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Shasta

Photo of this volcano
  • Country
  • Volcanic Region
  • Landform | Volc Type
  • Last Known Eruption
  • 41.409°N
  • 122.193°W

  • 4,317 m
    14,163 ft

  • 323010
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number


Most Recent Bulletin Report: June 1992 (BGVN 17:06) Citation IconCite this Report

No seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Date Lassen Shasta Medicine Lake Geysers
Codas (seconds) <= 10 > 10 <= 10 > 10 <= 10 > 10 <= 10 > 10
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Shasta report. The film record showed no earthquake activity beneath Shasta (~900 km NNW of the epicenter), although telemetry problems limited the ability to detect events below M 2. Of the six earthquakes in the 24 hours following the M 7.5 shock, two were large enough to be recorded by the RTP system. These were centered about 60 km SE of Shasta and about equidistant from Lassen (figure 1). Because the arrival times and S-P sequences of the other four events were similar to those of the two located shocks, it is likely that all had similar epicenters. Occasional M 2 earthquakes have previously occurred in this area, which includes several mapped N-trending normal faults with Quaternary movement. Three days after the M 7.5 earthquake, a M 2.0 shock occurred beneath Shasta's SE flank, followed by a M 2.7 event the next day. Both were centered at about 15 km depth, similar to most earthquakes beneath Shasta in the last decade.

Figure (see Caption) Figure 1. Seismic events in the Shasta/Medicine Lake area that were apparently triggered by the M 7.5 southern California earthquake of 28 June 1992 (circles) compared to 1978-90 seismicity in the region (crosses). Squares mark seismic stations. Courtesy of Stephen Walter.

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.

The Global Volcanism Program has no Weekly Reports available for Shasta.

Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

07/1978 (SEAN 03:07) Earthquake swarm; maximum M 4.2

08/1978 (SEAN 03:08) Earthquakes decline to few a day

09/1978 (SEAN 03:09) Daily seismcity declines; no evidence of volcanic activity

06/1992 (BGVN 17:06) No seismicity triggered by M 7.5 earthquake hundreds of kilometers away




Information is preliminary and subject to change. All times are local (unless otherwise noted)


July 1978 (SEAN 03:07) Citation IconCite this Report

Earthquake swarm; maximum M 4.2

An earthquake swarm in the vicinity of Mt. Shasta began at 0202 on 1 August. The first event, M 4.2, was followed by six M 3-4 events in the next 45 minutes. Between 35 and 40 shocks (M greater than or equal to 2) were recorded on 1 August. The number of events declined slightly the next day and only about ten had been recorded by midday on 3 August. About 20 of the total had M greater than or equal to 3. Permanent seismographs were too distant for precise hypocenter determinations, but USGS personnel were bringing portable seismographs into the area.

An ash eruption, probably from Shasta, was sighted from a ship off the California coast in 1786.

Information Contacts: R. Lester, USGS, Menlo Park, CA.


August 1978 (SEAN 03:08) Citation IconCite this Report

Earthquakes decline to few a day

The number of earthquakes declined to only a few events per day (M greater than or equal to 2) by 11 August. However, on 12 August a M 4.3-4.5 shock was followed by several similar events (approximately M 4), and others in the M 3.5-4 range occurred on the 13th. Activity then declined again; on 23 August only 13 events of M 2-2.5 were recorded, and by the end of August only about six events greater than M 2 were being recorded daily.

Epicenters have been located along about 2 km of a pre-existing N-S-trending fault zone 28 km E of the summit. Uncertain crustal velocities for the area have made depth determinations difficult, but all events have been shallow, probably less than 5 km, and some may have been less that 1 km deep. No migration of events has been observed. New tensional fissures have been found in the epicentral area, but were not growing as of late August. Leveling, microearthquake studies, and gravity profiles are planned.

Information Contacts: R. Sherburne, California Division of Mines & Geology; A. Walter, USGS, Menlo Park, CA.


September 1978 (SEAN 03:09) Citation IconCite this Report

Daily seismcity declines; no evidence of volcanic activity

Seismic activity E of Mt. Shasta had declined by late September to about six locatable events per day, most stronger than M 2. Hypocenters extended E from surface fissures 28 km E of Shasta, along a pre-existing N-S-trending fault zone. Focal depths were very shallow near the surface fissures, but increased to 4-6 km along an inclined seismic zone dipping 35-45° E. The events have not been migrating, nor has there been any evidence of volcanic activity associated with the swarm.

