Glossary

andesite - a fine-grained, extrusive volcanic rock named after the Andes mountain chain

arête - a sharp ridge formed from the carving action of head- or sidewalls of two glaciers on opposite sides of a ridge

bergschrund - a crevasse near the head of a glacier

cirque - the French term for a basin carved out by a glacier due to plucking; other terms for cirque include corrie (Scottish), cwm (Welsh), and nitsch (German)

col - a saddle in an arête formed where a glacier overrode the ridge

composite volcano - a type of volcano composed of alternating layers of ash and lava

dacite - a thick, igneous rock ejected at the earth's surface

glaciofluvial - meltwater from glaciers and their deposition

Holocene - the current epoch of the Quaternary Period of the Cenozoic Era which began about 10,000 years ago; another name for Holocene is Recent

horn - a peak formed by three or more cirques eroding back until their headwalls become the sides of the peak

jökulhlaup - the Icelandic term (pronounced yo-kool-loop) for glacial outburst floods. Although this term has been used by California geologists for mudflows in our area, the original Icelandic term only referred to outburst floods due to volcanic activity causing glacial ice to melt.

lahar - pyroclastic material deposited at the base of a volcano

Little Ice Age - a cold period during the 1500s to mid-1800s peaking about 1750

moraines - glacial deposits usually found at the side or end of a glacier

mudflow - a type of debris flow which contains a high amount of water, clays, and silts, usually along with larger material

neoglacial - glaciation which occurred after the Ice Age during the Holocene

Pleistocene - An epoch of the Quaternary Period of the Cenozoic Era which occurred between 10,000 and 2 million years ago, often associated with the Ice Age

plug dome - a volcano with steep sides formed from pasty lava "squeezed" out of a central vent; plug domes are relatively small volcanoes; Black Butte provides a local example of a plug dome

Quaternary - The most recent period of the Cenozoic Era which began about 2 million years ago; the two epochs of the Quaternary include the Holocene (the present epoch) and the Pleistocene, which lasted from about 2 million years ago to about 10,000 years ago

Recent - another term equivalent to Holocene, the present geologic epoch beginning about 10,000 years ago

strato-volcano - another term for composite volcano, one made up of alternating layers of ash and lava