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Coordinates: 41°36′39″N 121°33′13″W / 41.610956028°N 121.553635458°W / 41.610956028; -121.553635458
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{{Short description|Shield volcano in northeastern California, United States}}
{{Infobox mountain
{{Infobox mountain
| name = Medicine Lake Volcano
| name = Medicine Lake Volcano
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| elevation_ft = 7921
| elevation_ft = 7921
| elevation_ref = {{NAVD88}}<ref name="ngs">{{cite ngs |id=MW0915 |designation=Hoffman |accessdate=2009-08-08}}</ref>
| elevation_ref = {{NAVD88}}<ref name="ngs">{{cite ngs |id=MW0915 |designation=Hoffman |accessdate=2009-08-08}}</ref>
| prominence =
| prominence_ft =
| prominence_ref=
⚫
| location = [[Siskiyou County, California]], [[United States|U.S.]]
| range = [[Cascade Range]]<ref name="LBNM_MLSV">
| range = [[Cascade Range]]<ref name="LBNM_MLSV">
{{cite web
{{cite web
Line 13: Line 14:
| publisher = [[National Park Service]]
| publisher = [[National Park Service]]
| url = http://www.nps.gov/archive/labe/content/RM_MedLakeVolcano.htm
| url = http://www.nps.gov/archive/labe/content/RM_MedLakeVolcano.htm
| accessdate = 2008-09-22}}</ref>
| access-date = 2008-09-22}}</ref>
⚫
| location = [[Siskiyou County, California]], U.S.
| lat_d = 41.610956028
| coordinates = {{coord|41.610956028|N|121.553635458|W|type:mountain_region:US-CA_scale:100000_source:NGS|format=dms|display=inline,title}}
| long_d = -121.553635458
| region = US-CA
| source = NGS
| coordinates_ref = <ref name="ngs"/>
| coordinates_ref = <ref name="ngs"/>
| topo = [[United States Geological Survey|USGS]] Medicine Lake
| topo = [[United States Geological Survey|USGS]] Medicine Lake
Line 23: Line 22:
| age = about 500,000 years<ref name="Donnelly_2007"/>
| age = about 500,000 years<ref name="Donnelly_2007"/>
| volcanic_arc = [[Cascade Volcanoes|Cascade Volcanic Arc]]<ref name="LBNM_MLSV"/>
| volcanic_arc = [[Cascade Volcanoes|Cascade Volcanic Arc]]<ref name="LBNM_MLSV"/>
| last_eruption = 1080 ± 25 years<ref name="gvp">{{cite gvp |vnum=1203-02- |name=Medicine Lake |accessdate=2008-08-25}}</ref>
| last_eruption = 1080 ± 25 years<ref name="gvp">{{cite gvp |vn=323020 |name=Medicine Lake |access-date=2008-08-25}}</ref>
| first_ascent =
| first_ascent =
| easiest_route =
| easiest_route =
}}
}}


