strata collective term for layers of sedimentary rock.
stratification the layering of sedimentary rock, with changes of color or texture from one bed to the next.
stratigraphy the study of rock layers, their ages, and how they were laid down or deposited.
stratum a single layer of sedimentary rock.
subduction the descending of one lithospheric plate under another.
subduction zone the area where one lithospheric plate descends beneath another, known by a high frequency of earthquakes.
syncline strata bent downward in an upside-down arch; the reverse of an anticline.
taphonomy the study of the history of a fossil, from the time the organism is first preserved through when it is uncovered by a paleontologist. Skeletons, for example, may become disarticulated because of water flow, or some fossils may become flattened due to compression by a glacier or the accumulation of many layers of sediment.
tectonic referring to the actions of the Earth's crust.
terrane a piece of the Earth's crust that tears off from one tectonic plate and becomes attached to another.
thermal plume in the upper mantle, a huge column of upwelling magma located in a fixed position and therefore known as a "hot spot." Thought to be responsible for volcanic activity.
topography collective term for the layout and all of the geological features in a given area of the Earth's surface, including hills, mountains, valleys, lowlands, etc.
tor a large rock or pile of rocks rising 6 to 9 meters (19.5-29.5 ft)—actually a mass of granite eroded to give the appearance of individual stones. Seen frequently in England.
trace fossil an incomplete or partially destroyed fossil, or any slight evidence of an organism, such as a tiny burrow or a footprint.
upland any high ground or highland, but not reaching the height of a mountainous area.
uplift the raising up of Earth's crust from tectonic forces. Also the lifted Earth itself.
weathering the gradual erosion of large rocks into smaller ones.
GEOLOGICAL TIME
(The Phanerozoic eon is measured from 544 million years ago to the present. Precambrian time is measured from 4,500 to 544 million years ago.)
m = million years ago
Era Period Epoch
Cenozoic Quaternary Holocene 11,000-present
Pleistocene 1.8m-11,000
Tertiary Pliocene 5m-1.8m
Miocene 23m-5m Oligocene 38m-23m Eocene 54m-38m Paleocene 65m-54m
Mesozoic Cretaceous 146m-65m
Jurassic 208m-146m Triassic 245m-208m
Paleozoic Permian 286m-245m
Carboniferous 360m-286m Pennsylvanian 325m-286m Mississippian 360m-325m Devonian 410m-360m Silurian 440m-410m Ordovician 505m-440m Cambrian 544m-505m
Proterozoic Neoproterozoic 900m-544m
Mesoproterozoic 1,600m-900m Paleoproterozoic 2,500m-1,600m
Archean
(3,800m-2,500m)
Hadean
(4,500m-3,800m)
glaciers and ice
ablation the melting and evaporation of ice from a glacier.
arete a steep-sided, serrated mountain ridge formed by glacial erosion.
bergschrund the crevasse or group of crevasses where the head of a glacier is pulling away from a mountain wall.
bergy bit National Weather Service's term for a broken-off chunk of iceberg, bobbing 3-16 feet (1-5 m) above the surface of the water and extending 1,076-3,229 square feet (100-300 sq m) across.
black ice any thin patch of roadway ice that tends to be so clear it is nearly invisible and consequently causes numerous car accidents.
brash ice fragments of floating, broken ice, measuring less than 6.5 feet (2 m) across.
calving the breaking away of large chunks of ice from the end of a glacier; in tidewater glaciers the fallen chunks become icebergs.
cirque a bowl-like or amphitheater-like depression in the side of a mountain, formed by glacial movement.
cold glacier a glacier with no surface melting during summer months; its temperature is always below freezing. See warm glacier.
crevasse a crack or fracture in a glacier.
dendrochronology the study of a tree's growth rings to determine past climatic changes and fluctuations in glacial movement and growth.
drift rocks and gravel carried by glaciers and eventually deposited. Also known as till.
drift ice any ice floating on the surface of a body of water.
drumlin an elongated hill consisting of compacted drift or till left by a glacier.
dust well a hole in the surface of a glacier, formed by a clump of dirt or dust that absorbs more sunlight and melts surrounding ice.
erratic a glacially deposited rock that differs from native rocks.
esker a long, winding ridge of till deposited by water flowing through a glacial tunnel.
fjord a glacier-carved valley inundated by the sea to form a long, narrow inlet. Also spelled fiord.
firn granular snow a year old or more at the accumulation zone or head of a glacier.
floe a large slab of sea ice sometimes measuring several miles across and usually consisting of many small ice chunks frozen together.
glacial lakes lake basins carved out by glacial activity. These include (1) rock basin lake, a depression ground out of bedrock; (2) cirque lake, a lake in the side of a mountain, also known as a tarn; (3) moraine lake, formed when glacially dumped drift dams a river or stream; (4) kettle lake, formed within a depression in the moraine itself; (5) ice-dammed lake, formed when the glacier itself dams a stream.
glacial pavement bedrock paved over by glaciers, leaving telltale scrapes, scars, gouges, or a polished appearance.
glaciation the covering and altering of the land by glacial ice.
glacier a mass of accumulated, compacted snow consolidating into ice. A glacier forms when more snow falls than melts over several successive seasons. Types of glaciers include (1) ice sheet, a large sheetlike glacier spreading out in all directions; (2) continental glacier, an ice sheet that covers a large portion or all of a continent, such as the Antarctic ice sheet; (3) valley glacier, a glacier confined to a valley; (4) cirque glacier, a glacier confined to a cirque; (5) piedmont glacier, the glacial portion that emerges from the mouth of a valley and surrounds the foot of a mountain.
glaciere a cave in a glacier.
glaciologist one who studies ice in all its forms.
glaciology the study of ice in all its forms.
glaciospeleology the study of glacier caves.
growler a small chunk of ice, measuring no more than 215 square feet (20 sq m), broken off from an iceberg.
hanging glacier a glacier that has positioned itself on a high shelf and hangs over a valley, posing a major avalanche danger.
hanging valley a secondary valley whose floor is much higher than the larger valley into which it leads; originally formed by a small, tributary glacier leading to a larger one.
horn a sharp, steeply descending peak formed by the headwalls of three or more cirques.
hummock a mound of broken ice, pushed up by pressure.
hummocked ice pieces of broken ice forced atop one another by pressure and forming a mound.