Why is it important to monitor volcanoes?

The United States and its territories contain 169 geologically active volcanoes, of which 54 volcanoes are a high threat or very high threat to public safety. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more people and property are at risk from volcanic activity.

Volcanic eruptions are one of Earth's most dramatic and violent agents of change. Not only can powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano, but tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet's climate temporarily. Eruptions often force people living near volcanoes to abandon their land and homes, sometimes forever. Farther away, cities, crops, industrial plants, transportation systems, airplanes, and electrical grids can still be damaged by tephra, ash, lahars, and flooding.

Fortunately, volcanoes exhibit precursory unrest that, when detected and analyzed in time, allows eruptions to be anticipated and communities at risk to be forewarned. The warning time preceding volcanic events typically allows sufficient time for affected communities to implement response plans and mitigation measures.


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How were the Hawai’i lava-flow hazard zones determined?

The hazard zones for Hawai'i Island are based on: The locations of probable eruption sites (which are based on past eruption sites) The likely paths of lava flows erupted from those sites (based on topography and the paths of previous lava flows) The frequency of lava flow inundation of an area over the past several thousand years. The hazard...

How dangerous is Mount Rainier?

Although Mount Rainier has not produced a significant eruption in the past 500 years, it is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes , active hydrothermal system , and extensive glacier mantle. Mount Rainier has 26 glaciers containing more than five times as much snow and ice as...

How far did the ash from Mount St. Helens travel?

The May 18, 1980 eruptive column at Mount St. Helens fluctuated in height through the day, but the eruption subsided by late afternoon. By early May 19th, the eruption had stopped. By that time the ash cloud had spread to the central United States. Two days later, even though the ash cloud had become more diffuse, fine ash was detected by systems...

Lava sampling: Why do we do it?

Hot lava samples provide important information about what's going on in a volcano's magma chambers. We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis, therefore, provides the means not only to determine the crystallization history of lava but also to establish the temperature at...

How are volcanic gases measured?

Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode. An instrument that detects carbon dioxide can be installed on a volcano and configured to send data continuously via radio to an observatory...

How can we tell when a volcano will erupt?

Most volcanoes provide warnings before an eruption. Magmatic eruptions involve the rise of magma toward the surface, which normally generates detectable earthquakes. It can also deform the ground surface and cause anomalous heat flow or changes in the temperature and chemistry of the groundwater and spring waters. Steam-blast eruptions, however,...

Is it dangerous to work on volcanoes? What precautions do scientists take?

Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern, because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train...

How often do Alaskan volcanoes erupt?

Alaskan volcanoes have produced one or two eruptions per year since 1900. At least 20 catastrophic caldera -forming eruptions have occurred in the past 10,000 years; the awesome eruption of 1912 at Novarupta in the Katmai National Monument is the most recent. Scientists are particularly concerned about the volcanoes whose eruptions can affect the...

What was the largest volcanic eruption in the 20th century?

The World's largest eruption of the 20th century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6th. This volume is equivalent to 230 years of eruption at Kilauea (Hawaii) or about 30 times the volume erupted by Mount St. Helens (Washington...
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Date published: May 6, 2019

The National Volcano Early Warning System (NVEWS) will help USGS better monitor nation’s most dangerous volcanoes

In September 2004, USGS scientists detected sudden, but unmistakable, signs that Mount St. Helens was waking up. Volcano monitors had picked up the occurrence of hundreds of small earthquakes and other signals that the volcano’s crater floor had begun to rise. Within a week, several eruptions blasted clouds of ash into the atmosphere, and soon after, a new lava dome emerged in the crater.

Date published: December 19, 2018

Which U.S. volcanoes pose a threat?

USGS Volcanic Threat Assessment updates the 2005 rankings.

Date published: May 16, 2017


Which sounds more dangerous, lava or mud? The answer may surprise you...

Date published: May 1, 2017

May is Volcano Preparedness Month in Washington State

May is Volcano Preparedness Month in Washington, providing residents an opportunity to become more familiar with volcano hazards in their communities and learn about steps they can take to reduce potential impacts.

