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Encyclopedia > Mount Mazama
Mount Mazama

Most of Mazama fell into a large caldera, which was later filled with Crater Lake
Elevation 8,159 feet (2,487 metres)
Location Oregon, USA
Range Cascade Volcanic Arc, Cascade Range
Coordinates 42°54′59″N, 122°05′04″W
Topo map USGS Crater Lake East 42122-H1
Type Caldera
Last eruption 2290 BC ± 300 years
Easiest route drive

Mount Mazama is a destroyed stratovolcano in the Oregon part of the Cascade Volcanic Belt and the Cascade Range. The volcano's collapsed caldera holds Crater Lake, and the entire mountain is located in Crater Lake National Park. Image File history File linksMetadata Download high resolution version (2560x1920, 471 KB) Summary Crater lake from above Taken by Samion Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... A topographical summit is a point on a surface which is higher in elevation than all points immediately adjacent to it. ... Official language(s) None Capital Salem Largest city Portland Area  Ranked 9th  - Total 98,466 sq mi (255,026 km²)  - Width 260 miles (420 km)  - Length 360 miles (580 km)  - % water 2. ... The Himalaya as seen from the International Space Station A mountain range is a group of mountains bordered by lowlands or separated from other mountain ranges by passes or rivers. ... This article or section does not adequately cite its references or sources. ... Mount Adams in Washington The Cascade Range is a mountainous region famous for its chain of tall volcanoes called the High Cascades that run north-south along the west coast of North America from British Columbia through Washington and Oregon to the Shasta Cascade area of northern California. ... Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; large version (pdf, 1. ... Example of a topographic map with contour lines Part of the same map in a perspective shaded relief view illustrates how the contour lines of the original follow the terrain Topographic maps are a variety of map characterized by large-scale detail and quantitative representation of relief, usually using contour... The United States Geological Survey (USGS) is a scientific agency of the United States government. ... Mountains can be characterized in several ways. ... Satellite image of Santorini. ... For other uses, see Volcano (disambiguation). ... Southern and northern Mount Everest climbing routes as seen from the International Space Station. ... Stratovolcano Mount St. ... Official language(s) None Capital Salem Largest city Portland Area  Ranked 9th  - Total 98,466 sq mi (255,026 km²)  - Width 260 miles (420 km)  - Length 360 miles (580 km)  - % water 2. ... This article or section does not cite its references or sources. ... Mount Adams in Washington The Cascade Range is a mountainous region famous for its chain of tall volcanoes called the High Cascades that run north-south along the west coast of North America from British Columbia through Washington and Oregon to the Shasta Cascade area of northern California. ... For other uses, see Volcano (disambiguation). ... Satellite image of Santorini. ... Crater Lake is a caldera lake in the U.S. state of Oregon. ... Lyskamm, 4 527 m, Pennine Alps A mountain is a landform that extends above the surrounding terrain in a limited area. ... Crater Lake National Park is the U.S.s fifth oldest[1] National Park whose most famous feature is Crater Lake. ...


Mazama is most famous for a catastrophic volcanic eruption that occurred around 5,677 (± 150) BC[1]. The eruption, estimated to have been 42 times more powerful than Mt. St. Helens' 1980 blast, reduced Mazama's approximate 11,000 foot (c.3,350 m) height by around half a mile (about 1 km) when much of the volcano fell into the volcano's partially emptied neck and magma chamber. At 8,159 feet (2,487 m), Hillman Peak is now the highest point on the rim. This article is about volcanoes in geology. ... A magma chamber is a chamber typically between 1 km and 10 km beneath the surface of the Earth formed as rising magma forms a reservoir if it is unable to rise any further. ...

Contents

History

The Klamath Native Americans of the area thought that the mountain was inhabited by Llao, their god of the underworld. After the mountain destroyed itself the Klamaths recounted the events as a great battle between Lloa and his rival Skell, their sky god. This article is in need of attention from an expert on the subject. ... This article discusses the term God in the context of monotheism and henotheism. ... // In the study of mythology and religion, the underworld is a generic term approximately equivalent to the lay term afterlife, referring to any place to which newly dead souls go. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ...


Much of what we know of Mazama's geology comes from a study by Howel Williams of the University of California, Berkeley and later, from USGS geologist Charles R. Bacon who expanded and modified Williams' work. Howel Williams (1898-1980) was a noted American geologist and volcanologist. ... Sather tower (the Campanile) looking out over the San Francisco Bay and Mount Tamalpais. ... The United States Geological Survey (USGS) is a scientific agency of the United States government. ...


