There are 65 volcanoes in the United States and its territories that scientists consider active, including Mount St. Helens, in Washington State. Of those volcanoes, 12 are on alert, which means they are on heightened watch for eruptive activity, and two are erupting right now or expected to erupt shortly.

Volcanic activity is constantly monitored by the U.S. Geological Survey, which is responsible for alerting the population and airlines, of potential volcanic activities and issuing a warning if there is an impending volcanic eruption, said USGS seismologist Seth Moran.

“For a remote volcano, airlines need to know that a volcano might erupt so they are prepared to change their route to avoid the ash,” USGS Volcano Hazards Program coordinator John Eichelberger told Life’s Little Mysteries.

“For a volcano near population centers, people may need to take precautions such as having dust masks, staying out of a danger zone or in extreme cases they may need to evacuate,” said Eichelberger. Below are four of the seven most dangerous volcanic areas in the U.S., according to the USGS Volcano Hazards Program’s Volcano Alerts watch list. Click on the button below to see all seven of the most dangerous U.S. volcanic regions.

See List of Active Volcanoes at Live Science

Kilauea Volcano

Kilauea is one of the world’s most active volcanoes. It is a shield-type volcano that makes up the southeastern side of the Big Island of Hawaii. The volcano rises 4,190 feet (1,227 meters) above sea level and is about 14 percent of the land area of the Big Island. The summit caldera contains a lava lake known as Halema`uma`u that is said to be the home of the Hawaiian volcano goddess, Pele.

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Pagan Volcano

Pagan Island is part of the Mariana Islands archipelago, which lie to the south of Japan and just west of the Mariana Trench, where the deepest spot on Earth is found. The island is one of the largest and one of the most active volcanoes in the archipelago, according to the Smithsonian’s Global Volcanism Program.

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Anatahan Volcano

When Anatahan first erupted in 2003, the island’s 23 residents were already long gone – they had been evacuated during seismic activity in 1990. Anatahan’s most recent eruption lasted from 2007 to 2008, and the volcano remains on green-level alert.

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Yellowstone Volcano

Situated in Yellowstone National Park in Wyoming, the Yellowstone caldera’s floor moved upward almost 3 inches (7.6 cm) each year between 2004 and 2008. Since 2009, the uplift has significantly slowed, but the movement of the caldera’s floor is considered to be unpredictable. During the month of April 2010, the Yellowstone region experienced 117 minor earthquakes, which are common volcanic activities.

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