Idaho volcanic activity risk
Ada County has the highest volcanic activity risk in Idaho, scoring 74.3 out of 100 — rated "Very Low" by FEMA's National Risk Index.
| # | County | NRI score | Rating |
|---|---|---|---|
| 1 | Ada County | 74.3 | Very Low |
| 2 | Bonneville County | 72.3 | Very Low |
| 3 | Canyon County | 68.7 | Very Low |
| 4 | Bannock County | 68.1 | Very Low |
| 5 | Bingham County | 67.1 | Very Low |
| 6 | Power County | 66.1 | Very Low |
| 7 | Madison County | 64.5 | Very Low |
| 8 | Jefferson County | 58.3 | Very Low |
| 9 | Butte County | 57.7 | Very Low |
| 10 | Blaine County | 56.7 | Very Low |
| 11 | Lincoln County | 56.4 | Very Low |
| 12 | Twin Falls County | 55.4 | Very Low |
| 13 | Minidoka County | 55 | Very Low |
| 14 | Fremont County | 49.5 | Very Low |
| 15 | Teton County | 47.9 | Very Low |
| 16 | Cassia County | 47.2 | Very Low |
| 17 | Payette County | 46.6 | Very Low |
| 18 | Jerome County | 45.3 | Very Low |
| 19 | Gem County | 45 | Very Low |
| 20 | Owyhee County | 43.6 | Very Low |
| 21 | Washington County | 40.1 | Very Low |
| 22 | Elmore County | 39.7 | Very Low |
| 23 | Gooding County | 34.9 | Very Low |
| 24 | Boise County | 31.9 | Very Low |
| 25 | Custer County | 29.6 | Very Low |
| 26 | Caribou County | 29 | Very Low |
| 27 | Camas County | 28 | Very Low |
| 28 | Bear Lake County | 24.4 | Very Low |
| 29 | Valley County | 23.8 | Very Low |
| 30 | Oneida County | 23.1 | Very Low |
| 31 | Clark County | 22.8 | Very Low |
| 32 | Franklin County | 21.8 | Very Low |
| 33 | Adams County | 16.9 | Very Low |
| 34 | Lemhi County | 13 | Very Low |
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 Idaho:
Frequently asked questions
What is the highest volcanic activity risk county in Idaho?
Ada County, ID has the highest volcanic activity risk in Idaho, with a FEMA National Risk Index score of 74.3 out of 100 (rated "Very Low").
What causes volcanic activity risk in Idaho?
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.