Geology

For a summary see: Crater Lake National Park#Geology Crater Lake National Park is the U.S.s fifth oldest[1] National Park whose most famous feature is Crater Lake. ...


Growth phase

Mazama started to grow around 400,000 years ago in the Pleistocene, mainly from lava flows interbeded with some pyroclastic material. These early flows averaged 20 to 30 feet (6 to 9 m) thick and appear to have been emplaced over a few years to a few centuries. Several shield volcanoes were created by these flows and numerous cinder cones grew in the immediate area (these may or may not be parasitic vents). More explosive eruptions started around 75,000 years ago and built a westward-trending line of composite cones. The Pleistocene epoch (IPA: ) is part of the geologic timescale. ... Pyroclastic rocks are formed from lavas which are ejected into the air, as occur in pyroclastic flows or Plinian eruptions. ... Shield volcano A shield volcano is a large volcano with shallowly-sloping sides. ... Puʻu ʻŌʻō, a cinder-and-spatter cone on Kīlauea, Hawaiʻi Volcanic cones are among the simplest volcano formations in the world. ... Stratovolcano Mount St. ...


Cone building eruptions lasted until around 50,000 years ago when andesite lava flowed down Mazama's north and southwest slopes. Relatively few of the cone building eruptions issued from the same vent, resulting in a highly complex approximately 11,000 foot (c.3,350 m) structure made of overlapping composite cones and shield volcanoes. Consequently, Mazama's base was broader and its side not as steep as today's Mount Shasta or Mount Rainier. Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Mount Shasta, a 14,179-foot (4,322 m)[1] stratovolcano, is the second-highest peak in the Cascade Range and the fifth highest peak in California. ... Mount Rainier is a stratovolcano in Pierce County, Washington, located 54 miles (87 km) southeast of Seattle, Washington, in the United States. ...


Silica enrichment

After its cone building phase, Mazama lavas became increasingly silica-rich and viscous - two conditions that tend to trap explosive gases. The first major eruption in this new cycle of Mazama's life occurred about 10,000 years later, when dacite flows high on the volcano's southwest face formed a series of domes. These structures were subsequently destroyed by either collapse or steam explosions (see phreatic eruption). Either way, their destruction created large landslides that left deposits at the head of Munsen Valley and as far away as Devils Backbone. The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... This article or section does not adequately cite its references or sources. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ... It has been suggested that this article be split into articles entitled steam and water vapor, accessible from a disambiguation page. ... Phreatic eruption at the summit of Mount St. ... Rockslide redirects here. ...


Mazama's next major eruptive period occurred between 25,000 and 30,000 years ago and extruded rhyodacite lava (which has a higher silica content than dacite). These thick, slow moving, pasty flows erupted from a vent on Mazama's northeast flank and solidified to form 600 foot (180 m) high Redcloud Cliff (later cut in two by caldera subsidence) and a dome above what today is Steel Bay. BOOOOOOOOYAAAAAAAA!!!!!!!!!!! ... Satellite image of Santorini. ...


The volcano then went dormant for roughly the next 20,000 years, while successive ice age glaciers (probably as thick as 1,000 feet (300 m) in troughs) cut large valleys into the mountain's sides. One of the largest glaciers flowed down Munson Valley near the present location of park headquarters, down Annie Creek Valley, and perhaps as far as Fort Klamath. When the last ice age ended 12,000 years ago, those glaciers retreated upslope past the elevation of the current caldera's rim. While Mazama slept, its magma chamber was going through some differentiation, with lighter, more gas- and silica-rich rocks collecting closer to the surface. Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity and undergoes internal deformation. ... Fort Klamath was a military outpost near the western end of the Oregon Trail, between Crater Lake National Park and Upper Klamath Lake in Klamath County, Oregon, United States. ...