{{Infobox body of water
{{Infobox_lake
| lake_name = Medicine Lake
| name = Medicine Lake
| image_lake = Medlake aerial USGS.gif
| image = Medlake aerial USGS.gif
| caption_lake = The lake with Mount Shasta in the background
| caption = The lake with Mount Shasta in the background
| alt = Medicine Lake with Mount Shasta in the background
| image_bathymetry = MedicineLakeBathymetricMeters20080926.png
| image_bathymetry = MedicineLakeBathymetricMeters20080926.png
| caption_bathymetry = Bathymetric Map
| alt_bathymetry = Bathymetric map of Medicine Lake
| caption_bathymetry = Bathymetric map
| coords = {{coord|41|34|54|N|121|35|56|W|region:US-CA_type:waterbody_source:gnis|name=Medicine Lake}}
| coords = {{coord|41|34|54|N|121|35|56|W|region:US-CA_type:waterbody_source:gnis|name=Medicine Lake}}
| location = [[California]]
| location = [[California]]
| type =
| type =
| inflow =
| inflow =
| pushpin_map=California
| pushpin_map_alt=Map of California
| outflow =
| outflow =
| catchment =
| catchment =
| basin_countries = United States
| basin_countries = United States
| length = {{convert|1|km|mi|1|disp=flip}}<ref name="Donnelly_2007"/>
| length = {{convert|1|km|mi|1|order=flip|abbr=on}}<ref name="Donnelly_2007"/>
| width = {{convert|2|km|mi|1|disp=flip}}<ref name="Donnelly_2007"/>
| width = {{convert|2|km|mi|1|order=flip|abbr=on}}<ref name="Donnelly_2007"/>
| area = {{convert|1.65|km2|sqmi|sigfig=2|disp=flip|abbr=on}}<ref name="Childs_2000"/>
| area = {{convert|1.65|km2|sqmi|sigfig=2|order=flip|abbr=on}}<ref name="Childs_2000"/>
| depth = {{convert|7.3|m|ft|1|disp=flip}}<ref name="Childs_2000"/>
| depth = {{convert|7.3|m|ft|1|order=flip|abbr=on}}<ref name="Childs_2000"/>
| max-depth = {{convert|46.4|m|ft|0|disp=flip}}<ref name="Childs_2000"/>
| max-depth = {{convert|46.4|m|ft|0|order=flip|abbr=on}}<ref name="Childs_2000"/>
| volume = {{convert|13400000|m3|cuft|disp=flip|abbr=on}}<ref name="Childs_2000"/>
| volume = {{convert|13400000|m3|cuft|order=flip|abbr=on}}<ref name="Childs_2000"/>
| residence_time =
| residence_time =
| shore = {{convert|6213|m|ft|0|disp=flip}}<ref name="Childs_2000"/>
| shore = {{convert|6213|m|ft|0|order=flip|abbr=on}}<ref name="Childs_2000"/>
| elevation =
| elevation =
| islands =
| islands =
| islands_category =
| islands_category =
| cities =
| cities =
| reference = <ref name="Donnelly_2007">{{cite journal
| reference = <ref name="Donnelly_2007">{{cite report
| author = Julie M. Donnelly-Nolan
| author = Julie M. Donnelly-Nolan
| coauthors = Manuel Nathenson, Duane E. Champion, David W. Ramsey, Jacob B. Lowenstern, and John W. Ewert
|author2=Manuel Nathenson |author3=Duane E. Champion |author4=David W. Ramsey |author5=Jacob B. Lowenstern |author6=John W. Ewert
| title = Volcano Hazards Assessment for Medicine Lake Volcano, Northern California - Scientific Investigations Report 2007–5174-A
| title = Volcano Hazards Assessment for Medicine Lake Volcano, Northern California – Scientific Investigations Report 2007–5174-A
| publisher = [[United States Geological Survey]]
| publisher = United States Geological Survey
| year = 2007
| year = 2007
| url = http://pubs.usgs.gov/sir/2007/5174/a/sir2007-5174a_text.pdf
| url = http://pubs.usgs.gov/sir/2007/5174/a/sir2007-5174a_text.pdf
⚫
| access-date = 2008-09-25}}</ref><ref name="Childs_2000">{{cite report
| format = [[PDF]]
⚫
| accessdate = 2008-09-25}}</ref><ref name="Childs_2000">{{cite journal
| author = Jonathan R. Childs
| author = Jonathan R. Childs
| coauthors = Jacob B. Lowenstern, R. Lawrence Phillips, Patrick Hart, James J. Rytuba, John A. Barron, Scott W. Starratt, and Sarah Spaulding
|author2=Jacob B. Lowenstern |author3=R. Lawrence Phillips |author4=Patrick Hart |author5=James J. Rytuba |author6=John A. Barron |author7=Scott W. Starratt |author8=Sarah Spaulding
| title = Bathymetric, geophysical and geologic sample data from Medicine Lake, Siskiyou County, northern California - Open File Report OF 00-043
| title = Bathymetric, geophysical and geologic sample data from Medicine Lake, Siskiyou County, northern California – Open File Report OF 00-043
| version = Version 2.0
| version = Version 2.0
| publisher = [[United States Geological Survey]]
| publisher = United States Geological Survey
| year = 2000
| year = 2000
| url = http://purl.fdlp.gov/GPO/gpo35896
| url = https://purl.fdlp.gov/GPO/gpo35896
| accessdate = 2008-09-25}}</ref>
| access-date = 2008-09-25}}</ref>
}}
}}
[[File:MedicineLkHighlands09272017-50.tif|250px|thumb|Medicine Lake Volcano, California, September 27, 2017. [[Sentinel-2]] true-color [[satellite image]], scale 1:50,000.]]


