View allAll Photos Tagged StratoVolcanoes
earth science, geology, geomorphology, landscape, cushion plant, azorella compacta, llareta, altiplano, volcano, volcanoes, vulcanology, igneous, volcanic, stratovolcano, composite volcano, avalanche debris, parinacota, pomerape, lauca national park, national park, unesco, man and biosphere reserve, mab, chile, south america
From this vantage and with the cloud it’s just barely possible to see the resurgent dome, but it has been building and falling, building and falling ever since 1980. Given enough time it should eventually refill the crater and possibly even rebuild the peak. This is entirely in the nature of stratovolcanoes. 29 years is not even a heartbeat on a geologic scale
Mount Redoubt, one of our resident active stratovolcanoes, appears frozen into stillness as it floats above a sea of clouds.
The Cascade Lakes Scenic Byway passes through a volcanic and glacial landscape of incredible diversity and tremendous significance.
Diverse landforms as stratovolcanoes, shield volcanoes, cinder cones, sheets of pumice and ash, sheets of ash-flow tuffs, maars, caves, and several kinds of lava flows and domes.
Nestled merely 16 kilometers from the picturesque city of Antigua in Guatemala, Volcán de Fuego (“Volcano of Fire”) stands as a formidable sentinel in the mesmerizing landscape. A distinguished member of the three large stratovolcanoes that loom over Antigua, this geological marvel is an integral part of the Ring of Fire—an arc of volcanoes and seismic fault lines defining the region's dynamic tectonic canvas. Yet Volcán de Fuego boasts a historical tapestry rich with over 60 eruptions since 1524, claiming the title of Central America's most historically active volcano. The catastrophic eruption of June 3, 2018 etched a recently somber reminder of this volcano’s presence, compelling the evacuation of 3,100 residents and the loss of approximately 165 lives. Volcán de Fuego remains active with daily explosions and ash fall. However, the resilient spirit and cultural heritage of the Guatemalan people are intricately intertwined with these volatile forces of nature. The Mayan culture depicts volcanoes as embodying a dualistic symbolism of powerful entities capable of both destruction and nourishment. This is seen in the rich agriculture and fertile soils that fuel Antigua’s flourishing coffee production. This photograph captures not just the formidable presence of Volcán de Fuego, but also the complex interplay between nature's fury and the unwavering spirit of a community that finds resilience and sustenance amidst the shadows of adversity.
Purpose of the trip: The trip to Guatemala was one taken as a global medical initiative to provide healthcare and education to impoverished regions of Guatemala. Partnering with local programs and clinics in the country, this endeavor was a testament to the commitment to not only broaden healthcare access, but to form enduring connections with the communities served as well. The makeshift clinics each day, set up in school classrooms and community centers, offered a spectrum of services—ranging from physical exams, urinalysis, blood glucose checks, to ultrasounds, steroid injections, pelvic exams, and medication and eyeglasses administration. The majority seeking care at these clinics were women, children, and the elderly, as many of the men were often absent due to daytime work toiling in fields or managing storefronts.
Ashley Piwkiewicz
I love this song: www.youtube.com/watch?v=IJR81_wpOrI&feature=related which one (for me) perfectly suit this photo... Enjoy!
The highest peak in Arizona at 12,637 feet (3,852 m) high is Humphreys Peak, a part of the San Francisco Peaks. These peaks are a string of extinct volcanoes that are called Stratovolcanoes, grouped in with Vesuvius and Krakatoa...
photo by jadoretotravel
How often does one get the opportunity of climbing a real volcano and shooting a selfie on top of the caldera. With toxic fumes and an a toxic pond in the background?
The Ijen volcano complex is a group of stratovolcanoes, in East Java, Indonesia. It is inside a larger caldera Ijen, which is about 20 kilometers wide. The Gunung Merapi stratovolcano is the highest point of that complex. The name of this volcano resembles that of a different volcano, Mount Merapi in central Java, also known as Gunung Merapi. The name "Merapi" means "fire" in the Indonesian language. From: wiki.
