These 18 American volcanoes were classified in the category "very high threat"

According to the USGS, there are 161 active and potentially active volcanoes across the country, which rank them in five categories according to the risks they represent for people and infrastructure.

Eighteen volcanoes are in the first category of those considered "a very great threat". This includes Kilauea, considered one of the most active volcanoes in the world.

Kilauea began to erupt in May, causing more than 110 earthquakes and hundreds of evacuations.

Hawaii has six active volcanoes, but only five are on the new USGS list and only one – Mauna Loa – figures in the first category of threats.

Volcanic hazards

In categorizing volcanic threat levels, the USGS took into account "24 factors describing the risk potential of a volcano and the exposure of people and property to these risks (regardless of any action or attenuation action) ".

The list published this week, updated from a 2005 assessment, is not a prediction of the next volcano eruption, but "an indicator of the potential severity of impacts that may result from future eruptions on a given volcano", John Ewert, USGS volcanologist and chief author of the report, writes in the report.

The researchers examined the stand level of an area in relation to a known lava flow area and the incidence of volcanic ash on air transport and airports.

Eleven of the 18 "very high threat" volcanoes are in the states of Washington, Oregon and California, the report says. Five are in Alaska, where high and moderate threat categories dominate, with volcanoes near "large population centers", the report adds.

After Kilauea in Hawaii, the St. Helens and Rainier Mountains of Washington are ranked second and third on the list. The dreaded Alaskan volcano and Mount Shasta California rank among the top five.

The most threatening

The most threatening volcano for the public is Mount Rainier, told CNN Angie Diefenbach, geologist at the USGS, co-author of the assessment.

"About 300,000 people are in the danger zone downriver near Mount Rainier, and eruptions can be dangerous and take long distances," Diefenbach said.

Diefenbach said the list of dangers of volcanoes is not intended to scare the public, but rather to help researchers monitor volcanoes more closely and prepare for eventual eruptions.

The resulting report considers 39 volcanoes as a high threat; 49 moderate threat; 34 weak threat; and very weak threat. In the category of very high threats are the following 18: