Page "Long Valley Caldera" Paragraph 12

All but one of these volcanoes, 1 – 2 million year old Glass Mountain ( made of obsidian ), was destroyed by the major eruption of the area 760, 000 years ago, which released of material from vents just inside the margin of the caldera ( the 1980 Mount St. Helens eruption was.

About half of this material was ejected in a series of pyroclastic flows of a very hot,, mixture of noxious gas, pumice, and ash that covered the surrounding area hundreds of feet ( meters ) deep.

One lobe of this material moved south into Owens Valley, past where Big Pine, California now lies.

Another lobe moved west over the crest of the Sierra Nevada and into the drainage of the San Joaquin River.

The rest of the pyroclastic material along with of other matter, was blown as far as into the air where winds distributed it as far away as eastern Nebraska and Kansas.

However, much of the material ejected straight into the air fell back to earth to fill the deep caldera two-thirds to its rim.