Java is the world's most densely populated island (population: 136 million). It is home to 60% of Indonesia's population. Much of Indonesian history took place on Java; it was the centre of powerful Hindu-Buddhist empires, Islamic sultanates, the core of the colonial Dutch East Indies, and was at the centre of Indonesia's campaign for independence. The island dominates Indonesian social, political and economic life. More information on wikipedia.
Villarrica is one of Chile's most active volcanoes, rising above the lake and town of the same name, 750 km (470 mi) south of Santiago. It is also known as Rucapillán, a Mapuche word meaning "Pillan's house". It is the westernmost of three large stratovolcanoes that trend NW-SW obliquely perpendicular to the Andean chain along the Mocha-Villarrica Fault Zone, along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park. Guided ascents are popular during summer months.
Villarrica, with its lava of basaltic-andesitic composition, is one of a small number worldwide known to have an active (but in this case intermittent) lava lake within its crater. The volcano usually generates strombolian eruptions with ejection of incandescent pyroclasts and lava flows. Rainfall plus melted snow and glacier ice can cause massive lahars (mud and debris flows), such as during the eruptions of 1964 and 1971.
Villarrica is one of 9 volcanoes currently monitored by the Deep Earth Carbon Degassing Project. The project is collecting data on the carbon dioxide and sulphur dioxide emission rates from subaerial volcanoes.
Arequipa - Mirador de vólcanes
Sabancaya is an active 5,976-metre (19,606 ft) stratovolcano in the Andes of southern Peru. It is the most active volcano in Peru and is part of a 20-kilometre (12 mi) north-south chain of three major stratovolcanoes
Puedes conocer más sobre Perú entrando a mi álbum Peruvian Marvels
Aerial view of the massive debris avalanche on the northwest side of Mt. Shasta. All the hummocks are building-sized blocks of Mt. Shasta. This huge prehistoric sector collapse is one of the largest landslides known on Earth and dramatically illustrates one of the main hazards around stratovolcanoes.
The Hakkōda Mountains (八甲田山系 Hakkōda-sankei) is a volcanic complex that lies to the south of Aomori in Aomori Prefecture, Japan. The range consists of more than a dozen stratovolcanoes and lava domes arranged into two volcanic groups.[1] The Northern Hakkōda Volcanic Group emerges from the rim of an 8-km wide caldera that dates back to the Pleistocene.[1] The Southern Hakkōda Volcanic Group predates the caldera.[2]
The highest peak in the range is Mount Ōdake, which can be climbed from Sukayu Onsen in about four hours. Heavy snowfall makes Hakkoda a prime destination for backcountry and mountain skiers, and there are two mountain huts for overnight trips. The lower slopes of the mountains are forested interspersed with moorland. Above 1300 meters,[3] the Alpine climate zone starts.
The Hakkōda Mountains, along with Lake Towada and the Oirase Valley make up the Towada-Hachimantai National Park.[3]
(series of still images from the Westdahl Peak web camera on Unimak Island, Alaska)
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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Thirteen episodes of subsequent explosive ash eruptions took place on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 24 to 25 September, 3 October, and 2-3 November 2023. Seen here is Shishaldin with a steam plume in the morning of 25 November 2023.
The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic. Shishaldin's erupted materials in 2023 have been mafic (basaltic).
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Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
Snow covered Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. The volcano is also known as Rucapillán, a Mapuche word meaning "House of the Spirit". It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. Villarrica is one of only a handful of volcanoes worldwide to have an active lava lake within its crater. About 25 scoria cones dot Villarica's flanks. It also has volcanic caves.
This seismogram is from the Korovin Volcano seismic station on Atka Island in Alaska's Aleutian Islands. The noise is from a volcanic explosion at the summit of Korovin Volcano at 10:33 AM, local time, on 15 April 2025. Korovin Volcano is a subduction zone stratovolcano near the northern edge of eastern Atka Island.
The Aleutian Arc formed by subduction of the Pacific Plate under the Bering Plate (often considered to be part of the North American Plate).
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Info. from the Alaska Volcano Observatory (AVO):
A small, short-lived explosion was detected at the Atka volcanic complex this morning at 10:34 Alaska Daylight Time [sic] April 25 (18:34 Universal Time April 25) in local infrasound and seismic data. Processing of the local infrasound data indicates the explosion originated from the summit crater of Korovin, one of several volcanoes within the Atka volcanic complex. AVO is increasing the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY.
