Llao Rock – Prominent Geological Features of Crater Lake National Park
This great mass of dacite (a sluggish lava) was produced from a vent on the upper slopes of Mazama and hardened after moving only a mile or two. The dacite filled in a former explosion crater. This rock rises nearly 2,000 feet above the water- -the highest vertical precipice on the rim- -and was formed by the most massive single flow apparent in the caldera wall, with a maximum thickness of 1,200 feet.
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