Further Reference. Bennett, J.H., et al., 1979, Stephens Pass earthquakes, Mount Shasta—August 1978; California Geology, February, 1979, p. 27-33.

Information Contacts: R. Sherburne, California Division of Mines & Geology.


June 1992 (BGVN 17:06) Citation IconCite this Report

No seismicity triggered by M 7.5 earthquake hundreds of kilometers away

Southern California's largest earthquake since 1952, M 7.5 on 28 June, appeared to trigger seismicity at several volcanic centers in California. It was centered roughly 200 km E of Los Angeles. In the following, David Hill describes post-earthquake activity at Long Valley caldera, and Stephen Walter discusses the USGS's seismic network, and the changes it detected at Lassen, Shasta, Medicine Lake, and the Geysers.

In recent years, the USGS northern California seismic network has relied upon Real-Time Processors (RTPs) to detect, record, and locate earthquakes. However, a film recorder (develocorder) collects data from 18 stations in volcanic areas, primarily to detect long-period earthquakes missed by RTPs. The film recorders proved useful in counting the post-M 7.5 earthquakes, most of which were too small to trigger the RTPs.

The film record was scanned for the 24 hours after the M 7.5 earthquake, noting the average coda duration for each identified event. Some events may have been missed because of seismogram saturation by the M 7.5 earthquake. Marked increases in microseismicity were observed at Lassen Peak, Medicine Lake caldera, and the Geysers (table 1). No earthquakes were observed at Shasta, but the lack of operating stations on the volcano limited the capability to observe small events.

Table 1. Number of earthquakes at northern California volcanic centers during 24-hour periods following major earthquakes on 25 April (40.37°N, 124.32°W; M 7.0) and 28 June (34.18°N, 116.47°W; M 7.5) 1992. Events with coda durations less than or equal to 10 seconds and greater than 10 seconds are tallied separately. Earthquakes were identified from film records of seismograms from nearby stations. Courtesy of Stephen Walter.

Date Lassen Shasta Medicine Lake Geysers
Codas (seconds) <= 10 > 10 <= 10 > 10 <= 10 > 10 <= 10 > 10
25 Apr 1992 0 0 0 1 0 0 7 2
28 Jun 1992 8 14 1 5 12 0 46 4

Film was also scanned for the 24 hours following the M 7.0 earthquake at 40.37°N, 124.32°W (near Cape Mendocino) on 25 April. Although smaller than the 28 June earthquake, its epicenter was only 20-25% as far from the volcanoes. Furthermore, both the 25 April main shock and a M 6.5 aftershock were felt at the volcanic centers, but no felt reports were received from these areas after the 28 June earthquake. Only the Geysers showed any possible triggered events after the 25 April shock. However, background seismicity at the Geysers is higher than at the other centers, and is influenced by fluid injection and withdrawal associated with intensive geothermal development.

Shasta report. The film record showed no earthquake activity beneath Shasta (~900 km NNW of the epicenter), although telemetry problems limited the ability to detect events below M 2. Of the six earthquakes in the 24 hours following the M 7.5 shock, two were large enough to be recorded by the RTP system. These were centered about 60 km SE of Shasta and about equidistant from Lassen (figure 1). Because the arrival times and S-P sequences of the other four events were similar to those of the two located shocks, it is likely that all had similar epicenters. Occasional M 2 earthquakes have previously occurred in this area, which includes several mapped N-trending normal faults with Quaternary movement. Three days after the M 7.5 earthquake, a M 2.0 shock occurred beneath Shasta's SE flank, followed by a M 2.7 event the next day. Both were centered at about 15 km depth, similar to most earthquakes beneath Shasta in the last decade.

Figure (see Caption) Figure 1. Seismic events in the Shasta/Medicine Lake area that were apparently triggered by the M 7.5 southern California earthquake of 28 June 1992 (circles) compared to 1978-90 seismicity in the region (crosses). Squares mark seismic stations. Courtesy of Stephen Walter.

Information Contacts: Stephen Walter and David Hill, MS 977, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 USA.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Eruptive History

There is data available for 22 confirmed Holocene eruptive periods.

