By: David P. Hill, Roy A. Bailey, and Alan S. Ryall
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Transcript of By: David P. Hill, Roy A. Bailey, and Alan S. Ryall
Active Tectonic and Magmatic Active Tectonic and Magmatic Processes Beneath Long Processes Beneath Long Valley Caldera, Eastern Valley Caldera, Eastern California: An OverviewCalifornia: An Overview
By: David P. Hill, Roy A. Bailey, and Alan S. Ryall
Presented by: Kristin Hepper
Long Valley Caldera at a Glance…
Long Valley CalderaLong Valley Caldera
150 years of earthquake activity
M 5-6 level
The last 10,000-20,000 years
Most Recent EruptionsMost Recent Eruptions
Most recent = 500-600 years ago along Inyo/Mono craters chain
These are the most recent caldera forming eruptions within the boundaries of the US– Except for the Cascades
Inyo Craters
The Long Valley RegionThe Long Valley Region
Is the boundary between the Sierra Nevada and Basin and Range Provinces
Contemporary encroachment of Basin and Range into the Sierra Nevada
Recent HistoryRecent History October 1978- M 5.7
earthquake
1 ½ years later- swarmlike sequence of M6 earthquakes within 48hrs of each other
This was the onset of the inflation of the resurgent dome
Next 3 years-– Moderate earthquake swarms and rapid fire
sequences– Continued inflation
This raised concerns– Large earthquake– Renewed volcanic activity in the area
History of Volcanic ActivityHistory of Volcanic Activity
Volcanism began ~3.2mya
Began with displacement of the Sierran frontal fault scarp
There were basaltic eruptions extending over a 4,000km2 area
Volcanic Activity cont…Volcanic Activity cont…
The area existed in a potentially explosive state for 400,000 years
0.73mya a 600km3 of magma was ejected from the magma chamber– Now called the Bishop Tuff
The Bishop TuffThe Bishop Tuff
Covered 1500km2
Thickness=1500m within the 17 by 32 km Long Valley Caldera
The caldera formed by collapse
The Bishop Tuff
Youngest EruptionsYoungest Eruptions
Inyo/Mono craters chain
Erupted roughly every 500 years for the last 2-3000 years
N trending dike 8-12km long, 200 m from the surface
Future eruptions will be from the younger and more frequently active Mono/Inyo crater chain
The magma chamberThe magma chamber Seismic measurements
Roof=6-7km beneath resurgent dome
Volume of present magma chamber is between 500 and 1000km3
Resurgent dome
Closer to recent businessCloser to recent business
Began in fall of 1978
Inflation of resurgent dome
Cumulative uplift of resurgent dome=50cm
The cause of the earthquakesThe cause of the earthquakes
NE-SW extension
Between mid 1979 and ~1984, resurgent dome increased its volume by 0.1-0.2km3
Geothermal…Geothermal…Intermediate between the giant Yellowstone
and the smaller Valles calderas
Shallow convective hydrothermal system
There are active thermal springs and fumaroles at Casa Diablo and Hot creek– Fed by 100-170°C (212-338 °F) water
The Geothermal System-Mammoth geothermal power facility (produces 40Mw of electrical energy)
Comparison with other Comparison with other CalderasCalderas
200 calderas around the world have shown unrest
During a “typical” year, 14 calderas show some signs of unrest– Ground deformation in 3– Eruptions from 6-7
Other calderas out there…Other calderas out there…
Long Valley is one of the 4 major calderas in the world
Includes: Rabaul in New Guinea, the Phlegraean Fields in Italy, Long Valley in California, and Yellowstone in Whyoming
Keep in mindKeep in mindThe Inyo/Mono craters erupted 500-600
years agoErupted ~2km3 of material
– Each vented ejected ~0.2km3 of material Produced ash falls and pyroclastic flows that
extended 6-9km from the vents
Mono Lake
Sierra Nevada
Active Fumaroles
Earlier eruptions- ejected ~0.2km3 of magma (Long Valley)
Comparable to Mt. St. Helens which erupted on May 18, 1980
Caldera forming eruption in Long Valley
Was 700,000 years ago
Produced 600km3 of magma
Mt. St. HelensMt. St. Helens
Mt. St. Helens in all its glory…Mt. St. Helens in all its glory…
May 18, 1980
ConclusionsConclusionsLong lived silicic magma chamber beneath
Long Valley
A smaller magma chamber beneath Inyo/Mono Craters
Eruptions may be preceded by multiple episodes of unrest
This can be separated by decades of quiet
Most likely, the Inyo/Mono Crater chain will produce the next large eruption
Inyo/Mono last erupted 500-600 years ago…and it erupts every 500 years…is it due again?
An eruption from either system though will be preceded by accelerated levels of unrest
There should be ample warning
A large earthquake in the area however, could set the whole system off
View from on top Mammoth Mountain
Horseshoe Lake
Area where trees were killed recently by high levels of carbon dioxide gas in the soil