Date published: August 2, 2016

30 Years Saving Lives from Volcanoes

There are approximately 1,550 potentially active volcanoes around the world. VDAP works to reduce loss of life and property, limit economic impact and prevent volcanic crises from becoming disasters.

Date published: February 1, 2016

EarthWord – Nuée Ardente

A nuée ardente is a turbulent, fast moving cloud of hot gas and ash erupted from a volcano. 

Date published: September 3, 2015

Media Advisory: Remobilized 100-Year-Old Volcanic Ash: Is It a Health Hazard?

Two community events about monitoring old volcanic ash resuspended by high winds are scheduled next week in the City of Kodiak and in Larsen Bay, Alaska.

Attribution: Alaska
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Map of Aleutian Island chain with locations of volcanoes and commercial air traffic routes indicated
March 3, 2017

Air traffic over active volcanoes in the Aleutians

North Pacific and Russian Far East air routes (gray lines) pass over or near more than a hundred potentially active volcanoes (red triangles). Aircraft flying along these routes, some of the busiest in the world, carry more than 50,000 passengers and millions of dollars of cargo each day to and from Asia, North America, and Europe. In the North Pacific region, several

Mt. Pinatubo Monitoring Equipment Installation
November 9, 2016

Mount Pinatubo Monitoring Equipment Installation

Staff from VDAP and the Philippine Institute of Volcanology and Seismology install electronic tiltmeters to monitor inflation of the ground at Mt. Pinatubo in the Phillipines in June 1991. Photograph credit: USGS/VDAP

March 22, 2016

Monitoring Volcanoes Using ASTER Satellite Imagery

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor is one of five sensors on board NASA's Terra satellite. ASTER data and imagery are crucial tools for monitoring volcanoes for any clues of imminent eruptions, for studying volcanoes during an eruption, and for analyzing impacts after an eruption. Scientists use ASTER imagery to study the

video thumbnail: Volcano Hazards
July 30, 2012

Volcano Hazards

The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.

Video Sections:

  • Volcanoes: Monitoring Volcanoes
May 9, 2012

Volcano Web Shorts 6: Societal Impacts of Volcanism

USGS geologist, Angie Diefenbach, describes how she uses GIS, (Geographic Information Systems) software to study volcanic eruptions and their impacts on society.

May 9, 2012

Volcano Web Shorts 5 - Volcanic Ash Impacts

Volcanic ash is geographically the most widespread of all volcanic hazards. USGS geologist Larry Mastin describes how volcanic ash can disrupt lives many thousands of miles from an erupting volcano. The development of ash cloud models and ash cloud disruption to air traffic is highlighted.

May 9, 2012

Volcano Web Shorts 4 - Instruments

USGS technologist Rick LaHusen describes how the development and deployment of instruments plays a crucial role in mitigating volcanic hazards.

May 9, 2012

Volcano Web Shorts 3: Seismology

USGS volcano seismologist, Seth Moran, describes how seismology and seismic networks are used to mitigate volcanic hazards.

May 9, 2012

Volcano Web Shorts 1: Photogrammetry

Photogrammetry is the science of making precise measurements by the use of photography. USGS geologist Angie Diefenbach describes how she uses a digital camera and computer software to understand the growth rate of lava domes during a volcanic eruption.

May 9, 2012

Volcano Web Shorts 2: Debris Flows

Debris flows are hazardous flows of rock, sediment and water that surge down mountain slopes and into adjacent valleys. Hydrologist Richard Iverson describes the nature of debris-flow research and explains how debris flow experiments are conducted at the USGS Debris Flow Flume, west of Eugene, Oregon. Spectacular debris flow footage, recorded by Franck Lavigne of the

December 8, 2011

PubTalk 12/2011 — Tracking Ongoing Kilauea Eruptions

--fissures...fountains...and flows

by Matthew Patrick, USGS, Hawaiian Volcano Observatory


  • Spectacular Kilauea eruptions have produced a summit lava lake, roiling for several years, and a flank eruption recently sending lava flows downslope to threaten residential areas
  • How do USGS scientists monitor and track