to escape its source, creating steep edifices. Lassen Peak's lava dome formed 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. No volcanic activity took place 190,000 years ago to roughly 90,000 years ago, but during

11880-525: The last 100,000 years, there have been at least 12 periods of eruptive activity in the Lassen volcanic center, and since 90,000 years ago, the Twin Lakes sequence has been producing mixed lavas with variable appearances and compositions, including andesite and basaltic andesite lava flows and agglutinated volcanic cones (made of fused pyroclastic rocks) located by the Lassen dome field. The Twin Lakes sequence includes

12012-581: 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

12144-526: The latest period of repeated glaciation , up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9700 BCE (11,700 calendar years BP). The end of the Younger Dryas is the official start of the current Holocene Epoch . Although it is considered an epoch, the Holocene is not significantly different from previous interglacial intervals within the Pleistocene. In

12276-448: 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

12408-519: The local businessman Benjamin Franklin Loomis . Using an 8x10-inch camera with glass-plate negatives, Loomis made his own film and set up a darkroom in a tent. He wrote of the eruption he witnessed on June 14, 1914, "The sight was fearfully grand." Loomis's pictures were published in his book Pictorial History of the Lassen Volcano (1926); a number of his original plates remain in the archives of

12540-466: The lower Palaeolithic they disappeared, and the only hominin species found in fossilic records is Homo erectus for much of the Pleistocene. Acheulean lithics appear along with Homo erectus , some 1.8 million years ago, replacing the more primitive Oldowan industry used by A. garhi and by the earliest species of Homo . The Middle Paleolithic saw more varied speciation within Homo , including

12672-478: The megafauna and migrated north. Late Pleistocene bighorn sheep were more slender and had longer legs than their descendants today. Scientists believe that the change in predator fauna after the late Pleistocene extinctions resulted in a change of body shape as the species adapted for increased power rather than speed. The extinctions hardly affected Africa but were especially severe in North America where native horses and camels were wiped out. In July 2018,

12804-456: The mountain during summer. The mountain trail lasts between four and six hours, spans 7.4 mi (12 km), 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

12936-523: The mountain would blow itself to pieces". In May 1914, almost exactly seven years later, the volcano began a large explosive eruption sequence. More than a hundred eruptions of varying size took place over the next seven years, attracting national interest and the designation of national park in 1916. The state of California is located on the Pacific Ring of Fire , an area of highly active tectonic activity that includes seismicity and volcanism. Brokeoff and

13068-422: 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

13200-519: The north. The southern entrance to the park area has a winter sports area where visitors can ski , snowshoe , and within the Lassen National Forest, visitors can also bicycle, go boating , or use snowmobiles . Pleistocene The Pleistocene ( / ˈ p l aɪ s t ə ˌ s iː n , - s t oʊ -/ PLY -stə-seen, -⁠stoh- ; referred to colloquially as the Ice Age )

13332-493: The northeast of Brokeoff Volcano, with volcanism currently focused around the modern Lassen Peak . Following the end of volcanism at Brokeoff Volcano, cooling magma beneath the surface continued to drive hot, highly reactive hydrothermal fluids circulating near the central vent of the volcano. These hydrothermal fluids chemically weathered the volcanic rocks near the central vent, making them particularly susceptible to physical erosion. Glaciers and streams were able to rapidly erode

13464-541: The northern crater on Lassen Peak's summit, with eruptions lasting two days and producing an ash cloud that extended 10,000 to 12,000 ft (3,000 to 3,700 m) into the sky. Another 21 explosions occurred in June, further transforming the crater and creating a new vent on Lassen Peak's northwestern summit. More steam eruptions followed in June 1919 and similar activity was observed the next year, on April 8–9, 1920, followed by more steam eruptions lasting 10–12 hours in October of

13596-523: The northwest at Emigrant Pass, the lahar extended an additional 7 mi (11 km) down Lost Creek. On May 20, the lower Hat Creek valley flooded with muddy water, which damaged ranch houses in the Old Station area and caused minor injuries among a few people, all of whom escaped. Removing homes from their foundation, the lahar also uprooted trees more than 100 ft (30 m) tall. The flood continued for another 30 mi (48 km), killing fish in

