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.