Mount Mazama, the great volcano that preceded
Crater Lake, was built up by successive eruptions
of lava over many thousands of years. Some
lavas oozed or poured from the volcano's top or
sides. Some erupted as red-hot rocks that flooded
down the slopes. Others exploded into the air and
fell as cinders or globs.
You can see the variety of Mt. Mazama's lavas on
the steep caldera wall. Pumice Castle, with its
pinkish-brown "turrets," is the most eye-catching
feature. It's made of layers of pumice and other
rocks coughed up by Mt. Mazama - some so hot
they welded welded together. These air fall deposits
were buried and compacted by other lavas, then
exposed when Mt. Mazama collapsed. A firm
foundation of andesite lava has kept Pumice
Castle intact, while surrounding pumice deposits
have eroded away.
Mt. Mazama is classified as a composite
volcano, a cone built up by lava flows
interspersed with air fall deposits. Pumice Castle
is made of air fall pumice that was laid
down while Mt. Mazama was still growing.