13728-484: The other volcanoes near Lassen Peak were produced by subduction of the oceanic Juan de Fuca Plate under the North American Plate . 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

13860-441: The park with tiltmeters , seismometers , and inclinometers . Prior to 1996, geodetic surveys at Lassen Peak did not detect ground deformation, but Interferometric synthetic-aperture radar (InSAR) surveys between 1996 and 2000 suggested that downward subsidence was occurring at a rate of 0.39 in (10 mm) each year within a circular area with a diameter of 25 mi (40 km) centered just 3.1 mi (5 km) of

13992-474: The past 825,000 years, the area has produced hundreds of explosive eruptions over an area of 200 sq mi (520 km ), 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 (alternatively known as Mount Tehama). Around

14124-487: The peak's inherent instability. The volcano is monitored by the California Volcano Observatory, which has a sensor network that can measure increased seismicity, ground deformation, or gas emissions suggesting movement of magma towards the surface near the volcano. The United States Geological Survey, in cooperation with the National Park Service, has been monitoring Lassen Peak and other volcanic areas in

14256-472: The period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology . The name is a combination of Ancient Greek πλεῖστος ( pleîstos ) 'most' and καινός ( kainós ; Latinized as cænus ) 'new'. At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by

14388-417: The ratio of O to O (two isotopes of oxygen ) by mass (measured by a mass spectrometer ) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in O , which is included in the tests of the microorganisms ( foraminifera ) contributing the calcite. A more recent version of

14520-455: The recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age. Formerly, the boundary between the two epochs was drawn at the time when the foraminiferal species Hyalinea baltica first appeared in the marine section at La Castella, Calabria, Italy. However, the revised definition of the Quaternary , by pushing back the start date of

14652-613: 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 (such as Mount Maidu ) formed in the vicinity of Lassen Volcanic National Park, building volcanic cones before going extinct and undergoing erosion. For most volcanic centers in

14784-478: The same border, indicating that the Cascade Arc's southern end migrates at a rate of 0.4 to 1 in (1.0 to 2.5 cm) 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 (silica-rich) rhyolite . The Lassen volcanic center is fed by two magma chambers, one calc-alkaline reservoir common to

14916-606: The same time, about 614,000 years ago, an explosive eruption southwest of Lassen Peak produced 20 cu mi (83 km ) 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

15048-461: The same year. During February 1921, white steam erupted from eastern fissures on the volcano. In total, about 400 eruptions were observed between 1914 and 1921, which were the last eruptions in the Cascades before the 1980 eruption of Mount St. Helens, which was the only other volcanic eruption in the contiguous United States during the 20th century. During its eruptions in the early 20th century, Lassen Peak attracted widespread media attention as

15180-407: The sampling process makes use of modern glacial ice cores. Although less rich in O than seawater, the snow that fell on the glacier year by year nevertheless contained O and O in a ratio that depended on the mean annual temperature. Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of

15312-445: The season; during the spring, when meltwater is more abundant, fumaroles and pools of water have lower temperatures, while mudpots have more fluid mud supplies. During summer and droughts, they become drier and hotter, since they cannot be cooled by ground water. Geothermal activity can be observed at Bumpass Hell, Little Hot Springs Valley, Pilot Pinnacle, Sulphur Works, Devils Kitchen, Boiling Springs Lake, and Terminal Geyser, as well as

15444-632: The sole factor responsible for the variations in climate since they explain neither the long-term cooling trend over the Plio-Pleistocene nor the millennial variations in the Greenland Ice Cores known as Dansgaard-Oeschger events and Heinrich events. Milankovitch pacing seems to best explain glaciation events with periodicity of 100,000, 40,000, and 20,000 years. Such a pattern seems to fit the information on climate change found in oxygen isotope cores. In oxygen isotope ratio analysis, variations in

