Long Valley Caldera example

1. Volcano name:

Long Valley Caldera

2. Location (closest town, country):

Mammoth Lakes, California is the closest town to the caldera because it lies within it! The caldera is 20 km south of Mono Lake on the eastern side of the Sierra Nevada, in southern California.

3. Geographic setting: where is your volcano? Is it on an island or in a mountain range? What does it look like? Is it tall or flat? How big is it? Include as many details as you can find. Draw a picture of your volcano.

The Long Valley Caldera is an oval-shaped depression, 20 miles long and 10 miles wide. A resurgent dome of magma is active beneath the middle of the caldera and provides heat for hotsprings. Ash deposits, fault scarps, cinder cones and dried lava surround the caldera. The caldera is part of the Mono-Inyo volcano chain.

4. Describe and draw a picture of how your volcano erupts.

The caldera formed around 760 thousand years ago when an eruption spewed out 150 CUBIC MILES of magma in the form of ash and pyroclastic materials. After emitting all of this material the roof of the magma chamber collapsed 2 to 3 km. There might have also been mudflows at this time. This eruption produced the Bishop Tuff which is a thick ash deposited found throughout the region. Many different kinds of eruptions have occurred in the area: firey cinder eruptions, basaltic lava flows and pyroclastic eruptions.

5. What volcano type is your volcano [shield, strato, etc.]? Refer to your responses above and the volcano chart from Activity 1.

This volcano is a caldera complex

6. When did your volcano last erupt? What evidence is used: photos, eyewitness accounts, historical documents, rock deposits?

The volcano last erupted around 550 to 650 years ago. There has been activity in the area for the last 3 million years. Geologists know about all these eruptions from rock deposits in the area. There has been earthquake activity in the region since 1980 and the dome within the caldera has since uplifted 25 cm. In addition to this uplift, gas emissions, thermal springs and earthquakes tell geologists that the magma underneath the volcano is still very very active! Careful monitoring has detected the recent activity over the past 20 years.

7. Was the eruption hazardous to people? What happened? Describe the destruction.

If people were in the area 550 to 650 years ago it would have been dangerous. Ash could bury and suffocate people. Gas could kill many of the trees as it does today. There is evidence of ground cracking, lava flows, craters, pumice, ash fall and obsidian deposits from this eruption - not a place any living critter would want to be.

8. If the volcano erupts again, what are the possible hazards? Does it pose a threat now?

The future hazards depend on the magnitude of the eruption. The earthquake data tell geologists that the threat of volcanic eruption is present - they just don't know when it will happen and how big it will be. The chance of an eruption is less than 1% for any given year. The USGS has established a monitoring system in the event to prevent disaster. Massive earthquakes, ash flows and pyroclastic flows could destroy property, close roads and communication lines. Gas emissions could directly hurt or kill any living organisms.

9. What are 2 cool facts about your volcano?

1. The water in the hot springs in and near the caldera boils! Due to the high altitude (higher air pressure) the water boils at 93 C, instead of 100 C (boiling temperature at sea level).
2. Tephra deposits from a massive eruption in Long Valley could reach as far as San Francisco

10. What are 2 questions you still have about your volcano?

1. Is there any archaeological evidence of people living in the area at the time of the eruption 600 years ago? What happened to them? How did they respond?
2. Has the USGS response team ever issued an ORANGE (eruption likely) warning to the nearby towns? How did they respond? What happened?

11. Which mountains in Tucson do you think are volcanoes?

They'd be in the Tucson Mountains, if anywhere.

12. List all of the sources [web pages and books/magazines] that you used to get the information on your volcano.

General information USGS site: http://lvo.wr.usgs.gov/index.html