Mount Mazama

Mount Mazama

Overview
Mount Mazama is a destroyed stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 part of the Cascade Volcanic Arc
Cascade Volcanoes
The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi ...

 and the Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...

. The volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

's collapsed caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 holds Crater Lake
Crater Lake
Crater Lake is a caldera lake located in the south-central region of the U.S. state of Oregon. It is the main feature of Crater Lake National Park and famous for its deep blue color and water clarity. The lake partly fills a nearly deep caldera that was formed around 7,700 years agoby the...

, and the entire mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

 is located within Crater Lake National Park
Crater Lake National Park
Crater Lake National Park is a United States National Park located in southern Oregon. Established in 1902, Crater Lake National Park is the sixth oldest national park in the United States and the only one in the state of Oregon...

.

Mazama was destroyed by a volcanic eruption that occurred around 5,677 (± 150) BC. The eruption reduced Mazama's approximate 12000 feet (3,657.6 m) height by around a mile (1600 m). Much of the volcano fell into the volcano's partially emptied neck and magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...

.
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Encyclopedia
Mount Mazama is a destroyed stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 part of the Cascade Volcanic Arc
Cascade Volcanoes
The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi ...

 and the Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...

. The volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

's collapsed caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 holds Crater Lake
Crater Lake
Crater Lake is a caldera lake located in the south-central region of the U.S. state of Oregon. It is the main feature of Crater Lake National Park and famous for its deep blue color and water clarity. The lake partly fills a nearly deep caldera that was formed around 7,700 years agoby the...

, and the entire mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

 is located within Crater Lake National Park
Crater Lake National Park
Crater Lake National Park is a United States National Park located in southern Oregon. Established in 1902, Crater Lake National Park is the sixth oldest national park in the United States and the only one in the state of Oregon...

.

Mazama was destroyed by a volcanic eruption that occurred around 5,677 (± 150) BC. The eruption reduced Mazama's approximate 12000 feet (3,657.6 m) height by around a mile (1600 m). Much of the volcano fell into the volcano's partially emptied neck and magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...

. At 8,159 feet (2,487 m), Hillman Peak is now the highest point on the rim.

History


The Klamath Native Americans of the area believed that the mountain was inhabited by Llao
Llao
Llao is the god of the underworld in the mythology of the Klamath Native American tribe. Llao fought a great battle with the sky god, Skell, which caused the eruption of Mount Mazama, creating Crater Lake.-Llao and Skell:...

, their god
God
God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....

 of the underworld
Underworld
The Underworld is a region which is thought to be under the surface of the earth in some religions and in mythologies. It could be a place where the souls of the recently departed go, and in some traditions it is identified with Hell or the realm of death...

. After the mountain destroyed itself the Klamaths recounted the events as a great battle between Llao and his rival Skell, their sky god.

Much of what is known of Mazama's geology comes from a study by Howel Williams
Howel Williams
Howel Williams was a noted American geologist and volcanologist. He was born of Welsh parents in Liverpool, England, on October 12, 1898. He received a BA in geography in 1923 and an MA in archaeology in 1924 from Liverpool University. He studied geology at the Imperial College of Science and...

 of the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

 and later, from USGS geologist Charles R. Bacon
Charles R. Bacon
Charles R. Bacon is an American geologist at the United States Geological Survey in the Volcano Hazards Team who has done a tremendous amount of work on Crater Lake National Park's geology....

 who expanded and modified Williams' work.

Name


Mount Mazama was given its name in 1896 when a climbing club from Portland, The Mazamas
The Mazamas
The Mazamas is a mountaineering club based in Portland, Oregon, United States, founded in 1894.-Name:The name Mazamas means mountain goat, from Nahuatl mazatl, deer. for etymology...

, organized a visit to Crater Lake
Crater Lake
Crater Lake is a caldera lake located in the south-central region of the U.S. state of Oregon. It is the main feature of Crater Lake National Park and famous for its deep blue color and water clarity. The lake partly fills a nearly deep caldera that was formed around 7,700 years agoby the...

, and named the lost peak Mount Mazama after their own club; the name being derived from a Native American one, meaning "mountain goat."

