Marker Name: The Pinnacles
Marker Text: The history of the “pinnacles” below began about 7,700 years ago when the eruptions of Mt. Mazama were reaching their climax. Torrents of red-hot, gas-charged pumice poured down Mazama’s slopes at speeds of up to 100 mph (160 kph). On top of this came a flow of heavier rocks called scoria. These glowing avalanches flooded downslope for many miles, leaving deep deposits in their wake.
Temperatures in the deposits may have exceeded 750° F (400° C). Plumes of vapors appeared, as gasses escaped from the settling rocks through vents called fumaroles. Minerals in the gasses, combined with extreme heat, welded the sides of the fumaroles in the shape of slender cones. Since then, streams have eroded a canyon through the deposits, exposing the cones. Many of these fossil fumaroles are hollow.
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