15576-511: 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

15708-421: The study of cyclical climate changes. The glacials in the following tables show historical usages, are a simplification of a much more complex cycle of variation in climate and terrain, and are generally no longer used. These names have been abandoned in favour of numeric data because many of the correlations were found to be either inexact or incorrect and more than four major glacials have been recognised since

15840-403: The summit in the 1950s. A report from the United States Geological Survey declared that "No one can say when, but it is almost certain that the Lassen area will experience volcanic eruptions again." Similarly, the California Volcano Observatory lists its threat level as "Very High." At the time of the early 20th century eruptions, the area surrounding the volcano was only sparsely populated, but

15972-494: The threat of an avalanche from nearby Chaos Crag if volcanic activity renewed in the area or an earthquake occurred, the Visitor Center for Lassen Peak located at Manzanita Lake closed in 1974. In 1993, a rockfall with a volume of 13,000 cu yd (9,900 m ) fell down Lassen Peak's northeastern flank, but no visitors were harmed. Despite the volcano's current quiet state, rockfalls still pose significant hazards due to

16104-622: The upper boundary). The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W. The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone , isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils : Discoaster pentaradiatus and Discoaster surculus . The Pleistocene covers

16236-406: The vents built by this activity is Lassen Peak. 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. Eagles and hawks can be frequently noted on high crags, and squirrels and pika live about the mountain. Hiking is especially popular on

16368-441: The volcano, as well a layer of pumice and volcanic ash that reached as far as 25 mi (40 km) northeast; volcanic ash was detected up to 280 mi (450 km) east at the city of Elko, Nevada . Additionally, the lava flow on the volcano's northeastern flank was removed by this eruption, but not the similar deposit on the western flank. The eruptive output volume totaled 0.007 cu mi (0.029 km ), dwarfed by

16500-501: The volcano. As a result, additional surveys using the Global Positioning System took place in 2004, and further InSAR surveys showed that subsidence continued through 2010. Lassen Peak is one of four Cascade volcanoes that has undergone subsidence since 1990, with Medicine Lake Volcano , Mount Baker, and Mount St. Helens. Though not conclusively linked to a possible eruption, this subsidence may offer insight into how magma

16632-533: 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 19 mi (30 km) to the south of Lassen Peak, but currently the southern edge of the Lassen Volcanic National Park now marks

16764-543: Was a series of glacials and interglacials, stadials and interstadials, mirroring periodic climate changes. The main factor at work in climate cycling is now believed to be Milankovitch cycles . These are periodic variations in regional and planetary solar radiation reaching the Earth caused by several repeating changes in the Earth's motion. The effects of Milankovitch cycles were enhanced by various positive feedbacks related to increases in atmospheric carbon dioxide concentrations and Earth's albedo. Milankovitch cycles cannot be

16896-683: 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 11 mi (18 km) and 15 mi (24 km) wide and more than 11,000 ft (3,353 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 . Soon after

17028-464: Was declared a national monument by President Theodore Roosevelt to protect the area for "future generations to study and enjoy". 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

17160-478: Was destroyed by a pyroclastic flow. Roughly 350 years ago, one of the domes collapsed to produce the Chaos Jumbles, an area where three enormous rockfalls transformed the local area and traveled as far as 4 mi (6.4 km) down the dome's slopes. Cinder Cone, which reaches an elevation of 700 ft (210 m) above its surrounding area in the northeastern region of the Lassen Volcanic National Park, forms

17292-466: Was eroded by creeks and glaciers. Later activity built more than thirty other cones known as the Lassen Domes . Today the most active volcano in the area is Lassen Peak . Other smaller craters younger than 50,000 years are also active. 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

17424-459: Was named in honor of a Danish blacksmith, Peter Lassen , who guided immigrants past the peak to the Sacramento Valley during the 1830s. This trail was replaced by the Nobles Emigrant Trail , named for the guide William Nobles, who pioneered the trail in 1851. Lassen Peak's first recorded ascent took place in 1851, led by Grover K. Godfrey. In 1864, painter Helen Tanner Brodt became

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