Growth phase


Mazama started to grow around 400,000 years ago in the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

, mainly from lava flows interbedded 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 volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...

es 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 cone
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

s.

Cone building eruptions lasted until around 50,000 years ago when andesite lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 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 11000 feet (3,352.8 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
Mount Shasta
Mount Shasta is located at the southern end of the Cascade Range in Siskiyou County, California and at is the second highest peak in the Cascades and the fifth highest in California...

.

Silica enrichment


After its cone building phase, Mazama lavas became increasingly silica-rich and viscous - two conditions that tend to trap explosive gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es. The first major eruption in this new cycle of Mazama's life occurred about 10,000 years later, when dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...

 flows high on the volcano's southwest face formed a series of domes. These structures were subsequently destroyed by either collapse or steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

 explosions (see phreatic eruption
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...

). Either way, their destruction created large landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

s that left deposits at the head of Munson Valley and as far away as Devils Backbone.

Mazama's next major eruptive period occurred between 25,000 and 30,000 years ago and extruded rhyodacite
Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate...

 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 feet (182.9 m) high Redcloud Cliff (later cut in two by caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 subsidence) and a dome above what today is Steel Bay.

The volcano then went dormant for roughly the next 20,000 years, while successive ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

 glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

s (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.

Explosive phase


Around 5677 BC Mazama awoke from its slumber with explosive rhyodacite
Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate...

 eruptions on the northern part of the main summit where Llao Rock now resides. Great quantities of pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 and ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

 were ejected as a large crater was excavated by the explosions. The tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

 was carried by prevailing winds to the east and southeast. Associated with this was a pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

 that was 1.25 mi (2 km) wide, 1200 feet (365.8 m) thick at its deepest point, and contained 0.25 cu mi (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).

One to two hundred years later (based on radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

) 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.

Mazama's final act started with a large eruption that sent a mile (1.6 km) wide column of hot tephra 5 to 10 mi (8 to 16.1 km) into the sky at almost twice the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

. 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 Wineglass Welded Tuff. Flow after flow followed in rapid succession, stressing the ability of Mazama's magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...

 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 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
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 valleys and in some cases not coming to rest for 40 miles (64.4 km). As the eruptions were occurring Mazama was imploding.

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
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. Also, the sudden and dramatic reduction in overpressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 on the remaining gas charged molten rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 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.

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 andesitic scoria
Scoria
Scoria is a volcanic rock containing many holes or vesicles. It is most generally dark in color , and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity...

, 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
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 lapilli and crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

-rich ash up to 50 feet (15.2 m) thick on the newly formed caldera rim.

In the end an estimated 11 to 14 cu mi (45.9 to 58.4 km3) of magma escaped from Mazama's magma chamber during this eruptive cycle as approximately 25 cu mi (104.2 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. At that time, Mazama was about 1 miles (1,609.3 m) shorter than its initial height of approximately 12000 feet (3,657.6 m).

Aftermath


Hundreds of square kilometers of the surrounding countryside were destroyed by material ejected from the collapse and associated eruptions. One pyroclastic flow traveled 40 miles (64.4 km) from Mazama down Rogue River Valley while another moved north in-between Mount Bailey
Mount Bailey (Oregon)
Mount Bailey is a relatively young tephra cone and shield volcano in the Cascade Range, located on the opposite side of Diamond Lake from Mount Thielsen in southern Oregon, United States. Bailey consists of a high main cone on top of an old basaltic andesite shield volcano. With a volume of ,...

 and Mount Thielsen
Mount Thielsen
Mount Thielsen, or Big Cowhorn, is an extinct shield volcano in the Oregon High Cascades, near Mount Bailey. Because Mount Thielsen stopped erupting 250,000 years ago, glaciers have heavily eroded the volcano's structure, creating precipitous slopes and its horn-like peak...

, moving over Diamond Lake
Diamond Lake (Oregon)
Diamond Lake is a lake in the southern part of the U.S. state of Oregon. It lies near the junction of Oregon Route 138 and Oregon Route 230 in the Umpqua National Forest in Douglas County. It is located between Mount Bailey to the west and Mount Thielsen to the east; it is just north of Crater Lake...