Explosive phase

Around 5000 BC Mazama awoke from its slumber with explosive rhyodacite eruptions on the northern part of the main summit where Llao Rock now resides. Great quantities of pumice and ash were ejected as a large crater was excavated by the explosions. The tephra was carried by prevailing winds to the east and southeast. Associated with this was a pyroclastic flow that was 1.25 miles (2 km) wide, 1,200 feet (about 360 m) thick at its deepest point, and contained 0.25 mi³ (1 km³) of material (later, caldera forming subsidence cut the partially filled crater in two, exposing it in cross section - today this is called Llao Rock). USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... (6th millennium BC – 5th millennium BC – 4th millennium BC – other millennia) Events 4713 BC – The epoch (origin) of the Julian Period described by Joseph Justus Scaliger occurred on January 1, the astronomical Julian day number zero. ... BOOOOOOOOYAAAAAAAA!!!!!!!!!!! ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Ash plume from Mt Cleveland, a stratovolcano Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash consists of very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ... Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ...


One to two hundred years later (based on radiocarbon dating) the last major eruption before the caldera was formed, the Cleetwood flow, occurred. This rhyodacite lava flow erupted from a vent near what is now the north caldera rim. The Cleetwood flow was still fluid when the caldera was formed, so it must have erupted just weeks to months beforehand. When Mazama later collapsed into itself, some of the Cleetwood lava backflowed into the caldera. Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 years[1]. Raw, i. ...


Mazama's final act started with a large eruption that sent a mile (1.6 km) wide column of hot tephra 5 to 10 miles (8 to 16 km) into the sky at almost twice the speed of sound. The column collapsed in a series of pyroclastic flows that covered much of the area between and downslope of Llao Rock and Redcloud Cliff. This flow, the first of many, was so hot that it solidified as a welded tuff called the Windglass Welded Tuff. Flow after flow followed in rapid succession, stressing the ability of Mazama's magma chamber to recharge. The mountain started to sag under its own weight. Concentric ring fractures started to form around the volcano, creating convenient conduits for additional volcanic vents. The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... A magma chamber is a chamber typically between 1 km and 10 km beneath the surface of the Earth formed as rising magma forms a reservoir if it is unable to rise any further. ...


The eruption entered its final and most destructive cycle with very large and erosive pyroclastic flows erupting from ring fractures all around the volcano. These flows moved out in all directions from Mazama, following river valleys and in some cases not coming to rest for 40 miles (65 km). As the eruptions were occurring Mazama was imploding. Río Peralonso - El Zulia (Norte de Santander), Colombia River Gambia flowing through Niokolokoba National Park Nevėžis River in Lithuania A river is a natural waterway usually formed by water derived from either precipitation or glacial meltwater, and flows from higher ground to lower ground. ...

The collapse and the erosive ring eruptions fed each other - the sinking volcano pushed magma upward and the erupting material both lubricated the downward subsidence and eroded the sides, making it easier for much of Mazama to sink into the earth. Also, the sudden and dramatic reduction in overpressure on the remaining gas charged molten rock in the magma chamber caused it to react by immediately exploding into a super-heated mix of liberated gases and various grades of pulverized and often frothy lava known as a pyroclastic flow. The force of the explosion pulverized previously solidified rock that happened to be nearby or that recently fell into the caldera from the collapse. USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ... The rocky side of a mountain creek near Orosí, Costa Rica. ...


Half of 70,000 year old Hillman Peak was blown away, exposing the cone in cross section. Many glacier-cut canyons were beheaded and now stand as notches in the caldera rim. Notable among these are Kerr Notch, Munson Valley, and Sun Notch.


The last pyroclastic flow of this stage was andestic scoria, indicating that Mazama was drawing on material deep from within its magma chamber. This layer of material now forms a dark band in ash layers associated with this eruption cycle (it also created the Pumice Desert). A last few dying gasps in the form of a series of relatively weak explosions then deposited a well-bedded layer of pumice lapilli and crystal-rich ash up to 50 feet (15 m) thick on the newly formed caldera rim. Scoria Scoria is the vesicular ejecta of mafic to intermediate magmas such as basalt and andesite. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Quartz crystal Copper(II) sulfate and iodine crystal Synthetic bismuth crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid...


In the end an estimated 11 to 14 mi³ (46 to 58 km³) of magma escaped from Mazama's magma chamber during this eruptive cycle as approximately 25 mi³ (104 km³) of tephra (magma is compact due to high pressure surrounding it). The magma was replaced by about the same volume of material when most of Mazama fell into its caldera.