'''Medicine Lake Volcano''' is a large [[shield volcano]] in northeastern [[California]] about {{convert|50|km|mi|sigfig=1|disp=flip}} northeast of [[Mount Shasta]]. The [[volcano]] is located in a zone of east-west crustal extension east of the main axis of the [[Cascade Volcanoes|Cascade Volcanic Arc]] and the [[Cascade Range]]. The {{convert|1|km|mi|1|disp=flip|adj=on}} thick shield is {{convert|35|km|mi|0|disp=flip}} from east to west and {{convert|45|to|50|km|mi|0|disp=flip}} from north to south, and covers more than {{convert|2000|km2|sqmi|sigfig=2|disp=flip}}. The underlying rock has downwarped by {{convert|0.5|km|mi|1|disp=flip}} under the center of the volcano. The volcano is primarily composed of [[basalt]] and [[basaltic andesite]] lava flows, and has a {{convert|7|by|12|km|mi|1||disp=flip|adj=on}} [[caldera]] at the center.
'''Medicine Lake Volcano''' is a large [[shield volcano]] in northeastern [[California]] about {{convert|50|km|mi|sigfig=1|order=flip|abbr=on}} northeast of [[Mount Shasta]]. The [[volcano]] is located in a zone of east–west crustal extension east of the main axis of the [[Cascade Volcanoes|Cascade Volcanic Arc]] and the [[Cascade Range]]. The {{convert|1|km|mi|1|order=flip|adj=on|abbr=on}} thick shield is {{convert|35|km|mi|0|order=flip|abbr=on}} from east to west and {{convert|45|to|50|km|mi|0|order=flip|abbr=on}} from north to south, and covers more than {{convert|2000|km2|sqmi|sigfig=2|order=flip|abbr=on}}. The underlying rock has downwarped by {{convert|0.5|km|mi|1|order=flip|abbr=on}} under the center of the volcano. The volcano is primarily composed of [[basalt]] and [[basaltic andesite]] lava flows, and has a {{convert|7|by|12|km|mi|1||order=flip|adj=on|abbr=on}} [[caldera]] at the center.


The Medicine Lake shield rises about {{convert|1200|m|ft|sigfig=2|disp=flip}} above the [[Modoc Plateau]] to an elevation of {{convert|2376|m|ft|0|disp=flip}}. [[Lava]]s from Medicine Lake Volcano are estimated to be at least {{convert|600|km3|cumi|sigfig=2|disp=flip}} 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.
The Medicine Lake shield rises about {{convert|1200|m|ft|sigfig=2|order=flip|abbr=on}} above the [[Modoc Plateau]] to an elevation of {{convert|2376|m|ft|0|order=flip|abbr=on}}. [[Lava]]s from Medicine Lake Volcano are estimated to be at least {{convert|600|km3|cumi|sigfig=2|order=flip|abbr=on}} 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.
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==
==Caldera==
Medicine Lake is in the caldera of the volcano, which measures {{convert|7|by|12|km|mi|1|disp=flip}}. The caldera may have formed by collapse after a large volume of [[andesite]] was erupted from vents along the caldera rim. The distribution of late [[Pleistocene]] vents, mostly concentrated along the rim, suggests that ring faults already existed when most of the andesite erupted. No single large eruption has been related to caldera formation. The only eruption recognized to have produced [[Volcanic ash|ash]] flow [[tuff]] occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. Later conclusions were that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly mafic lava beginning early in the history of the volcano (perhaps in a manner similar to the formation of [[Kilauea]] caldera in [[Hawaii]]). Several small differentiated magma bodies may have been fed by and interspersed among a plexus of [[dike (geology)|dikes]] and [[Sill (geology)|sill]]s. 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.
Medicine Lake is in the caldera of the volcano, which measures {{convert|7|by|12|km|mi|1|order=flip|abbr=on}}. The caldera may have formed by collapse after a large volume of [[andesite]] was erupted from vents along the caldera rim. The distribution of late [[Pleistocene]] vents, mostly concentrated along the rim, suggests that ring faults already existed when most of the andesite erupted. No single large eruption has been related to caldera formation. The only eruption recognized to have produced [[Volcanic ash|ash]] flow [[tuff]] occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. Later conclusions were that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly [[mafic]] lava beginning early in the history of the volcano (perhaps in a manner similar to the formation of [[Kilauea]] caldera in [[Hawaii]]). Several small differentiated magma bodies may have been fed by and interspersed among a network of [[dike (geology)|dikes]] and [[Sill (geology)|sill]]s. 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==
==Eruptive history==


