Volcanic Activity Risk in the US: How FEMA Scores It and How to Prepare

Written by Dvir · Data: FEMA National Risk Index v1.20 · Updated July 19, 2026

The United States is one of the most volcanically active countries on Earth — about 170 potentially active volcanoes, with Alaska, Hawaii, and the Cascade Range hosting the dangerous majority. Yet volcanic activity is among the National Risk Index’s smallest hazards by expected dollars: roughly $60 million in national expected annual loss across 283 counties (hazard code VLCN). The gap between “small annual number” and “Mount St. Helens” is the whole story of this hazard: decades of quiet punctuated by events that reshape landscapes — 1980’s eruption killed 57 people and remains the deadliest in US history, and Kilauea’s 2018 eruption destroyed more than 700 homes.

What counts as volcanic activity risk

The NRI’s volcanic hazard covers eruptions and their products, which differ wildly in reach and lethality. Pyroclastic flows — avalanches of superheated gas and rock at 100+ mph — destroy everything in their path but stay within miles of the vent. Lahars (volcanic mudflows) are the sleeper threat: eruptions or even heavy rain can melt snowpack and send concrete-like slurries down river valleys for tens of miles — this is Mount Rainier’s signature hazard, with entire towns (Orting, Puyallup) built on old lahar deposits. Lava flows destroy property but rarely kill (Hawaii’s problem). Ashfall is the wide-area hazard: abrasive, conductive glass powder that grounds aviation, shorts electronics, collapses roofs when wet, and can fall hundreds of miles downwind. Alaska’s frequent eruptions matter nationally mostly through ash in trans-Pacific air routes.

How the NRI measures it

FEMA combines each county’s exposure inside volcanic hazard zones, annualized eruption frequency from USGS records, and historic loss ratios into an Expected Annual Loss scored 0–100 against all counties. With events this episodic, the near-term frequencies are tiny — the top-ranked counties record an event every 50–100 years in the data — so exposure to well-mapped hazard zones does most of the work.

Where the risk concentrates

Hawaii County, HI (the Big Island) leads the nation — score 100, ~$26M expected annual loss, with Kilauea among the world’s most active volcanoes and lava-zone maps that directly govern insurance and property values. The Cascades fill the rest of the top five: Cowlitz County, WA (downstream of Mount St. Helens), Pierce County, WA (Tacoma — in Mount Rainier’s lahar shadow, the highest-stakes volcanic exposure in America), Skagit County, WA (Mount Baker and Glacier Peak), and Alaska’s Aleutians West. Oregon’s Hood River and Deschutes counties, California’s Shasta and Long Valley regions, and Anchorage (ash from Cook Inlet volcanoes) carry the remaining meaningful risk. Yellowstone, for the record, shows no signs of doing anything on a human timescale.

How to read your county’s score

Volcanic risk is the most precisely mapped hazard in the index — USGS publishes hazard-zone maps for every dangerous US volcano, and your risk is almost entirely a function of which zone you occupy. The questions: Are you in a lahar pathway (valley floors downstream of Rainier, St. Helens, Hood, Shasta)? In Hawaii, which lava zone (1–9) is the parcel in — zones 1–2 face genuine flow risk and near-uninsurable premiums? Downwind of an Alaska or Cascade volcano for ashfall? Each zone has a different playbook, and outside the zones, a high county score may barely apply to you.

What actually reduces the risk

  • Know your zone and your route. Lahar-zone communities (Pierce County runs the nation’s best program) have marked evacuation routes to high ground and practice them — lahars from Rainier could reach populated valleys in under an hour, and detection systems buy only minutes. Drill it like coastal towns drill tsunamis.
  • Take USGS alert levels seriously. Volcanoes, unlike earthquakes, usually give weeks of instrumental warning (swarms, deformation, gas). When an observatory raises an alert level or officials order evacuation, the science behind it is strong — St. Helens’ 1980 death toll would have been far higher without the closures.
  • For ashfall: stay indoors, seal gaps, run nothing that ingests air (vehicle engines, HVAC without filtration), wear an N95 outside, and clear roofs promptly — wet ash is heavy enough to collapse them. Keep vehicles garaged; ash destroys engines and paint.
  • In Hawaii: respect lava-zone disclosure when buying, carry the state’s volcano-specific insurance where available, and treat vog (volcanic smog) as a real respiratory hazard during active phases.
  • Aviation and ash don’t mix — eruption-related flight cancellations are the one way this hazard touches most Americans; build slack into travel through Anchorage or Seattle during unrest.

Sources

See the US counties with the highest volcanic activity risk →

← All guides