High clouds blocked the area at the time of the explosion, preventing satellite observations. Similar past events at the Atka volcanic complex did not result in a noticeable ashfall or ash cloud or other impacts.
The Atka volcanic complex forms the northern part of Atka Island, located about 16 kilometers north of the community of Atka and 1,761 kilometers southwest of Anchorage. The Atka volcanic complex includes a possible older caldera and several younger vents, including Korovin Volcano, Mount Kliuchef, and Sarichef Volcano. Korovin Volcano, a 1553-meter-high (5030 feet) stratovolcano, has been the site of most historical volcanic activity, and has a small, roiling crater lake that occasionally produces energetic steam emissions. Korovin has erupted several times in the past 200 years, including 1973, 1987, and 1998, and has likely had small ash emissions as recently as 2005. Typical recent Korovin eruptions produce minor amounts of ash and occasional but small lava flows. Reports of the height of the ash plume produced by the 1998 eruption ranged as high as 10,600 meters (35,000 feet) above sea level. Mount Kliuchef is composed of a series of five vents aligned northeast–southwest. The two main summit vents of Kliuchef appear relatively young and the easternmost was probably the source of an 1812 eruption that is sometimes attributed to Sarichef.
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Info. at:
en.wikipedia.org/wiki/Korovin_Volcano
and
(still image from the Brown Peak web camera on Unimak Island, Alaska)
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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Thirteen episodes of subsequent explosive ash eruptions took place on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 24 to 25 September, 3 October, and 2-3 November 2023. Seen here is Shishaldin with a steam plume in the morning of 19 November 2023.
The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic. Shishaldin's erupted materials in 2023 have been mafic (basaltic).
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Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
Mt. Hood is a subduction zone stratovolcano in northwestern Oregon. It is part of the north-south trending Cascade Range of volcanoes from northern California to southwestern British Columbia. Other famous Cascade volcanoes include Mt. St. Helens, Mt. Rainier, Mt. Shasta, and Mt. Mazama (now Crater Lake Caldera).
Mt. Hood area volcanism started in the Middle Miocene, 8 to 10 million years ago, just after Columbia River Flood Basalt volcanism. Miocene and Pliocene andesites and basalts cap topographic ridges in the Mt. Hood area. During the Late Pliocene (sensu traditio), at 3 to 1.3 million years ago, the Sandy Glacier Volcano occupied the site of the current Mt. Hood. Sandy Glacier Volcano is now mostly buried by the modern Mt. Hood volcanic cone. Mt. Hood itself is less than 730,000 years old - all of its rocks have modern magnetic signatures. Lavas and other eruptive materials are high-silica andesites and low-silica dacites. 70% of the Mt. Hood cone consists of lava flows, while the remaining 30% is volcaniclcastic deposits. The modern cone is less than 300,000 years old. Near the summit of Mt. Hood are lava flows dating to younger than 200,000 years old.
Unlike nearby Mt. St. Helens, Mt. Hood is much older and has had little explosive activity. Most of Mt. Hood's volcanism has consisted of andesite lava flows and dome-building. Few explosive events have occurred through time here - few tephra deposits have a Mt. Hood source.
Mt. Hood rocks are often porphyritic two-pyroxene andesites, plus a little olivine. There's been little chemical variation in Mt. Hood lavas through time. Because of this, individual lava flows are difficult to date based on lithology - they're all the same. Much of Mt. Hood itself consists of hydrothermally-altered rocks.
Names are assigned to the various eruptive phases in Mt. Hood's history. The Polallie eruptive phase occurred from 12 to 25 thousand years ago. The Timberline eruptive phase occurred ~1500 years ago. The Old Maid eruptive phase occurred over 200 years ago, often dated to 1780-1801 A.D. Dome building occurred from 1781 to 1793. During that time, periodic, relatively small eruptions occurred.
Because Mt. Hood is a snow-clad volcano, activity results in melting of snow and mobilization of loose materials. Rainstorms could also mobilize loose debris in the area. Mt. Hood lahars have probably formed by both mechanisms.