Aftermath

Hundreds of square kilometres of the surrounding countryside were destroyed by material ejected from the collapse and associated eruptions. One pyroclastic flow traveled 40 miles (64 km) from Mazama down Rogue River Valley while another moved north in-between Mount Bailey and Mount Thielsen, moving over Diamond Lake (it finally came to rest in North Umpqua River valley). Winds carried tephra (ash and pumice) from Mazama northeast, where it covered over 500,000 square miles including nearly all of Oregon, Washington, northern California, Idaho, western Montana, and parts of Nevada, Wyoming, Alberta, British Columbia, and Saskatchewan. USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The Rogue Valley in southwestern Oregon The Rogue Valley is a farming and timber-producing region in southwestern Oregon in the United States. ... Mount Bailey is a relatively young tephra cone shield volcano in the Cascade Range that is located opposite Mount Thielsen from Diamond Lake in southern Oregon. ... Mount Thielsen is a stratovolcano in southern Oregon that has been so deeply eroded by glaciers that there is no summit crater and the upper part of the mountain is more or less a horn. ... Umpqua River with tributaries The North Umpqua River is a tributary of the Umpqua River, approximately 100 mi (161 km) long, in southwestern Oregon in the United States. ... A square mile is an English unit of area equal to that of a square with sides each 1 statute mile (≈1,609 m) in length. ... “Washington State” redirects here. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... This article or section does not adequately cite its references or sources. ... Official language(s) English Capital Helena Largest city Billings Area  Ranked 4th  - Total 147,165 sq mi (381,156 km²)  - Width 255 miles (410 km)  - Length 630 miles (1,015 km)  - % water 1  - Latitude 44°26N to 49°N  - Longitude 104°2W to 116°2W Population  Ranked... This article does not adequately cite its references or sources. ... Official language(s) English Capital Cheyenne Largest city Cheyenne Area  Ranked 10th  - Total 97,818 sq mi (253,348 km²)  - Width 280 miles (450 km)  - Length 360 miles (580 km)  - % water 0. ... Motto: Fortis et liber (Latin: Strong and free) Official languages English (see below) Flower   Wild rose Tree Lodgepole Pine Bird Great Horned Owl Capital Edmonton Largest city Calgary Lieutenant-Governor Norman Kwong Premier Ed Stelmach (PC) Parliamentary representation  - House seats  - Senate seats 28 6 Area Total  - Land  - Water  (% of total... Motto: Splendor Sine Occasu (Latin: Splendour without diminishment) Official languages English Capital Victoria Largest city Vancouver Lieutenant-Governor Iona Campagnolo Premier Gordon Campbell (BC Liberal) Parliamentary representation  - House seats  - Senate seats 36 6 Area Total  - Land  - Water  (% of total)  Ranked 5th 944,735 km² 925,186 km² 19,549 km... Motto: Multis E Gentibus Vires (Latin: From many peoples strength) Capital Regina Largest city Saskatoon Official languages English Government - Lieutenant-Governor Gordon Barnhart - Premier Lorne Calvert (NDP) Federal representation in Canadian Parliament - House seats 14 - Senate seats 6 Confederation September 1, 1905 (Split from NWT) (9th (province)) Area Ranked 7th...


Geologists know the exact chemical composition of this tephra (which they call Mazama ash) and both geologists and archeologists use the distinctive layer it formed in relative dating. As with all tephra layers, Mazama ash is thickest near its source (20 feet (6 m)) and becomes thinner with increasing distance from its source (70 miles, 110 km northwest it is 1 foot (0.3 m) thick). the are cool The Geologist by Carl Spitzweg A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system (see planetary geology). ... Archaeology or sometimes in American English archeology (from the Greek words αρχαίος = ancient and λόγος = word/speech) is the study of human cultures through the recovery, documentation and analysis of material remains, including architecture, artefacts, biofacts, human remains, and landscapes. ... Before the advent of absolute dating in the 20th century, archaeologists and geologists were largely limited to the use of Relative Dating techniques. ...


Pyroclastic flow material near Mazama remained extremely hot for months, and in some places they were more than 250 feet (76 m) deep. Hot gases escaping from the cooling deposits tended to follow vertical channels and emerged at the surface as fumaroles. Over time these gases cemented the channels, which are now exposed as very tall vertical columns and spires of tuff (good examples are along the upper walls of Sand Creek Canyon and Annie Canyon). Sulfur deposits near a fumarole A fumarole (Latin fumus, smoke) is an opening in Earths (or any other astronomical bodys) crust, often in the neighborhood of volcanoes, which emit steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ...


