The Contenders: A Closer Look at Five High-Threat Volcanoes
The USGS “Very High Threat” list is a who’s who of American volcanoes, each dangerous for its own unique combination of geology and geography. Exploring five of these volcanoes reveals the diverse nature of volcanic risk across the country, from the lava-covered slopes of Hawaii to the ice-clad peaks of the Pacific Northwest and Alaska.
Kฤซlauea, Hawaii
Located on the Big Island of Hawaii, Kฤซlauea is one of the most active volcanoes on Earth. Its danger comes not from massive explosions, but from persistent, effusive eruptions of fluid basaltic lava. These lava flows, while often slow, can be voluminous and destructive, posing a direct threat to residential communities built on its flanks. The volcano’s location in the middle of the Pacific tectonic plate, over a geologic “hotspot,” is the source of its continuous activity.
The 2018 lower Puna eruption provided a stark, modern example of Kฤซlauea’s destructive power. Over a period of three months, fissures opened in the Leilani Estates subdivision, releasing massive flows of lava that ultimately destroyed over 700 homes, covered nearly 14 square miles of land, and reshaped the island’s coastline. The summit caldera also collapsed, triggering thousands of earthquakes. The event demonstrated the profound impact that lava flows can have on infrastructure, forcing the evacuation of thousands of residents and causing hundreds of millions of dollars in damages. The Hawaiian Volcano Observatory (HVO) closely monitored the event, providing critical, around-the-clock updates that enabled authorities to manage evacuations and prevent loss of life.
Mount St. Helens, Washington
Mount St. Helens seared itself into the American consciousness with its cataclysmic eruption on May 18, 1980. This event serves as a critical case study in modern volcanology and highlights the threat of explosive, gas-rich volcanoes. Located in the Cascade Range, Mount St. Helens is a product of the Cascadia subduction zone, where the Juan de Fuca oceanic plate dives beneath the North American continental plate, generating magma.
The 1980 eruption was preceded by two months of intense earthquake activity and ground deformation. The eruption began with a massive debris avalanche, triggered by a magnitude 5.1 earthquake, which “uncorked” the pressurized magma system within the volcano. This resulted in a powerful lateral blast that moved northward at over 300 miles per hour, leveling 230 square miles of forest. A vertical ash plume rose 15 miles into the atmosphere, and subsequent pyroclastic flows swept down the volcano’s slopes. The eruption caused 57 fatalities and remains the deadliest and most economically destructive volcanic event in U.S. history. Today, the Mount St. Helens Science and Learning Center and the USGS Cascades Volcano Observatory (CVO) use the volcano as a natural laboratory to improve monitoring and forecasting techniques for similar volcanoes worldwide.
Mount Rainier, Washington
Towering over the Seattle-Tacoma metropolitan area, Mount Rainier is often considered one of the most dangerous volcanoes in the United States. Its immense height (14,411 feet) and extensive glacial system make it a prime candidate for producing catastrophic lahars. While an eruption could generate pyroclastic flows and ashfall, the primary hazard for the more than 150,000 people living in its downstream river valleys is the threat of these volcanic mudflows.
Mount Rainier has the largest glacial system of any mountain in the contiguous U.S. An eruption could rapidly melt this ice and snow, generating lahars far larger than those seen at Mount St. Helens in 1980. Geologic evidence shows that massive lahars have swept down the Puyallup and Nisqually river valleys in the past, reaching all the way to Puget Sound. A future lahar could travel from the volcano to populated communities like Orting, Puyallup, and Sumner in less than an hour. This short timeframe makes robust early warning systems essential. In response, a network of Acoustic Flow Monitors (AFMs) has been installed along the major river channels. These sensors are designed to detect the unique ground vibrations of a lahar, automatically triggering sirens and public alerts to give residents a critical window of timeโpotentially 40 to 60 minutesโto evacuate to high ground.
Mount Hood, Oregon
The highest peak in Oregon, Mount Hood is a stunning backdrop to the city of Portland, located just 50 miles to the west. Like Mount Rainier, it is a glacier-clad stratovolcano in the Cascade Range with the potential for explosive eruptions. Its proximity to a major metropolitan area and vital transportation corridors, including the Columbia River, places it high on the threat list. Its last significant eruptive period occurred just before the arrival of Lewis and Clark in the early 1800s.
The primary hazards from Mount Hood are pyroclastic flows, ashfall, and lahars. A future eruption could send lahars down the Sandy, Zigzag, and White River valleys, threatening several small communities and recreational areas on its flanks. Ashfall could disrupt operations at Portland International Airport and impact air quality across the region. The volcano is also a source of important water resources and a hub for tourism and recreation, all of which would be severely affected by an eruption. The Cascades Volcano Observatory monitors Mount Hood with seismometers, GPS receivers, and gas sensors to provide the earliest possible warning of renewed activity, working closely with state and local emergency managers to develop coordinated response plans.
Redoubt Volcano, Alaska
Alaska is home to the majority of the nation’s active volcanoes, many of which are located along the remote Aleutian arc. Redoubt Volcano, situated 110 miles southwest of Anchorage, represents a critical threat not primarily to ground communities, but to global aviation. The skies over Alaska and the North Pacific are a major highway for international flights between North America and Asia, and a volcanic ash cloud from a volcano like Redoubt can pose a lethal threat to aircraft.
Redoubt has erupted five times in the modern era, most recently in 2009. Its 1989 eruption had a profound impact on the aviation industry. On December 15, 1989, a KLM Boeing 747 flew into the ash cloud from Redoubt’s eruption. All four engines failed as the abrasive ash melted and then resolidified into glass inside the turbines. The aircraft plummeted more than two miles in altitude before the crew was able to restart the engines and land safely in Anchorage. This harrowing incident was a wake-up call, leading to the establishment of the global Volcanic Ash Advisory Center (VAAC) system. The Alaska Volcano Observatory (AVO) now provides constant surveillance of Redoubt and other Alaskan volcanoes, issuing rapid alerts and aviation color codes to help pilots and air traffic controllers avoid dangerous ash clouds, protecting thousands of passengers daily.
