The heat under the volcanoes: Washington's geothermal maps

What the instrument readings actually show

Over the years the Washington Geological Survey has gathered well temperatures, spring chemistry, and heat-flow measurements, and it has taken part in federally funded exploration around the Cascade volcanoes, including temperature-gradient and heat-flow work near Mount St. Helens and Mount Baker. The point of that work is simple. You drill a modest hole, lower a thermometer, and watch how quickly the rock warms with depth, because a fast warm-up hints at a shallow heat source worth a closer look.

Those readings do show elevated temperatures near the volcanoes, which is no surprise. But the data are sparse and local, each number a single point in a very large and rainy landscape, so the maps are best read as a guide to where to look next rather than a promise of power. At last public report the survey still describes Washington's high-temperature geothermal potential as largely unproven at the depths a power plant would need.

Why a volcano is not a power plant

Geothermal electricity needs three things in the same place: heat, water, and rock broken enough to let that water move. A volcano supplies the heat, but the hot rock beneath the Cascades is often either too deep to reach cheaply or too tight to give up steam, and without a natural reservoir of hot water there is nothing to pipe to a turbine. That is the gap between a warm map and a working plant.

Much of the hottest ground also sits where no one will build, inside national parks, wilderness areas, and the Mount St. Helens National Volcanic Monument. Add the cost and risk of deep drilling, and the fact that Washington already has cheap hydropower to compete against, and the math stays hard. Enhanced geothermal, which fractures hot dry rock to make a reservoir, could change that someday, but it is early and unproven here.

Where the heat is already warm enough

Not all useful heat has to spin a turbine. Washington has scattered warm springs, from Sol Duc on the Olympic Peninsula to Carson in the Columbia River Gorge, and in a few places warm water sits shallow enough for direct use, meaning you pipe the hot water itself to heat a building or a pool rather than making electricity from it. These are small, local resources, not a statewide supply.

A ground-source heat pump is a different animal, and it is the one most readers can actually use. It does not tap volcanic heat at all; it moves heat to and from the stable ground a few feet down, which in much of Washington holds steady at roughly 50 degrees year round. That steadiness, not a volcano, is what makes it work, and several utility and state programs offer help with the up-front cost.

Worth watching this month

1. Watch the Washington Geological Survey's publications and online geology portal for any new or revised geothermal maps and well-temperature data, which is routine but the clearest window into what the state actually measures.

2. Watch the U.S. Department of Energy's Geothermal Technologies Office for enhanced-geothermal funding or demonstration news, which matters more for the long run than for this year.

3. Watch the state Department of Commerce and the Clean Energy Transformation Act proceedings for whether geothermal is counted among the non-emitting resources on the path to 2045, a slow process worth tracking.

4. Watch your own utility for ground-source heat pump rebates or direct-use pilots, which is the item most likely to touch your bill in the near term.

5. Watch the USGS for any update to its national geothermal resource assessment, a rare event that would reset how the Northwest's potential is judged.