Medicine Lake Volcano

Coordinates: 41°36′39″N 121°33′13″W / 41.610956028°N 121.553635458°W / 41.610956028; -121.553635458
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Medicine Lake Volcano
Medicine Lake volcano as seen from Lava Beds National Monument
Highest point
Elevation7,921 ft (2,414 m) NAVD 88[1]
Coordinates41°36′39″N 121°33′13″W / 41.610956028°N 121.553635458°W / 41.610956028; -121.553635458[1]
Geography
LocationSiskiyou County, California, U.S.
Parent rangeCascade Range[2]
Topo mapUSGS Medicine Lake
Geology
Age of rockabout 500,000 years[3]
Mountain typeShield volcano
Volcanic arcCascade Volcanic Arc[2]
Last eruption1080 ± 25 years[4]
Medicine Lake
Medicine Lake with Mount Shasta in the background
The lake with Mount Shasta in the background
Map of California
Map of California
Medicine Lake
Bathymetric map of Medicine Lake
Bathymetric map
LocationCalifornia
Coordinates41°34′54″N 121°35′56″W / 41.58167°N 121.59889°W / 41.58167; -121.59889 (Medicine Lake)
Basin countriesUnited States
Max. length0.6 mi (1 km)[3]
Max. width1.2 mi (2 km)[3]
Surface area0.64 sq mi (1.65 km2)[5]
Average depth24.0 ft (7.3 m)[5]
Max. depth152 ft (46.4 m)[5]
Water volume470,000,000 cu ft (13,400,000 m3)[5]
Shore length120,384 ft (6,213 m)[5]
References[3][5]
1 Shore length is not a well-defined measure.
satellite image
, scale 1:50,000.

Medicine Lake Volcano is a large shield volcano in northeastern California about 30 mi (50 km) northeast of Mount Shasta. The volcano is located in a zone of east-west crustal extension east of the main axis of the Cascade Volcanic Arc and the Cascade Range. The 0.6 mi (1 km) thick shield is 22 mi (35 km) from east to west and 28 to 31 mi (45 to 50 km) from north to south, and covers more than 770 sq mi (2,000 km2). The underlying rock has downwarped by 0.3 mi (0.5 km) under the center of the volcano. The volcano is primarily composed of basalt and basaltic andesite lava flows, and has a 4.3 by 7.5 mi (7 by 12 km) caldera at the center.

The Medicine Lake shield rises about 3,900 ft (1,200 m) above the Modoc Plateau to an elevation of 7,795 ft (2,376 m). Lavas from Medicine Lake Volcano are estimated to be at least 140 cu mi (600 km3) in volume, making Medicine Lake the largest volcano by volume in the Cascade Range (Newberry Volcano in Oregon has the second largest volume). Lava Beds National Monument lies on the northeast flank of the volcano.

Medicine Lake Volcano has been active for 500,000 years. The eruptions were gentle rather than explosive like Mount St. Helens, coating the volcano's sides with flow after flow of basaltic lava. Medicine Lake is part of the old caldera, a bowl-shaped depression in the mountain. It is believed that the Medicine Lake volcano is unique, having many small magma chambers rather than one large one.

Caldera

Medicine Lake is in the caldera of the volcano, which measures 4.3 by 7.5 mi (7 by 12 km). The caldera may have formed by collapse after a large volume of

Kilauea caldera in Hawaii). Several small differentiated magma bodies may have been fed by and interspersed among a network of dikes and sills. Late Holocene
andesitic to rhyolitic lavas were derived by fractionation, assimilation, and mixing from high alumina basalt parental magma. The small lake from which Medicine Lake volcano derives its name lies within the central caldera.

Eruptive history

Early history

Medicine Lake Volcano began to grow about one million years ago in

silicic
lavas dominate.

Eruptive activity during Holocene time has included numerous rhyolite and dacite lava flows erupted at high elevations inside and outside the caldera; cinder cones and associated lava flows of basalt and basaltic andesite have resulted from eruptions at vents on the flanks of the shield. Most vents are aligned along zones of crustal weakness that trend northeast to northwest.

Glass Mountain

Glass Mountain from Medicine Lake caldera rim. USGS photo by Julie Donnelly-Nolan.

The most recent eruption occurred around 1,000 years ago when rhyolite and dacite erupted at Glass Mountain and associated vents near the caldera's eastern rim. Fitch cites reports that a light ash fall that occurred in 1910 may have come from a small eruption at Glass Mountain.[6][7] No field evidence has been found to substantiate the 1910 eruption.[8]

Glass Mountain consists of a spectacular, nearly

incense-cedar tree without limbs or bark that is preserved in the edge of one of the distal tongues of the flow. The dated material consisted of a piece of exterior wood containing about 30 annual growth rings. This age may be too old, because some of the outside of the tree is missing. The tephra deposits that precede the flow and domes may be somewhat older but are constrained to be less than about 1,050 years before present (1990) by the Little Glass Mountain and Lassen Peak
data.

See also

References

Wikimedia Commons has media related to Medicine Lake Volcano.
  1. ^ a b "Hoffman". NGS Data Sheet. National Geodetic Survey, National Oceanic and Atmospheric Administration, United States Department of Commerce. Retrieved 2009-08-08.
  2. ^ a b "Medicine Lake Shield Volcano: The Sleeping Giant". Lava Beds National Monument. National Park Service. Retrieved 2008-09-22.
  3. ^ a b c d Julie M. Donnelly-Nolan; Manuel Nathenson; Duane E. Champion; David W. Ramsey; Jacob B. Lowenstern; John W. Ewert (2007). Volcano Hazards Assessment for Medicine Lake Volcano, Northern California - Scientific Investigations Report 2007–5174-A (PDF) (Report). United States Geological Survey. Retrieved 2008-09-25.
  4. ^ "Medicine Lake". Global Volcanism Program. Smithsonian Institution. Retrieved 2008-08-25.
  5. ^ a b c d e f Jonathan R. Childs; Jacob B. Lowenstern; R. Lawrence Phillips; Patrick Hart; James J. Rytuba; John A. Barron; Scott W. Starratt; Sarah Spaulding (2000). Bathymetric, geophysical and geologic sample data from Medicine Lake, Siskiyou County, northern California - Open File Report OF 00-043 (Report). Version 2.0. United States Geological Survey. Retrieved 2008-09-25.
  6. ^ Fitch, R. H. (1928). "The Lassen Report: No. 14". The Volcano Letter. 161: 1.
  7. ^ Macdonald, Gordon A. (1966). "Geology of the Cascade Range and Modoc Plateau". Geology of Northern California. 190. USGS: 65–95. Retrieved July 27, 2015.
  8. ISBN 9780521438117
    .

External links

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