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Geology Of The Lassen Volcanic Area
The Lassen volcanic area presents a geological record of sedimentation and volcanic activity in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat and molten rock from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years, including these in the Lassen volcanic areas. Between 3 and 4 million years ago, volcanic-derived mud flows called lahars streamed down several major mountains that included nearby but now extinct Mount Yana and Mount Maidu to become the Tuscan Formation. Basaltic and later andesitic to dacitic flows of lava covered increasingly larger areas of this formation to eventually form t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eruptions In The Lassen Area In The Last 50,000 Years-map
Several types of volcanic eruptions—during which lava, tephra ( ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three different types of eruptions: * Magmatic eruptions are the most well-observed type of eruption. They involve the decompression of gas within magma that propels it forward. * Phreatic eruptions are driven by the superheating of steam due to the close proximity of magma. This type exhibits no magmatic release, instead causing the granulation of existing rock. * Phreatomagmatic eruptions are driven by the direct interaction of magma and water, as opposed to phreatic er ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic. Along with basalts, andesites are a component of the Martian crust. The name ''andesite'' is derived from the Andes mountain range, where this rock type is found in abundance. It was first applied by Christian Leopold von Buch in 1826. Description Andesite is an aphanitic (fine-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cinder Cone And The Fantastic Lava Beds
Cinder Cone is a cinder cone volcano in Lassen Volcanic National Park within the United States. It is located about northeast of Lassen Peak and provides an excellent view of Brokeoff Mountain, Lassen Peak, and Chaos Crags. The cone was built to a height of above the surrounding area and spread ash over . Then, like many cinder cones, it was snuffed out when several basalt lava flows erupted from its base. These flows, called the Fantastic Lava Beds, spread northeast and southwest, and dammed creeks, first creating Snag Lake on the south and then Butte Lake to the north. Butte Lake is fed by water from Snag Lake seeping through the lava beds. Nobles Emigrant Trail goes around Snag Lake and follows the edge of the lava beds. Its age has been controversial since the 1870s, when many people thought it was only a few decades old. Later, the cone and associated lava flows were thought to have formed about 1700 or during a 300-year- long series of eruptions ending in 1851. Rece ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cinder Cone
A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is symmetrical; with slopes between 30 and 40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit. Mechanics of eruption Cinder cones range in size from tens to hundreds of meters tall and often have a bowl-shaped crater at the summit. They are composed of loose pyroclastic material ( cinder or scoria), which distinguishes them from ''spatter cones'', which are composed of agglomerated volcanic bombs. The pyroclastic material making up a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phreatic
''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" or "spring") is used in hydrology and the earth sciences to refer to matters relating to ground water (an aquifer) below the water table. The term 'phreatic surface' indicates the location where the pore water pressure is under atmospheric conditions (i.e. the pressure head is zero). This surface normally coincides with the water table. The slope of the phreatic surface is assumed to indicate the direction of ground water movement in an unconfined aquifer. The phreatic zone, below the phreatic surface where rock and soil is saturated with water, is the counterpart of the vadose zone, or unsaturated zone, above. Unconfined aquifers are also referred to as phreatic aquifers because their upper boundary is provided by the phreatic surfac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chaos Crags
Chaos Crags is the youngest group of lava domes in Lassen Volcanic National Park, California. They formed as six dacite domes 1,100-1,000 years ago, one dome collapsing during an explosive eruption about 70 years later. The eruptions at the Chaos Crags mark one of just three instances of Holocene activity within the Lassen volcanic center. The cluster of domes is located north of Lassen Peak and form part of the southernmost segment of the Cascade Range in Northern California. Each year, a lake forms at the base of the Crags, and typically dries by the end of the summer season. From the base of the crags and extending toward the northwest corner of the park is Chaos Jumbles, a rock avalanche that undermined Chaos Crags' northwest slope 300 years ago. Riding on a cushion of compressed air (see sturzstrom), the rock debris traveled at about , flattened the forest before it, and dammed Manzanita Creek, forming Manzanita Lake. In addition to the possibility of forming additio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wisconsin Glaciation
The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the Pinedale glaciation. The Wisconsin glaciation extended from approximately 75,000 to 11,000 years ago, between the Sangamonian Stage and the current interglacial, the Holocene. The maximum ice extent occurred approximately 25,000–21,000 years ago during the last glacial maximum, also known as the ''Late Wisconsin'' in North America. This glaciation radically altered the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glacial Erosion
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, transports it to another location where it is deposit (geology), deposited. Erosion is distinct from weathering which involves no movement. Removal of rock or soil as clastic sediment is referred to as ''physical'' or ''mechanical'' erosion; this contrasts with ''chemical'' erosion, where soil or rock material is removed from an area by Solvation, dissolution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres. Agents of erosion include rainfall; bedrock wear in rivers; coastal erosion by the sea and Wind wave, waves; glacier, glacial Plucking (glaciation), plucking, Abrasion (geology), abrasion, and scour; areal flooding; Aeolian processes, wind abrasion; groundwater processes; and Mass wasti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lassen Peak
Lassen Peak ( ), commonly referred to as Mount Lassen, is a lava dome volcano and the southernmost active volcano in the Cascade Range of the Western United States. Located in the Shasta Cascade region of Northern California, it is part of the Cascade Volcanic Arc, which stretches from southwestern British Columbia to northern California. Lassen Peak reaches an elevation of , standing above the northern Sacramento Valley. It supports many flora and fauna among its diverse habitats, which are subject to frequent snowfall and reach high elevations. 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 nea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lava Dome
In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on Earth are lava dome forming. The geochemistry of lava domes can vary from basalt (e.g. Semeru, 1946) to rhyolite (e.g. Chaiten, 2010) although the majority are of intermediate composition (such as Santiaguito, dacite-andesite, present day) The characteristic dome shape is attributed to high viscosity that prevents the lava from flowing very far. This high viscosity can be obtained in two ways: by high levels of silica in the magma, or by degassing of fluid magma. Since viscous basaltic and andesitic domes weather fast and easily break apart by further input of fluid lava, most of the preserved domes have high silica content and consist of rhyolite or dacite. Existence of lava domes has been suggested for some domed structures on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stratovolcano
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as . Stratovolcanoes are sometimes called composite volcanoes because of their composite stratified structure, built up from sequential outpourings of erupted materials. They are among the most common types of volcanoes, in contrast to the less common shield volcano ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mount Tehama
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, the Central Valley of California, and many of the park's other features. On clear days, Mount Shasta can also be seen in the distance. Brokeoff Volcano was active from 590,000 to 38 I7,000 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 and had a basal circumference of approxim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
