Montana volcanic activity risk
Carbon County has the highest volcanic activity risk in Montana, scoring 26.1 out of 100 — rated "Very Low" by FEMA's National Risk Index.
| # | County | NRI score | Rating |
|---|---|---|---|
| 1 | Carbon County | 26.1 | Very Low |
| 2 | Gallatin County | 20.5 | Very Low |
| 3 | Park County | 20.2 | Very Low |
| 4 | Madison County | 14 | Very Low |
| 5 | Beaverhead County | 11.7 | Very Low |
| 6 | Big Horn County | 9.4 | Very Low |
| 7 | Stillwater County | 8.1 | Very Low |
| 8 | Sweet Grass County | 0 | No Rating |
Source: FEMA National Risk Index v1.20.0, December 2025. Scores are 0–100 percentile rankings among all US counties. See the methodology page for definitions. Download the full CSV for all counties.
Volcanic Activity risk nationally:
Other hazard risks in Montana:
Frequently asked questions
What is the highest volcanic activity risk county in Montana?
Carbon County, MT has the highest volcanic activity risk in Montana, with a FEMA National Risk Index score of 26.1 out of 100 (rated "Very Low").
What causes volcanic activity risk in Montana?
Volcanic activity risk reflects expected losses from lava flows, tephra fall, lahars (volcanic mudflows), and volcanic gases. The highest-risk counties are in Washington (Mt. Rainier), Oregon (Mt. Hood), and Hawaii (Kilauea, Mauna Loa). Alaska's Aleutian chain contains many active volcanoes affecting nearby communities and trans-Pacific air traffic. Volcanic ashfall events are reported at forecast-zone level in NOAA Storm Events and are not included in county-level counts.