[ 1786 ] Discredited Eruption

The original ships map inspected by William Miesse, along with reviews and analysis by US Geological and Smithsonian volcanologists, showed that the "smoke" reported during a 1786 voyage by La Perouse was due to a grass fire along the California coast (see summary by Leman, 2019). Fieldwork in 2019 found no evidence of an eruption from that time period.

1250 (?) Confirmed Eruption  

Episode 1 | Eruption
1250 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 4 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Blocks

1200 (?) Confirmed Eruption  

Episode 1 | Eruption
1200 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lahar or Mudflow

0850 (?) Confirmed Eruption  

Episode 1 | Eruption
0850 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 3 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Tephra

0150 (?) Confirmed Eruption  

Episode 1 | Eruption
0150 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 4 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Tephra
   - - - -    - - - - Lahar or Mudflow Uncertain

0050 (?) Confirmed Eruption VEI: 0

Episode 1 | Eruption
0050 (?) - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
0050
(?)
   - - - - VEI (Explosivity Index)

0150 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
0150 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 3 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Tephra

0550 BCE ± 500 years Confirmed Eruption  

Episode 1 | Eruption
0550 BCE ± 500 years - Unknown Evidence from Correlation: Tephrochronology

List of 6 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lava flow
   - - - -    - - - - Lava dome
   - - - -    - - - - Ash
   - - - -    - - - - Blocks

0650 BCE ± 800 years Confirmed Eruption  

Episode 1 | Eruption
0650 BCE ± 800 years - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 5 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Blocks
   - - - -    - - - - Lahar or Mudflow

0850 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
0850 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 3 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lahar or Mudflow

1150 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
1150 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lahar or Mudflow

2050 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
2050 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lahar or Mudflow

2550 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
2550 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lahar or Mudflow

3050 BCE ± 1000 years Confirmed Eruption VEI: 0

Episode 1 | Eruption
3050 BCE ± 1000 years - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
3050 BCE ± 1000 years    - - - - VEI (Explosivity Index)

4050 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
4050 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 5 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Blocks
   - - - -    - - - - Lahar or Mudflow

6050 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
6050 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 3 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow Uncertain
   - - - -    - - - - Lahar or Mudflow

6650 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
6650 BCE (?) - Unknown Evidence from Correlation: Tephrochronology

List of 5 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Blocks
   - - - -    - - - - Lahar or Mudflow

7250 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
7250 BCE (?) - Unknown Evidence from Correlation: Tephrochronology

List of 3 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lava flow
   - - - -    - - - - Pumice

7350 BCE (?) Confirmed Eruption VEI: 0

Episode 1 | Eruption Summit, north and west flanks
7350 BCE (?) - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1 at Summit, north and west flanks

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
7350 BCE
(?)
   - - - - VEI (Explosivity Index)

7420 BCE ± 300 years Confirmed Eruption  

Episode 1 | Eruption Shastina and Black Butte
7420 BCE ± 300 years - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 3 Events for Episode 1 at Shastina and Black Butte

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lava dome

7650 BCE ± 100 years Confirmed Eruption VEI: 4

Episode 1 | Eruption Summit, S flank (Red Banks), and Shastina
7650 BCE ± 100 years - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 7 Events for Episode 1 at Summit, S flank (Red Banks), and Shastina

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lava flow
   - - - -    - - - - Ash
   - - - -    - - - - Lapilli
   - - - -    - - - - Blocks
   - - - -    - - - - Pumice
7650 BCE ± 100 years    - - - - VEI (Explosivity Index)

7750 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
7750 BCE (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 6 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Blocks
   - - - -    - - - - Pumice
   - - - -    - - - - Lahar or Mudflow

8050 BCE (?) Confirmed Eruption  

Episode 1 | Eruption
8050 BCE (?) - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
Deformation History

There is no Deformation History data available for Shasta.

Emission History

There is no Emissions History data available for Shasta.

