A Nature study mapped the top of Yellowstone’s magma reservoir at 3.8 kilometers, or 2.4 miles, beneath the northeastern caldera, identifying a sharp gas-rich cap that acts as a natural lid.
More than 600 seismic sensors and a 53,000-pound vibroseis truck let researchers image the cap, which is made of partly molten rock and supercritical-water bubbles and is only slightly porous.
That limited porosity matters because it vents gas gradually through geysers, hot springs and fumaroles, stabilizing underground pressure instead of letting it build toward an eruption.
Researchers said Yellowstone is still an active, dynamic system with explosive rhyolitic magma below the cap, but the new map improves monitoring and provides a stronger baseline for early warning.