Mount McLoughlin
Encyclopedia
Mount McLoughlin is a steep-sided lava
cone
built on top of a shield volcano
in the Cascade Range
of southern Oregon
and within the Sky Lakes Wilderness area
. It is one of the volcanic peaks in the Cascade Volcanic Arc
. The mountain is north of Mount Shasta
, south of Crater Lake
, and west of Upper Klamath Lake
. It was named around 1838 after John McLoughlin
, a Chief Factor for the Hudson's Bay Company
.
Mount McLoughlin has been known by a number of different names over the years, including Mount Pitt (after the Pit River
), Big Butte, M'laiksini Yaina (Klamath Indians), Malsi (Takelma Indians), Mount Shasty (although this name was applied to Mount Shasta
to the south by the 1841 Wilkes Expedition), and Snowy Butte.
The Pacific Crest Trail
skirts the eastern and northern sides and also accesses the only trail to the summit. On a clear day, the Sky Lakes Wilderness area
, Crater Lake
, Rogue Valley
, and Mount Shasta are visible from the summit.
.
The 3 cubic miles (13 km³) volcano went through three or four stages of development and stopped growing some time before the most recent period of glaciation about 25,000 years ago.
The first known stage of the volcano's growth was explosive and built a large cinder cone from a single vent that may have reached the unusual height of 3000 foot and may account for one third of McLoughlin's present interior. A steep-sided pre-existing shield volcano
may exist within the cinder cone, thus explaining its extreme height. Some lava
is associated with this stage but is confined to the lower parts of the cinder cone. A second cone-building stage was characterized by large andesite
lava flows that poured out of a summit crater and in time buried the cinder cone. The third stage of development consisted of floods of blocky andesite lava erupting from below the summit and more fluid lavas erupting from basal fissures, mostly confined to the south slope. North Squaw Tip
and South Squaw Tip
on McLoughlin's west flank now mark the site of the two major blocky flow vents. There were two smaller vents as well. The entire third stage is thought to have happened in the Holocene
period, after the last ice age
, due to a general lack of weathering
and fresh appearance of the solidified lava.
During the last ice age, a large ice cap
buried most of the High Cascades, with Mount McLoughlin marking the southern terminus of this structure. The ice cap was 200 foot thick where it touched the mountain. A large ice-age glacier
on the northeast side of the volcano severely eroded that part of the mountain, creating an asymmetrical cone. A cirque
glacier occupied part of the depression until early in the 20th century. The volcano's crest is located south of the central vent and its crater has long since been eroded away along with about 500 foot of its former height.
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...
cone
Volcanic cone
Volcanic cones are among the simplest volcanic formations. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption...
built on top of a 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...
in 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...
of southern 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...
and within the Sky Lakes Wilderness area
Sky Lakes Wilderness
The Sky Lakes Wilderness is a wilderness area located in the Rogue River-Siskiyou and Winema National Forests in the southern Cascade Range of Oregon, U.S.. It comprises . of the area are located in the Rogue River-Siskiyou National Forest, and located in the Winema National Forest...
. It is one of the volcanic peaks in 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 ...
. The mountain is north of 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...
, south of 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 west of Upper Klamath Lake
Upper Klamath Lake
Upper Klamath Lake is a large, shallow freshwater lake east of the Cascade Range in south central Oregon in the United States. The largest freshwater body in Oregon, it is approximately 20 mi long and 8 mi wide and extends northwest from the city of Klamath Falls...
. It was named around 1838 after John McLoughlin
John McLoughlin
Dr. John McLoughlin, baptized Jean-Baptiste McLoughlin, was the Chief Factor of the Columbia Fur District of the Hudson's Bay Company at Fort Vancouver. He was later known as the "Father of Oregon" for his role in assisting the American cause in the Oregon Country in the Pacific Northwest...
, a Chief Factor for the Hudson's Bay Company
Hudson's Bay Company
The Hudson's Bay Company , abbreviated HBC, or "The Bay" is the oldest commercial corporation in North America and one of the oldest in the world. A fur trading business for much of its existence, today Hudson's Bay Company owns and operates retail stores throughout Canada...
.