Photo Gallery

These hills below the north flank of Mount Shasta are hummocks resulting from the massive Shasta Valley debris avalanche deposit, which formed during a major volcanic flank collapse event in the Pleistocene. Individual hummocks, composed of remnants of the ancestral Shasta volcano, are up to 200 m high and some are more than 1 km long.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
Mount Shasta one of the largest volcanoes of the Cascade Range, is located in northern California at the southern end of the Cascades. It is seen here beyond the Little Glass Mountain obsidian flow from Medicine Lake volcano to the NE.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
Black Buttes is a group of overlapping lava domes on the lower western flank of Mount Shasta that formed during the early Holocene, around the same time as the formation of Shastina on the upper west flank. Block-and-ash flows accompanying dome growth traveled over 10 km S. The notches on the western flank (left) mark the tops of several individual domes.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
The extensively eroded Sargents Ridge (right of center), on the south side of Mount Shasta, is a remnant of the oldest of four major edifices that were constructed following the collapse of ancestral Mount Shasta. The Sargents Ridge cone formed during the Pleistocene, less than 250,000 years ago. Mount Misery was constructed less than 130,000 years ago and forms much of the upper part of the cone above the Sargents Ridge cone.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
Shastina forms the west flank of Mount Shasta with Whitney Glacier at its base. It is composed of overlapping lava flows and domes. Emplacement of the Shastina domes about 9,700-9,400 years ago was accompanied by pyroclastic flows and lava flows that traveled long distances down its flanks.

Photo by Bill Chadwick, 1981 (U.S. Geological Survey).
The foreground hills are part of the Shasta Valley debris avalanche deposit produced by one of the largest known Quaternary volcanic landslides. Roughly 46 km3 of an ancestral Mount Shasta collapsed about 350,000 year ago, producing a massive debris avalanche that swept some 50 km to the north, filling the broad Shasta Valley with hummocky debris.

Photo by Dave Wieprecht, 1995 (U.S. Geological Survey).
The prominent lava dome of Shastina, seen here on the right from the north, formed on the west flank of Shasta between about 9,700 and 9,400 years ago. The Shastina summit contains several overlapping domes. Hotlum cone to the left forms the main summit of Shasta and is likely younger than Shastina.

Photo by Dan Dzurisin, 1982 (U.S. Geological Survey).
Hotlum cone, seen here from the NW, forms the main summit of Mount Shasta and is one of the largest Cascade Range volcanoes. Hotlum is composed of several overlapping edifices and formed during the Holocene.

Photo by Bill Chadwick, 1981 (U.S. Geological Survey).
Mount Shasta in northern California, seen here from the SE, is one of the largest of the Cascades volcanoes and is constructed of at least four overlapping edifices. Hotlum cone (forming the summit), along with the Shastina and Black Buttes lava domes, were all constructed during the Holocene.

Photo by Lyn Topinka, 1984 (U.S. Geological Survey).
Shastina forms the largely snow-free ridge to the left of the summit of Shasta. During the growth of Shastina in the early Holocene, andesite lava flows traveled out to 14 km and pyroclastic flows swept down its flanks, covering much of the areas that are now the sites of the towns of Weed and Mt. Shasta.

Photo by Lyn Topinka, 1984 (U.S. Geological Survey).
A roadcut exposes the internal structure of the debris avalanche deposit that formed during collapse of Mount Shasta during the Pleistocene. This deposit contains large angular sections composed of rock and crushed matrix of similar material (like the light-gray area in this photo), in direct contact with other lithologies (brown) from other areas of the pre-collapse volcano. This is due to different sections mixing as the debris avalanche traveled across the landscape.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
Mount Shasta in northern California, the largest volcano of the Cascade Range, is a complex stratovolcano composed of at least four overlapping volcanoes. From the SW, Shasta's prominent west flank lava dome, Shastina, appears at the left. Both it and the summit Hotlum cone were formed during the Holocene. The only historical eruption of Shasta occurred in 1786 and was observed from off the coast of California by the French explorer La Perouse.

Copyrighted photo by Katia and Maurice Krafft, 1989.
The hilly topography in the foreground is part of the massive debris avalanche deposit produced by collapse of Mount Shasta (center horizon). The roughly 46 km3, rapidly-moving debris avalanche swept some 50 km N. The hummocky area represents relatively intact segments of the volcano that were carried within a more fluidized, mixed bulk of the avalanche. Individual hummocks range up to a few hundred meters in height and roughly 1 km in length.

Photo by Harry Glicken, 1982 (U.S. Geological Survey).
Hotlum cone forms the current Shasta summit and was constructed during the early Holocene.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
The Little Glass Mountain obsidian flow is seen from Little Mount Hoffman on the western rim of Medicine Lake caldera with Mount Shasta in the background. The flow was erupted on the SW flank of Medicine Lake volcano a little more than 950 years ago. The light-colored rounded peak in line with Mount Shasta is Pumice Stone Mountain, which is overlain by pumice from the Little Glass Mountain eruption. A series of smaller flows to the NE known as the Crater Glass Flows were erupted at about the same time.