===Early history===
===Early history===
Medicine Lake Volcano began to grow about one million years ago in [[Pleistocene]] time, following the eruption of a large volume of tholeiitic high-[[alumina]] basalt. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Although [[mafic]] lavas predominate on the volcano's flanks, all lava compositions from basalt to [[rhyolite]] have erupted during Pleistocene time. The lower flanks consist of mostly basaltic and some andesitic lavas. Basalt is mostly absent at higher elevation, where andesite dominates and rhyolite and small volumes of dacite are present. During the past 11,000 years, eruptive activity at Medicine Lake Volcano has been episodic. Eight eruptions produced about {{convert|5.3|km3|cumi|1|disp=flip}} of basaltic lava during a time interval of a few hundred years about 10,500 years ago. That eruptive episode was followed by a hiatus that ended with a small andesitic eruption about 4,300 years ago. During the most recent eruptive episode between 3000 and 900 years ago, eight eruptions produced approximately {{convert|2.5|km3|cumi|1|disp=flip}} of lava ranging in composition from basalt to rhyolite. Late Holocene lava compositions include basalt and andesite, but [[silica|silicic]] lavas dominate.
Medicine Lake Volcano began to grow about one million years ago in [[Pleistocene]] time, following the eruption of a large volume of tholeiitic high-[[alumina]] basalt. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Although [[mafic]] lavas predominate on the volcano's flanks, all lava compositions from basalt to [[rhyolite]] have erupted during Pleistocene time. The lower flanks consist of mostly basaltic and some andesitic lavas. Basalt is mostly absent at higher elevation, where andesite dominates and rhyolite and small volumes of dacite are present. During the past 11,000 years, eruptive activity at Medicine Lake Volcano has been episodic. Eight eruptions produced about {{convert|5.3|km3|cumi|1|order=flip|abbr=on}} of basaltic lava during a time interval of a few hundred years about 10,500 years ago. That eruptive episode was followed by a hiatus that ended with a small andesitic eruption about 4,300 years ago. During the most recent eruptive episode between 3000 and 900 years ago, eight eruptions produced approximately {{convert|2.5|km3|cumi|1|order=flip|abbr=on}} of lava ranging in composition from basalt to rhyolite. Late Holocene lava compositions include basalt and andesite, but [[silica|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 North East to North West.
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 ===
[[Image:Glass Mountain.jpg|thumb|250px|right|Glass Mountain from Medicine Lake caldera rim. USGS photo by Julie Donnelly-Nolan.]]
[[File:Glass Mountain.jpg|thumb|250px|right|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. No field evidence has been found to substantiate a report of an eruption in 1910.{{Citation needed|date=December 2007}}
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.<ref>{{cite journal
| title = The Lassen Report: No. 14
| journal = The Volcano Letter
| last1 = Fitch
| first1 = R. H.
| year = 1928
| page = 1
| volume = 161
}}</ref><ref>{{cite journal |last=Macdonald |first=Gordon A. |date=1966 |title=Geology of the Cascade Range and Modoc Plateau |url=https://archive.org/details/northecalifornia00bailrich |journal=Geology of Northern California |publisher=United States Geological Survey |volume=190 |pages=65–95 |access-date=July 27, 2015}}</ref> No field evidence has been found to substantiate the 1910 eruption.<ref>{{cite book
| title = Volcanoes of North America: United States and Canada
| year = 1992
| page = 212
| publisher = Cambridge University Press
| editor1-last = Wood
| editor1-first = Charles A
| editor2-last= Kienle
| editor2-first = Jurgen
| url = https://books.google.com/books?id=eyDRib-FJh4C&pg=PA212
| isbn = 9780521438117
}}</ref>


