Some 20,000 years ago, a volcanic eruption sent gouts of lava into what is now Northern California’s Hat Creek Valley. This molten rock, like any liquid, flowed downhill, gravity pulling it into the lowest channels. These rivers moved slowly, the sides and top cooling as they touched ground and air. A hardened skin slowly formed around the molten flow, creating a rock tube through which the still-liquid lava continued its downward movement. If the gradient was steep enough—and the viscosity low enough— Continue reading “Subway Cave”