Post-collapse phase

All volcanic activity on Mazama since its collapse has been within the caldera. The first significant eruptive period of this phase created an andesite lava platform that raises 1200 feet (365 m) above the caldera floor (it is called the 'central platform'). Latter eruptions created cinder cones such as Wizard Island (c. 6,000 years old and 763 feet, 233 m high) and Merriam Cone and also rhyodacite domes (most of these features are under water). USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Wizard Island lies in Crater Lake. ...


Over time much of the c.4,000 foot (c.1,200 m) depth of the caldera was filled with volcanic material. The rest was filled with water from snowmelt and rain to eventually form Crater Lake. Crater Lake is 1,958 feet (597 m) deep, making it the second deepest lake in North America (after Canada's Great Slave Lake). Its great depth and purity absorbs all colors of visible light except blue, giving the lake its characteristic indigo hue. Animation of snowcover changing with the seasons Snow is precipitation in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. ... Rain is a source of precipitation which forms when separate drops of water fall to the Earths surface from clouds. ... Crater Lake is a caldera lake in the U.S. state of Oregon. ... World map showing North America A satellite composite image of North America. ... Mackenzie River drainage basin showing Great Slave Lakes position in the Western Canadian Arctic Great Slave Lake (French: Grand lac des Esclaves) is the second largest lake in the Northwest Territories of Canada (behind Great Bear Lake), the deepest lake in North America at 614 meters (2,015 ft. ... Color is an important part of the visual arts. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... For other uses, see Blue (disambiguation). ... Indigo (or spectral indigo) is the color on the spectrum between 440 and 420 nanometres in wavelength, placing it between blue and violet. ...


Future Activity

Features beneath the surface of Crater Lake constructed using data from the 2000 bathymetry survey. Colors range from orange to blue with increasing water depth.
Features beneath the surface of Crater Lake constructed using data from the 2000 bathymetry survey. Colors range from orange to blue with increasing water depth.

Assuming no large eruptions destroy it first, Crater Lake will eventually be destroyed when erosion breaches the caldera rim and the lake escapes as a massive flood. Future eruptions will probably continue to follow the post-collapse pattern of being confined to the caldera. Additional cinder cones and lava flows will likely issue from fissures on the lakebed; some will be totally under water, while others may reach the surface to create new islands and peninsulas. Lava flows may build-up over time, reducing the lake's depth and may eventually divide it into more than one body of water (this happened to Newberry Caldera). USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... USGS image from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Severe soil erosion in a wheat field near Washington State University, USA. For erosion as understood by materials science, see Erosion (materials science) For erosion as an English analogy, see Erosion (figurative) For erosion as an operation of Mathematical morphology, see Erosion (morphology) Erosion is the displacement of solids (soil... Picture of flooding in Amphoe Sena, Ayutthaya Province, Thailand For other uses, see Flood (disambiguation). ... A peninsula in Croatia A peninsula (from the latin words paene insula, almost island) is a geographical landform consisting of an extension of a body of land from a larger body of land, surrounded by water on three sides. ... Newberry Caldera, with Paulina Lake, East Lake, and Big Obsidian Flow Newberry Caldera is the caldera on Newberry Volcano, a shield volcano in central Oregon. ...


Less likely would be the resumption of cone-building activity and the creation of a coalescing chain of small stratovolcanoes. These could, in time, merge to reform Mazama to an approximation of its former glory. Even less likely would be a repeat of the cataclysmic eruption that formed the caldera (however, recent Mazama lavas do show an increase in silica content, so this still is a possibility).


References

  • USGS Geonames. Retrieved on September 22, 2006.
  • Stephen L. Harris; Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X
  • Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle; Geology of National Parks: Fifth Edition, (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7

September 22 is the 265th day of the year in the Gregorian calendar (266th in leap years). ... For the Manfred Mann album, see 2006 (album). ...

External links

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  Results from FactBites:
 
Mount Mazama - Wikipedia, the free encyclopedia (1915 words)
Mount Mazama is a destroyed stratovolcano in the Oregon part of the Cascade Range.
Mazama's final act started with a large eruption that sent a mile (1.6 km) wide column of hot tephra 5 to 10 miles (8 to 16 km) into the sky at almost twice the speed of sound.
As with all tephra layers, Mazama ash is thickest near its source (20 feet (6 m)) and becomes thinner with increasing distance from its source (70 miles, 110 km northwest it is 1 foot (0.3 m) thick).
  More results at FactBites »

 
 

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