Glass Mountain consists of a spectacular, nearly [[tree]]less, steep-sided rhyolite and dacite [[obsidian]] flow that erupted just outside the eastern caldera rim and flowed down the steep eastern flank of Medicine Lake Volcano. Ten additional small domes of Glass Mountain rhyolite and rhyodacite lava lie on a N25degreesW trend to the north and one to the south. The age of Glass Mountain and its preceding pumice deposits has been a matter of discussion for some time. A [[radiocarbon dating]] age of 885±40 years before present (1990) was obtained on a dead [[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 1050 years before present (1990) by the Little Glass Mountain and [[Lassen Peak]] data.
Glass Mountain consists of a spectacular, nearly [[tree]]less, steep-sided rhyolite and dacite [[obsidian]] flow that erupted just outside the eastern caldera rim and flowed down the steep eastern flank of Medicine Lake Volcano. Ten additional small domes of Glass Mountain rhyolite and rhyodacite lava lie on a N25degreesW trend to the north and one to the south. The age of Glass Mountain and its preceding pumice deposits has been a matter of discussion for some time. A [[radiocarbon dating]] age of 885±40 years before present (1990) was obtained on a dead [[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==
==See also==
Line 102: Line 124:


{{refbegin}}
{{refbegin}}
{{refend}}
* Adapted from [http://vulcan.wr.usgs.gov/Volcanoes/Cascades/volcanoes_cascade_range.html#medicine_lake USGS text] assumed to be in the public domain.
* Adapted from [http://vulcan.wr.usgs.gov/Volcanoes/Cascades/volcanoes_cascade_range.html#medicine_lake USGS text] assumed to be in the public domain.
* {{cite journal
* {{cite journal
| last = Donnelly-Nolan
| last = Donnelly-Nolan | first = J.M.
| first = J.M.
| year = 1990
| year = 1990
| url = http://vulcan.wr.usgs.gov/Volcanoes/MedicineLake/Publications/GeoMedLake/geo_medlake.pdf
| url = http://vulcan.wr.usgs.gov/Volcanoes/MedicineLake/Publications/GeoMedLake/geo_medlake.pdf
| title = Geology of Medicine Lake Volcano, Northern California, Cascade Range
| title = Geology of Medicine Lake Volcano, Northern California, Cascade Range
| journal = TRANSACTIONS
| journal = Transactions
| publisher = Geothermal Resources Council
| publisher = Geothermal Resources Council
| volume = 14, Part II
| volume = 14 Part II <!-- CS1 long volume value -->
| pages = 1395–1396 }}
| pages = 1395–1396 }}
{{refend}}
{{refend}}
Line 121: Line 141:
| title = Medicine Lake Vicinity, California, Lava Beds National Monument
| title = Medicine Lake Vicinity, California, Lava Beds National Monument
| publisher = Cascades Volcano Observatory [[United States Geological Survey|USGS]]
| publisher = Cascades Volcano Observatory [[United States Geological Survey|USGS]]
| accessdate = 2010-05-22 }}
| access-date = 2010-05-22 }}
* {{cite web
* {{cite web
| url = http://www.sacredland.org/losing-sacred-ground/
| url = http://www.sacredland.org/losing-sacred-ground/
| title = Losing Sacred Ground
| title = Losing Sacred Ground
| publisher = Sacred Land Film Project
| publisher = Sacred Land Film Project
| accessdate = 2010-05-22 }}
| access-date = 2010-05-22
| archive-url = https://web.archive.org/web/20110718183126/http://www.sacredland.org/losing-sacred-ground/
| archive-date = 2011-07-18
| url-status = dead
}}


