The United States has 169 active volcanoes — 55 of which are designated as serious threats by the United States Geological Survey's Volcano Hazards Program.
Of these, 18 are "Very High Threats"— volcanoes that, were they to erupt, could disrupt air travel and threaten people's lives.
A caveat: this is not a ranking of the volcanoes by their danger level.
As Wendy Stovall, a geologist with USGS, told Business Insider in an e-mail:
There are many volcanoes that are threatening due to factors such as tectonic setting, population density, eruption frequency, and potential to erupt again. The variations in these factors make each of the ... 'high threat' volcanoes uniquely dangerous.
Since they pose such substantial threats, we figured we should get to know them a little better. So, here are the 18 most dangerous volcanoes in the US.
Mount Akutan, in the Alaskan Aleutian Island chain, last erupted in 1992, releasing ash and steam for nearly three months.
In May of 2005, Augustine Volcano in Alaska began experiencing a number of "microearthquakes," which built to explosive eruptions of ash that reached nine kilometers above sea level.
Makushin Volcano, located in the Aleutian island chain of Alaska, has erupted 34 times in the last 250 years— most recently in 1995.
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