The watercourse at the bottom of the picture is the Sandy River.
Locality: Mt. Hood Volcano (looking east from the Jonsrud Viewpoint in the town of Sandy), northwestern Oregon, USA
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Info. at:
Villarrica is one of Chile's most active volcanoes, rising above the lake and town of the same name, 750 km (470 mi) south of Santiago. It is also known as Rucapillán, a Mapuche word meaning "Pillan's house". It is the westernmost of three large stratovolcanoes that trend NW-SW obliquely perpendicular to the Andean chain along the Mocha-Villarrica Fault Zone, along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park. Guided ascents are popular during summer months.
Villarrica, with its lava of basaltic-andesitic composition, is one of a small number worldwide known to have an active (but in this case intermittent) lava lake within its crater. The volcano usually generates strombolian eruptions with ejection of incandescent pyroclasts and lava flows. Rainfall plus melted snow and glacier ice can cause massive lahars (mud and debris flows), such as during the eruptions of 1964 and 1971.
Villarrica is one of 9 volcanoes currently monitored by the Deep Earth Carbon Degassing Project. The project is collecting data on the carbon dioxide and sulphur dioxide emission rates from subaerial volcanoes (Wikipedia)
This is an example of a stratovolcano just like Mt. Hekla.
Where the two plates meet, sometimes one moves down, while the other moves upward. As the plate that is moving down is forced deeper, parts of it begin to melt and form magma that rises to the surface, often in explosive eruptions. The plate that rises, tends to create large, classic, cone-shaped volcanoes called stratovolcanoes, such as Mt. Hekla.
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Explain why the eruption happened>
It is most likely that the eruptio happened because the tetonic plates that meet in Iceland and sometimes split apart with terrific results. Sometimes the plated go in different directions, up and down, but sometimes they move in different direction rubbing against one another. When a plate moves down (subduction), being forced deep, part of it begin to melt and form magma that rises to the surface, often in explosive eruptions. Subduction zones tend to create large, classic, cone-shaped volcanoes called stratovolcanoes, such as Mt. Hekla.
This is a view of the eroded remains of the Late Eocene-aged Guffey Volcanic Center, which consisted of coalesced stratovolcanoes. The volcanic rocks are mostly alkaline, including the scarce lava type shoshonite. The rocks date to about 36 million years ago.
The prominent peak at left is McIntyre Mountain. The peak at ~center is Castle Mountain. The somewhat flat-topped mountain at the far-right is Thirtynine Mile Mountain. The double-humped mountain just in front of that is Saddle Mountain. These mountains have lava flows and lahars (volcanic mudflows) that were originally on the flanks of the Guffey Volcanic Center's stratovolcano complex.
Locality: Thirtynine Mile Volcanic Field overlook at Cripple Creek Granite outcrop, northern side of Guffey Road (= Rt. 102), about 2.7 road-miles west of the Guffey Road-Rt. 11 intersection, southeastern Park County, central Colorado, USA (looking from ~38º 46’ 09.64” North latitude, ~105º 20’ 12.31” West longitude)
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Most info. from:
Meyer et al. (2004) - Field guide to the paleontology and volcanic setting of the Florissant fossil beds, Colorado. Geological Society of America Field Guide 5: 151-166.
(still image from the Brown Peak web camera on Unimak Island, Alaska)
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Shishaldin Volcano is a subduction zone stratovolcano on Unimak Island in the Aleutian Islands of Alaska. Minor lava eruptions in the summit crater started on 12 July 2023. Thirteen episodes of subsequent explosive ash eruptions took place on 14 July, 15 July, 18 July, 22-23 July, 25-26 July, 4 August, 14-15 August, 25 August, 5 September, 15 September, 24 to 25 September, 3 October, and 2-3 November 2023. Seen here is Shishaldin with a steam plume in the morning of 25 November 2023.
