How many active volcanoes are in the US?

MikeMaster99

The perhaps surprising answer from the USGS to this question is 169! http://volcanoes.usgs.gov/about/faq/faqhazards.php Mar 30 12, 8:46 PM

queproblema

The figure is misleading. Most of those volcanoes are in Alaska and Hawaii. Also, vulcanologists don't have a consensus on what the definition of "active" is. "Mount St. Helens is one of more than 65 active or potentially active volcanoes in the continental United States, Alaska, and Hawaii." http://egsc.usgs.gov/isb/pubs/teachers-packets/volcanoes/lesson6/lesson6.html#US "Alaska contains over 130 volcanoes and volcanic fields which have been active within the last two million years. . . . Of these volcanoes, about 90 have been active within the last 10,000 years (and might be expected to erupt again), and more than 50 have been active within historical time (since about 1760, for Alaska). . . The volcanoes in Alaska make up well over three-quarters of U.S. volcanoes that have erupted in the last two hundred years." http://www.avo.alaska.edu/volcanoes/about.php I can see three out my window--one dead, one "active" but last erupted over 300,000 years ago, the other active, last erupting (gently) ten years ago. No problem. Mar 31 12, 12:45 PM

MikeMaster99

I'm sorry, I'm now a little confused. I gave the answer the USGS provides for all the US which obviously includes Alaska and Hawaii. The original question did not specify the contiguous 48, otherwise as you correctly point out, the number would be much lower than the 169 I cited. Mar 31 12, 10:37 PM

queproblema

Sorry, Mike; the figure 169 is misleading, but so was my response. Or at least garbled. Because you said, "The perhaps surprising answer," I imagined you were envisioning volcanoes dotting the 48 states, so I pointed out most are in Alaska or Hawaii so the answer wouldn't seem so surprising. Then I cited a much lower number from the same source you turned to--the U.S. Geological Survey. To answer this question properly, we first need to define "active" for the purposes of this question only, since experts disagree. I really don't like pasting in great walls of text, but here goes: When is a volcano considered active? Surprisingly, there is no consensus among volcanologists on how to define an active volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of activity. Given the long lifespan of such volcanoes, they are very active. By our lifespans, however, they are not. Complicating the definition are volcanoes that become restless but do not actually erupt. Are these volcanoes active? Active volcano Scientists usually consider a volcano active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It's important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in Hawai`i, little more than 200 years. Dormant volcano Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Extinct volcano Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. For example, since calderas have lifespans sometimes measured in millions of years, a caldera that hasn't produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. Yellowstone caldera in Yellowstone National Park is at least 2 million years old and hasn't erupted for 70,000 years, yet scientists do not consider Yellowstone as extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system, and rapid rates of ground uplift, many scientists consider it to be a very active volcano! http://volcanoes.usgs.gov/images/pglossary/volcano.php And here's an informative map: http://volcanoes.usgs.gov/ Apr 01 12, 8:12 PM