Mount McLoughlin has been known by a number of different names over the years, including Mount Pitt (after the Pit River
Pit River
The Pit River is a major river draining from northeastern California into the state's Central Valley. The Pit, the Klamath and the Columbia are the only three rivers in the U.S...
), Big Butte, M'laiksini Yaina (Klamath Indians), Malsi (Takelma Indians), Mount Shasty (although this name was applied to 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...
to the south by the 1841 Wilkes Expedition), and Snowy Butte.
The Pacific Crest Trail
Pacific Crest Trail
The Pacific Crest Trail is a long-distance mountain hiking and equestrian trail on the Western Seaboard of the United States. The southern terminus is at the California border with Mexico...
skirts the eastern and northern sides and also accesses the only trail to the summit. On a clear day, the Sky Lakes Wilderness area
Sky Lakes Wilderness
The Sky Lakes Wilderness is a wilderness area located in the Rogue River-Siskiyou and Winema National Forests in the southern Cascade Range of Oregon, U.S.. It comprises . of the area are located in the Rogue River-Siskiyou National Forest, and located in the Winema National Forest...
, 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...
, Rogue Valley
Rogue Valley
The Rogue Valley is a farming and timber-producing region in southwestern Oregon in the United States. Located along the middle Rogue River and its tributaries in Josephine and Jackson counties, the valley forms the cultural and economic heart of Southern Oregon near the California border. The...
, and Mount Shasta are visible from the summit.
Geology
Except for a short monograph written by Arthur B. Emmons in 1886, little was known about Mount McLoughlin's geology until the 1970s. Much of what is known today comes from LeRoy Maynard of the Center for Volcanology at University of OregonUniversity of Oregon
-Colleges and schools:The University of Oregon is organized into eight schools and colleges—six professional schools and colleges, an Arts and Sciences College and an Honors College.- School of Architecture and Allied Arts :...
.
The 3 cubic miles (13 km³) volcano went through three or four stages of development and stopped growing some time before the most recent period of glaciation about 25,000 years ago.
The first known stage of the volcano's growth was explosive and built a large cinder cone from a single vent that may have reached the unusual height of 3000 foot and may account for one third of McLoughlin's present interior. A steep-sided pre-existing 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...
may exist within the cinder cone, thus explaining its extreme height. Some 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...
is associated with this stage but is confined to the lower parts of the cinder cone. A second cone-building stage was characterized by large andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
lava flows that poured out of a summit crater and in time buried the cinder cone. The third stage of development consisted of floods of blocky andesite lava erupting from below the summit and more fluid lavas erupting from basal fissures, mostly confined to the south slope. North Squaw Tip
and South Squaw Tip
on McLoughlin's west flank now mark the site of the two major blocky flow vents. There were two smaller vents as well. The entire third stage is thought to have happened in the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
period, after the last 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...
, due to a general lack of weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
and fresh appearance of the solidified lava.
During the last ice age, a large ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....
buried most of the High Cascades, with Mount McLoughlin marking the southern terminus of this structure. The ice cap was 200 foot thick where it touched the mountain. A large ice-age 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...
on the northeast side of the volcano severely eroded that part of the mountain, creating an asymmetrical cone. A cirque
Cirque (landform)
thumb|250 px|Two cirques with semi-permanent snowpatches in [[Abisko National Park]], [[Sweden]].A cirque or corrie is an amphitheatre-like valley head, formed at the head of a valley glacier by erosion...
glacier occupied part of the depression until early in the 20th century. The volcano's crest is located south of the central vent and its crater has long since been eroded away along with about 500 foot of its former height.
See also
- Cascade VolcanoesCascade VolcanoesThe 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 ...
- Geology of the Pacific NorthwestGeology of the Pacific NorthwestThe geology of the Pacific Northwest refers to the study of the composition , structure, physical properties and the processes that shape the Pacific Northwest region of the United States and Canada...
- Volcanic Legacy Scenic BywayVolcanic Legacy Scenic BywayThe Volcanic Legacy Scenic Byway is an All-American Road in the U.S. states of California and Oregon. It is roughly 500 miles long and travels through the Cascade Range past numerous volcanoes. It is composed of two separate National Scenic Byways, the Volcanic Legacy Scenic Byway - Oregon and...