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By: David P. Hill, Roy A. Bailey, and Alan S. Ryall

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1 By: David P. Hill, Roy A. Bailey, and Alan S. Ryall
Active Tectonic and Magmatic Processes Beneath Long Valley Caldera, Eastern California: An Overview By: David P. Hill, Roy A. Bailey, and Alan S. Ryall Presented by: Kristin Hepper


3 Long Valley Caldera at a Glance…

4 Long Valley Caldera 150 years of earthquake activity M 5-6 level
The last 10,000-20,000 years

5 Most Recent Eruptions Most recent = 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

6 Inyo Craters

7 The 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

8 Recent 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

9 Next 3 years- This raised concerns
Moderate earthquake swarms and rapid fire sequences Continued inflation This raised concerns Large earthquake Renewed volcanic activity in the area

10 History 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

11 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

12 The Bishop Tuff Covered 1500km2
Thickness=1500m within the 17 by 32 km Long Valley Caldera The caldera formed by collapse

13 The Bishop Tuff

14 Youngest Eruptions Inyo/Mono craters chain
Erupted roughly every 500 years for the last years N trending dike 8-12km long, 200 m from the surface

15 Future eruptions will be from the younger and more frequently active Mono/Inyo crater chain

16 The magma chamber Seismic measurements
Resurgent dome Seismic measurements Roof=6-7km beneath resurgent dome Volume of present magma chamber is between 500 and 1000km3


18 Closer to recent business
Began in fall of 1978 Inflation of resurgent dome Cumulative uplift of resurgent dome=50cm

19 The cause of the earthquakes
NE-SW extension Between mid 1979 and ~1984, resurgent dome increased its volume by km3

20 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 °C ( °F) water


22 The Geothermal System-Mammoth geothermal
The Geothermal System-Mammoth geothermal power facility (produces 40Mw of electrical energy)

23 Comparison with other Calderas
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

24 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

25 Keep in mind The Inyo/Mono craters erupted 500-600 years ago
Erupted ~2km3 of material Each vented ejected ~0.2km3 of material Produced ash falls and pyroclastic flows that extended 6-9km from the vents Sierra Nevada Mono Lake Active Fumaroles

26 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

27 Mt. St. Helens

28 Mt. St. Helens in all its glory…
May 18, 1980

29 Conclusions Long lived silicic magma chamber beneath Long Valley
A smaller magma chamber beneath Inyo/Mono Craters Eruptions may be preceded by multiple episodes of unrest

30 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 years ago…and it erupts every 500 years…is it due again?

31 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

32 View from on top Mammoth Mountain
Horseshoe Lake Area where trees were killed recently by high levels of carbon dioxide gas in the soil

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