{{Cascade volcanoes}}
{{Cascade volcanoes}}


{{authority control}}
⚫
[[Category:Religious places of the indigenous peoples of North America]]

⚫
[[Category:Shield volcanoes]]
[[Category:Cascade Volcanoes]]
[[Category:Volcanoes of Siskiyou County, California]]
[[Category:Volcanoes of Siskiyou County, California]]
[[Category:Sacred mountains]]
[[Category:Lava Beds National Monument]]
⚫
[[Category:Modoc National Forest]]
⚫
[[Category:Modoc Plateau]]
⚫
[[Category:Religious places of the Indigenous peoples of North America]]
[[Category:Sacred mountains of the Americas]]
⚫
[[Category:Shield volcanoes of the United States]]
[[Category:Subduction volcanoes]]
[[Category:Subduction volcanoes]]
[[Category:Cascade Volcanoes]]
[[Category:Calderas of California]]
[[Category:Volcanic calderas of the United States]]
[[Category:Volcanic crater lakes]]
⚫
[[Category:Crater lakes]]
⚫
[[Category:VEI-3 volcanoes]]
[[Category:Lakes of Siskiyou County, California]]
[[Category:Lakes of Siskiyou County, California]]
[[Category:Lava Beds National Monument]]
[[Category:Lakes of Northern California]]
[[Category:Modoc National Forest]]
[[Category:Lakes of California]]
[[Category:Volcanoes of California]]

[[Category:Polygenetic shield volcanoes]]
[[fr:Medicine Lake]]

Latest revision as of 01:37, 29 November 2024

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
Map
LocationSiskiyou County, California, U.S.
Parent rangeCascade Range[2]
Topo mapUSGS Medicine Lake
Geology
Rock ageabout 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.
Medicine Lake Volcano, California, September 27, 2017. Sentinel-2 true-color 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

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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 andesite was erupted from vents along the caldera rim. The distribution of late Pleistocene vents, mostly concentrated along the rim, suggests that ring faults already existed when most of the andesite erupted. No single large eruption has been related to caldera formation. The only eruption recognized to have produced ash flow tuff occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. Later conclusions were that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly mafic lava beginning early in the history of the volcano (perhaps in a manner similar to the formation 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

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Early history

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Medicine Lake Volcano began to grow about one million years ago in Pleistocene time, following the eruption of a large volume of tholeiitic high-alumina basalt. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Although mafic lavas predominate on the volcano's flanks, all lava compositions from basalt to rhyolite have erupted during Pleistocene time. The lower flanks consist of mostly basaltic and some andesitic lavas. Basalt is mostly absent at higher elevation, where andesite dominates and rhyolite and small volumes of dacite are present. During the past 11,000 years, eruptive activity at Medicine Lake Volcano has been episodic. Eight eruptions produced about 1.3 cu mi (5.3 km3) of basaltic lava during a time interval of a few hundred years about 10,500 years ago. That eruptive episode was followed by a hiatus that ended with a small andesitic eruption about 4,300 years ago. During the most recent eruptive episode between 3000 and 900 years ago, eight eruptions produced approximately 0.6 cu mi (2.5 km3) of lava ranging in composition from basalt to rhyolite. Late Holocene lava compositions include basalt and andesite, but 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

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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 treeless, steep-sided rhyolite and dacite obsidian flow that erupted just outside the eastern caldera rim and flowed down the steep eastern flank of Medicine Lake Volcano. Ten additional small domes of Glass Mountain rhyolite and rhyodacite lava lie on a N25degreesW trend to the north and one to the south. The age of Glass Mountain and its preceding pumice deposits has been a matter of discussion for some time. A radiocarbon dating age of 885±40 years before present (1990) was obtained on a dead 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

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References

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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. United States Geological Survey: 65–95. Retrieved July 27, 2015.
  8. ^ Wood, Charles A; Kienle, Jurgen, eds. (1992). Volcanoes of North America: United States and Canada. Cambridge University Press. p. 212. ISBN 9780521438117.
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