 (it finally came to rest in North Umpqua River
North Umpqua River
The North Umpqua River is a tributary of the Umpqua River, approximately long, in southwestern Oregon in the United States. It drains a scenic and rugged area of the Cascade Range southwest of Eugene, flowing through steep canyons and surrounded by large Douglas-fir forests...

 valley). Winds carried tephra (ash and pumice) from Mazama northeast, where it covered over 500000 sq mi (1,294,994.1 km²) including nearly all of Oregon, Washington, northern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

, Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

, western Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, and parts of Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

, Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

, Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

, Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...

, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, and Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

.

Geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...

s know the exact chemical composition of this tephra (which they call Mazama Ash
Mazama Ash
The Mazama Ash is a large geologically recent volcanic ash deposit that covers portions of the U.S. states of California, Oregon, Washington, Idaho, Montana, Nevada, Wyoming and Utah, as well as the Canadian provinces of British Columbia, Alberta and southwestern Saskatchewan...

) and both geologists and archeologists use the distinctive layer it formed in the specific techniques of relative dating
Relative dating
Relative dating is the science determining the relative order of past events, without necessarily determining their absolute age.In geology rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another...

 called tephrochronology
Tephrochronology
250px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at the height of the [[volcanologists]] hands is [[rhyolitic]] [[tephra]] from [[Hekla]]....

. As with all tephra layers, Mazama ash is thickest near its source (20 feet (6.1 m)) and becomes thinner with increasing distance from its source. 70 miles (112.7 km) northwest it is 1 feet (30.5 cm) thick.

Deposits of pyroclastic flow material near Mazama remained extremely hot for months, and in some places they were more than 250 feet (76.2 m) deep. Hot gases escaping from the cooling deposits tended to follow vertical channels and emerged at the surface as fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...

s. Over time these gases cemented the channels, which are now exposed as very tall vertical columns and spires of tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...

 (good examples are along the upper walls of Sand Creek Canyon and Annie Canyon).

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 (the 'central platform') that rises 1,200 feet (365 m) above the caldera floor. Later eruptions created cinder cones such as Wizard Island
Wizard Island
Wizard Island is a volcanic cinder cone which forms an island at the west end of Crater Lake in Crater Lake National Park, Oregon. The top of the island reaches above sea level, about above the average surface of the lake. The cone is capped by a volcanic crater about wide and deep. The...

 (c. 6,000 years old and 763 feet (232.6 m) high) and Merriam Cone and also rhyodacite domes (most of these features are under water).

Over time much of the approximate 4000 feet (1,219.2 m) depth of the caldera was filled with volcanic material. Part of the remainder was filled with water from snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

melt and rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

 to eventually form Crater Lake
Crater Lake
Crater Lake is a caldera lake located in the south-central region of the U.S. state of Oregon. It is the main feature of Crater Lake National Park and famous for its deep blue color and water clarity. The lake partly fills a nearly deep caldera that was formed around 7,700 years agoby the...

. Crater Lake reaches a maximum depth of 1,958 feet (597 m), making it the second deepest lake in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 (after Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

's Great Slave Lake
Great Slave Lake
Great Slave Lake is the second-largest lake in the Northwest Territories of Canada , the deepest lake in North America at , and the ninth-largest lake in the world. It is long and wide. It covers an area of in the southern part of the territory. Its given volume ranges from to and up to ...

). The lake's great depth and purity causes it to absorb all color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

s of visible light except blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...

, resulting in its characteristic indigo
Indigo
Indigo is a color named after the purple dye derived from the plant Indigofera tinctoria and related species. The color is placed on the electromagnetic spectrum between about 420 and 450 nm in wavelength, placing it between blue and violet...

 hue.

Future activity


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 peninsula
Peninsula
A peninsula is a piece of land that is bordered by water on three sides but connected to mainland. In many Germanic and Celtic languages and also in Baltic, Slavic and Hungarian, peninsulas are called "half-islands"....

s. 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 the Newberry Caldera).

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 size. 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 is still a possibility).