The Aleutian Arc is a subduction zone formed as the Pacific Plate dives underneath the North American Plate (this area is sometimes called the Bering Plate). The diving plate in subduction zones releases water at depth, which causes partial melting of overlying mantle rocks. The low-density melt rises and eventually reaches the surface, forming volcanoes. All subduction zones have volcanoes and frequent seismicity. Volcanoes in such settings tend to have explosive ash eruptions. Rocks and tephra deposits at subduction zone volcanoes are usually intermediate in composition - typically andesitic to dacitic. Shishaldin's erupted materials in 2023 have been mafic (basaltic).
-------------------------------------------
Info. at:
en.wikipedia.org/wiki/Mount_Shishaldin
and
Mt. Hood is a subduction zone stratovolcano in northwestern Oregon. It is part of the north-south trending Cascade Range of volcanoes from northern California to southwestern British Columbia. Other famous Cascade volcanoes include Mt. St. Helens, Mt. Rainier, Mt. Shasta, and Mt. Mazama (now Crater Lake Caldera).
Mt. Hood area volcanism started in the Middle Miocene, 8 to 10 million years ago, just after Columbia River Flood Basalt volcanism. Miocene and Pliocene andesites and basalts cap topographic ridges in the Mt. Hood area. During the Late Pliocene (sensu traditio), at 3 to 1.3 million years ago, the Sandy Glacier Volcano occupied the site of the current Mt. Hood. Sandy Glacier Volcano is now mostly buried by the modern Mt. Hood volcanic cone. Mt. Hood itself is less than 730,000 years old - all of its rocks have modern magnetic signatures. Lavas and other eruptive materials are high-silica andesites and low-silica dacites. 70% of the Mt. Hood cone consists of lava flows, while the remaining 30% is volcaniclcastic deposits. The modern cone is less than 300,000 years old. Near the summit of Mt. Hood are lava flows dating to younger than 200,000 years old.
Unlike nearby Mt. St. Helens, Mt. Hood is much older and has had little explosive activity. Most of Mt. Hood's volcanism has consisted of andesite lava flows and dome-building. Few explosive events have occurred through time here - few tephra deposits have a Mt. Hood source.
Mt. Hood rocks are often porphyritic two-pyroxene andesites, plus a little olivine. There's been little chemical variation in Mt. Hood lavas through time. Because of this, individual lava flows are difficult to date based on lithology - they're all the same. Much of Mt. Hood itself consists of hydrothermally-altered rocks.
Names are assigned to the various eruptive phases in Mt. Hood's history. The Polallie eruptive phase occurred from 12 to 25 thousand years ago. The Timberline eruptive phase occurred ~1500 years ago. The Old Maid eruptive phase occurred over 200 years ago, often dated to 1780-1801 A.D. Dome building occurred from 1781 to 1793. During that time, periodic, relatively small eruptions occurred.
Because Mt. Hood is a snow-clad volcano, activity results in melting of snow and mobilization of loose materials. Rainstorms could also mobilize loose debris in the area. Mt. Hood lahars have probably formed by both mechanisms.
Locality: Mt. Hood Volcano (looking east from the Jonsrud Viewpoint in the town of Sandy), northwestern Oregon, USA
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Info. at:
Mt. Hood is a subduction zone stratovolcano in northwestern Oregon. It is part of the north-south trending Cascade Range of volcanoes from northern California to southwestern British Columbia. Other famous Cascade volcanoes include Mt. St. Helens, Mt. Rainier, Mt. Shasta, and Mt. Mazama (now Crater Lake Caldera).
Mt. Hood area volcanism started in the Middle Miocene, 8 to 10 million years ago, just after Columbia River Flood Basalt volcanism. Miocene and Pliocene andesites and basalts cap topographic ridges in the Mt. Hood area. During the Late Pliocene (sensu traditio), at 3 to 1.3 million years ago, the Sandy Glacier Volcano occupied the site of the current Mt. Hood. Sandy Glacier Volcano is now mostly buried by the modern Mt. Hood volcanic cone. Mt. Hood itself is less than 730,000 years old - all of its rocks have modern magnetic signatures. Lavas and other eruptive materials are high-silica andesites and low-silica dacites. 70% of the Mt. Hood cone consists of lava flows, while the remaining 30% is volcaniclcastic deposits. The modern cone is less than 300,000 years old. Near the summit of Mt. Hood are lava flows dating to younger than 200,000 years old.
