alluvial - stream deposited material

alluvial cone - fan-shaped alluvial deposits at the base of a slope; also called alluvial fan

alpine glacier - a mountain glacier, as opposed to an ice cap or ice sheet

andesite - a volcanic rock named after the Andes mountain chain

arête - a sharp mountain ridge formed from the plucking action of two glaciers on opposite sides of the ridge

bergschrund - a crevasse near the head of a glacier

Cenozoic - The current geological era which began about 65 million years ago

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 from a glacier on one side flowing to the other side of the ridge.

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

crevasse - a typically vertical crack in a glacier which comes in many forms

dacite - an igneous rock ejected at the earth's surface, kind of like liquid quartz

debris avalanche - a sudden downslope movement of material down steep slopes, usually because the soil is saturated with water

debris fan - non-sorted stream deposits shaped like a fan at the base of a mountain

debris flow - a general term for fast-moving debris of various sorts

gendarmes - ice towers

geologic time scale - geologic units of time including eras, periods, and epochs

glacial portals - cavernous openings in the debris below the glacier

glacier - ice derived from compacted snow which moves under its own weight, or has in the past

headwall - the steep back side of a cirque basin which formed from glacier ice plucking off the rocks on the upslope side of the drainage basin

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 3 or more cirques eroding back until their headwalls are the sides of the peak

Ice Age - the Late Cenozoic Ice Age which began about 25 million years ago, commonly referred to as the Pleistocene Ice Age

icefall - a steep, jagged area of a glacier

ice stream - an old term for glacier; more precisely, a faster-moving zone of ice flowing within a larger body of ice; fleuve de glace is the French term for ice stream

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

lahars - pyroclastic material deposited at the base of a volcano

Late Cenozoic Ice Age - one of Earth's major ice ages which began 25 million years ago; also called the Ice Age and the Pleistocene Ice Age

lithosphere - the outermost layer of the Earth composed of continental crust, oceanic crust, and the asthenosphere; commonly called the Earth's crust

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

Mathes - the youngest of the three major stages of the Little Ice Age

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

moulin - vertical shaft at the downslope end of a transverse fissure

mud flow - 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

plate - large pieces of the lithosphere which move under the influence of convective currents driven by radioactivity in the interior of the Earth

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

Pleistocene Ice Ages - a major ice age which began about 25 million years ago; also referred to as the Ice Age or, more properly, the Late Cenozoic 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

plucking - the removal of rock material by flowing ice, which adheres to the rock and pulls it off as the ice moves along

pyroclastic - gaseous volcanic material

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

rock flour - rock which has been finely ground by glaciers

serac - a region on a glacier covered with ice towers

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

striations - grooves in rock carved by glacial ice scouring the surface

subduction - the movement of a heavier plate beneath a lighter plate, resulting in the formation of volcanoes (among other things)

Tahoe Glaciation - a glacial period during the late Pleistocene

Tioga Glaciation - a glacial period which occurred after the Tahoe Glaciation during the late Pleistocene

transverse fissure - a vertical crevasse in a glacier which runs in an upslope-downslope direction

valley glacier - an alpine glacier which becomes large enough to flow out of the cirque basin and into the valley below.