Photo by Lee Siebert, 1981 (Smithsonian Institution).
The hilly topography in the foreground is part of the massive debris avalanche deposit produced by collapse of Mount Shasta (in the background) during the Pleistocene. These hummocks represent relatively intact blocks of the volcano that were carried within a more mobile landslide matrix (smaller blocks and grains, snow and ice, and anything entrained during transportation). The debris avalanche covered an area of about 675 km2, reaching at least 45 km NNE.

Photo by Harry Glicken, 1982 (U.S. Geological Survey).
Four overlapping dacite domes form the Black Buttes lava dome on the lower western flank of Mount Shasta. This view looks NW from the summit of Black Buttes, at the tops of two of the domes with the outskirts of the town of Weed below. Pyroclastic flows accompanying formation of Black Buttes extend 10 km S and 5 km N, and underlie currently populated areas.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
The forested hills and rolling pasture lands near the town of Montague are part of a massive debris avalanche deposit that originated from Mount Shasta during the Pleistocene. The hills consist of remnants of the former edifice of Mount Shasta that were transported relatively intact to this point, about 40 km NW of the volcano. The origin of the hills remained enigmatic until volcanologists noticed the resemblance to the avalanche deposit produced at Mount St. Helens in 1980.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
Massive Mount Shasta, the largest-volume volcano of the Cascade Range in northern California. It is seen here from the north, with Hotlum cone forming the summit and Shastina on the western flank. It is composed of at least four main edifices, of which the last two, Hotlum and Shastina, are of Holocene age.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
The broad partially forested lava flow extending across the center of the photo into Medicine Lake caldera is the Hoffman lava flow, which erupted about 1,170 years ago. The massive rhyolite lava flow and an adjacent smaller one were erupted from vents on the NE rim of the caldera. The larger of the two flows, seen here with the unvegetated Glass Mountain flow in the foreground, was erupted near the caldera rim and flowed both west into the caldera and down the east flank. Snow-capped Mount Shasta rises to the west.

Photo by Lee Siebert, 1998 (Smithsonian Institution).
An aerial view shows the Military Pass lava flow on NE side of Mount Shasta, the longest known lava flow from the volcano, erupted about 9,200 years ago. It originated near the summit of the Hotlum cone and reached about 9 km, with a thickness of about 150 m thick near its terminus. The flow overlies the Red Banks pumice and a broad fan of pyroclastic flow deposits that were formed around 9,700 years ago.

Photo by Dan Miller, 1980 (U.S. Geological Survey).
The Lava Park lava flow erupted about 9,300 years ago from a vent on the flank of Shastina, on the NW flank of Mount Shasta. The basaltic-andesite flow is about 6 km long and 110 m thick at the terminus. It overlies a wide apron of pyroclastic flow deposits emplaced about 9,700 years ago. The area shown is about 2 km wide and Highway 97 is seen near the bottom.

Photo by Dan Miller, 1980 (U.S. Geological Survey).
GVP Map Holdings

Maps are not currently available due to technical issues.

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included.

Smithsonian Sample Collections Database

The following 16 samples associated with this volcano can be found in the Smithsonian's NMNH Department of Mineral Sciences collections, and may be availble for research (contact the Rock and Ore Collections Manager). Catalog number links will open a window with more information.

Catalog Number Sample Description Lava Source Collection Date
NMNH 111123-1441 Hypersthene Andesite -- --
NMNH 111123-84 Hornblende Andesite -- --
NMNH 111123-84 Hornblende Andesite -- --
NMNH 111123-87 Hypersthene Andesite -- --
NMNH 111123-87 Hypersthene Andesite -- --
NMNH 112598 Andesite -- --
NMNH 116140-1 Andesite -- --
NMNH 2008 Andesite -- --
NMNH 2010 Hornblende Andesite -- --
NMNH 2014 Pumice -- --
NMNH 36977 Hornblende Andesite -- --
NMNH 36978 Hypersthene Andesite -- --
NMNH 36979 Hornblende Andesite -- --
NMNH 38362 Hornblende Andesite -- --
NMNH 38363 Hornblende Andesite -- --
NMNH 77152 Hornblende Andesite -- --
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