Unlike nearby Mt. St. Helens, Mt. Hood is much older and has had little explosive activity. Most of Mt. Hood's volcanism has consisted of andesite lava flows and dome-building. Few explosive events have occurred through time here - few tephra deposits have a Mt. Hood source.
Mt. Hood rocks are often porphyritic two-pyroxene andesites, plus a little olivine. There's been little chemical variation in Mt. Hood lavas through time. Because of this, individual lava flows are difficult to date based on lithology - they're all the same. Much of Mt. Hood itself consists of hydrothermally-altered rocks.
Names are assigned to the various eruptive phases in Mt. Hood's history. The Polallie eruptive phase occurred from 12 to 25 thousand years ago. The Timberline eruptive phase occurred ~1500 years ago. The Old Maid eruptive phase occurred over 200 years ago, often dated to 1780-1801 A.D. Dome building occurred from 1781 to 1793. During that time, periodic, relatively small eruptions occurred.
Because Mt. Hood is a snow-clad volcano, activity results in melting of snow and mobilization of loose materials. Rainstorms could also mobilize loose debris in the area. Mt. Hood lahars have probably formed by both mechanisms.
Locality: Mt. Hood Volcano (looking east from the Jonsrud Viewpoint in the town of Sandy), northwestern Oregon, USA
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Info. at:
earth science, geology, geomorphology, landscape, altiplano, volcano, volcanoes, vulcanology, igneous, volcanic, stratovolcano, composite volcano, avalanche debris, parinacota, pomerape, lauca national park, national park, unesco, man and biosphere reserve, mab, chile, south america
(Aerial photo on public signage at Jonsrud Viewpoint in the town of Sandy, Oregon, USA.)
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Mt. Hood is a subduction zone stratovolcano in northwestern Oregon. It is part of the north-south trending Cascade Range of volcanoes from northern California to southwestern British Columbia. Other famous Cascade volcanoes include Mt. St. Helens, Mt. Rainier, Mt. Shasta, and Mt. Mazama (now Crater Lake Caldera).
Mt. Hood area volcanism started in the Middle Miocene, 8 to 10 million years ago, just after Columbia River Flood Basalt volcanism. Miocene and Pliocene andesites and basalts cap topographic ridges in the Mt. Hood area. During the Late Pliocene (sensu traditio), at 3 to 1.3 million years ago, the Sandy Glacier Volcano occupied the site of the current Mt. Hood. Sandy Glacier Volcano is now mostly buried by the modern Mt. Hood volcanic cone. Mt. Hood itself is less than 730,000 years old - all of its rocks have modern magnetic signatures. Lavas and other eruptive materials are high-silica andesites and low-silica dacites. 70% of the Mt. Hood cone consists of lava flows, while the remaining 30% is volcaniclcastic deposits. The modern cone is less than 300,000 years old. Near the summit of Mt. Hood are lava flows dating to younger than 200,000 years old.
Unlike nearby Mt. St. Helens, Mt. Hood is much older and has had little explosive activity. Most of Mt. Hood's volcanism has consisted of andesite lava flows and dome-building. Few explosive events have occurred through time here - few tephra deposits have a Mt. Hood source.
Mt. Hood rocks are often porphyritic two-pyroxene andesites, plus a little olivine. There's been little chemical variation in Mt. Hood lavas through time. Because of this, individual lava flows are difficult to date based on lithology - they're all the same. Much of Mt. Hood itself is hydrothermally-altered rocks.
Names are assigned to the various eruptive phases in Mt. Hood's history. The Polallie eruptive phase occurred from 12 to 25 thousand years ago. The Timberline eruptive phase occurred ~1500 years ago. The Old Maid eruptive phase occurred over 200 years ago, often dated to 1780-1801 A.D. Dome building occurred from 1781 to 1793. During that time, periodic, relatively small eruptions occurred.
Because Mt. Hood is a snow-clad volcano, activity results in melting of snow and mobilization of loose materials. Rainstorms could also mobilize loose debris in the area. Mt. Hood lahars have probably formed by both mechanisms.
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Info. at: