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Earth Science

snirtballa combination of snow and dirt. snirtballs are produced by accident when the total snowfall on bare ground is less than 0.537 inches.
snockballa combination of snow and rock
glacial quarrying (plucking)a common mechanical weathering process in alpine glaciated terrain where glacial ice frozen into cracks in the bedrock literally "pluck" rock material from the valley floor.
harmonic tremora continuous release of seismic energy typically associated with the underground movement of magma. it contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage along a fault.
glacial abrasiona copmmon mechanical weathering process where rock and debris frozen into the sides and bottom of a glacier act like sandpaper and wear down the bedrock the glacier is mocing across.
marker horizon (or bed)a distinctive horizon which is used for regional correlation of lithology. a good marker horizon is distinctive, widespread, and represents a relatively short period of geologic time. for example, ash from a volcanic eruption, debris from a meteorite impact, etc. it is geoman`s opinion that humans will represent one of the earth`s finest marker horizons in the geologic record of the future. our effect on the surface is certainly distinctive and widespread, and, at the rate we are going, it is likely that our species will have a relatively short lifespan (speaking in terms of geologic time, of course).
debris avalanchea flow of unsorted masses of rock and other material downslope under the influence of gravity. water is commonly involved as a catalyst and/or lubricant. for example
mudflowa flowage of water-saturated earth material possessing a high degree of fluidity during movement. a less-saturated flowing mass is often called a debris flow. a mudflow originating on the flank of a volcano is properly called a lahar.
alluviuma general term for clay, silt, sand, gravel or similar unconsolidated material deposited by a stream or other body of running water.
shield volcanoa gently sloping volcano in the shape of a flattened dome, built almost exclusively of mafic lava flows. the hawaiian islands are a good example.
aquitarda geologic formation or stratum that significantly retards fluid movement.
plutona large igneous intrusion formed at great depth in the crust.
strike-slip faulta nearly vertical fault with side-slipping displacement.
sniceballa snowball which has been stored in the freezer for several months (or more). useful for surprising unwelcome visitors during the spring and summer months.
composite volcanoa steep volcanic cone built by both lava flows and pyroclastic eruptions.
lahara torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. a type of mudflow.
lava tubea tunnel formed when the surface of a mafic lava flow cools and solidifies, while the still-molten interior flows through and drains away. these can insulate the flow and allow it to travel great distances.
ash flowa turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure. the mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes, or even along a level surface.
fumarolea vent or opening through which issue steam, hydrogen sulfide, or other gases. the craters of many dormant volcanoes contain active fumaroles.
cinder conea volcanic cone built entirely of loose fragmented material (pyroclastics.)
active volcanoa volcano that is erupting; or one that, while not erupting at the present, has erupted within (geologically) recent time and is considered likely to do so in the (geologically) near future.
extinct volcanoa volcano that is not presently erupting and is not likely to do so for a very long time in the future.
grabenan elongate crustal block that is relatively depressed (downdropped) between two fault systems.
flank eruptionan eruption from the side of a volcano (in contrast to a summit eruption.)
absolute datean estimate of the true age of a mineral or rock based on the rate of decay of radioactive minerals.
horizontal blastan explosive eruption in which the resultant cloud of hot ash and other material moves laterally rather than upward.
phreatic eruption (explosion)an explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks. magma is not involved.
noritean igneous rock with mafic composition.
aquicludean impermeable geologic formation or stratum which will not hold or transmit fluid.
seismographan instrument that records seismic waves; that is, vibrations of the earth. used to record and measure earthquakes.
lava flowan outpouring of lava onto the surface from a vent or fissure. also, a solidified tongue-like or sheet-like body formed by outpouring lava.
hydrothermal reservoiran underground zone of porous rock containing hot water.
brecciaangular fragments of material, commonly formed by physical weathering processes or explosive volcanic activity.
geothermal energyenergy derived from the internal heat of the earth.
chattermarkserosional features associated with alpine glaciers.
fossilevidence of past life on earth. can include the preserved hard and soft parts of plants and animals, tracks and burrows, whole organisms preserved intact in amber or tar, and fossilized dung. any evidence of life constitutes a fossil.
rock flourfinely ground rock material, usually associated with glaciers (or faults). can be mixed with water and formed into loaves which, when baked for 45 minutes at 350°, are totally unedible.
metamorphicfrom the greek "meta" (change) and "morph" (form). commonly occurs to rocks which are subjected to increased heat and/or pressure. also applies to the conversion of snow into glacial ice.
morainegeneral term for material deposited beneath, along the sides, and/or at the terminus of a glacier. also, what we get here in oregon during the fall, winter, and spring. see also till.
drift (glacial)general term for material deposited by a glacier.
till (glacial)general term for material deposited by a glacier. see also moraine.
striations (glacial)grooves eroded into bedrock by rock debris frozen into the base of a glacier.
pahoehoehawaiian term for a fluid volcanic eruption resulting in broad basaltic shield volcanoes. the highly fluid magma flows readily, and hardens into ropey forms as it cools. it can be very impressive to view an active flow!
vesicular basaltholes and other openings in basaltic flow which are the result of trapped gas bubbles. vesicles are often filled at a later date with a wide variety of materials, including, quartz, agate, zeolites, and many other minerals.
pillow lavainterconnected, sack-like bodies of lava that form underwater.
andesiteintermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium. andesite minerals commonly include plagioclase and hornblende, with lesser amounts of mica, pyroxene, and various accessory minerals. andesites are aphanitic in texture and are usually medium dark in color. they occur with composite volcanic cones associated with convergent plate margins.
erratic (glacial)large rocks or other debris deposited by a glacier, usually in an area far removed from its source. commonly used to indicate a big chunk of debris which is clearly out of place and shouldn`t even be where it is.
pyroclastic flowlateral flowage of a turbulent mixture of hot gases (≈400°c) and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at high speed (100 miles an hour or more). also known as a "glowing avalanche" or "nueé ardente."
pumicelight-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles.
lapilliliterally, "little stones;" round to angular rock fragments measuring 1/10 inch to 2-1/2 inches in diameter, which may be ejected in either a solid or molten state.
weathering (surface)making little ones out of big ones. waethering includes the processes which mechanically and chemically break down the mountains into little pieces, so they can be eroded and transported to the beach (see strickler`s 3rd law of geofantasy).
ejectamaterial that is thrown out by a volcano, including pyroclastic material (tephra) and, from some volcanoes, lava bombs.
tephramaterials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air.
magmamolten rock beneath the surface of the earth.
glacial icenaturally occurring ice which exhibits internal plastic flow and deformation.
pyroclasticpertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.
glacial polishpolished bedrock surfaces left behind after melting of glacial ice. the polishing is probably due to very fine grained rock flour carried at the base of the ice.
geothermal powerpower generated by using the heat energy of the earth.
tuffrock formed of pyroclastic material.
vulcanroman god of fire and the forge, after whom volcanoes are named.
continental crustsolid, outer layers of the earth, including the rocks of the continents.
volcanic necksolidified lava that fills the conduit of a volcano. volcanic necks (also called plugs) are usually more resistant to erosion than the material making up the surrounding cone, and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.
di-polarthe arrangement of the hydrogen atoms of a water molecule at 105 deg. across the oxygen results in a slight electrical charge to the molecule. it also results in water molecules looking like mickey mouse instead of alfred e. newman.
eruption cloudthe column of gases, ash, and larger rock fragments rising from a crater or other vent. if it is of sufficient volume and velocity, this gaseous column may reach many miles into the stratosphere, where high winds will carry it long distances.
oceanic crustthe earth`s crust where it underlies oceans.
kinetic energythe energy of motion.
brittle-ductile transition zonethe location at depth within the earth`s crust where the temperature and pressure have risen to such a high level that directed stress results in plastic deformation as opposed to fracturing and faulting.
floodplainthe low relief lands bordering a stream or river, common to the mature and old age stages of stream development. floodplains store excess water in times of high water, and excess sediments in times of low water. beware of building your dream house on a floodplain - they tend to get rather wet at irregular intervals.
snowlinethe lower limit of any year`s permanent snowfall. separates the zone of accumulation from the zone of ablation.
seafloor spreadingthe mechanism by which new seafloor crust is created at oceanic ridges and slowly spreads away as tectonic plates separate.
eruptive ventthe opening through which volcanic material is emitted.
adiabatic ratethe rate of temperature change in the atmosphere due to the raising or lowering of an air mass. the "dry adiabatic rate" is 5.5 deg. f. per 1000 feet, while the "wet" rate is 3.5 deg. f. per 1000 feet.
calderathe spanish word for cauldron, a basin-shaped volcanic depression; by definition, at least a mile in diameter. such large depressions are typically formed by the subsidence of volcanoes. crater lake occupies the best-known caldera in the cascades.
plug domethe steep-sided, rounded mound formed when viscous lava wells up into a crater and is too stiff to flow away. it piles up as a dome-shaped mass, often completely filling the vent from which it emerged.
potential energy (gravitational)the stored energy of a substance. water has a lot of this if there is an elevation difference. potential energy can be converted to kinetic energy if the water (or other substance) is allowed to move.
biostratigraphythe study and classification of rocks and their history based on their fossil content.
magma chamberthe subterranean cavity containing magma. when a conduit is opened to the surface, a volcanic eruption is possible.
detachment planethe surface along which a landslide disconnects from its original position.
continental driftthe theory that horizontal movement of the earth`s surface causes slow, relative movements of the continents toward or away from one another.
hydrologic cyclethe transfer of water between numerous temporary storage reservoirs. these include the ocean, rivers and streams, glacial ice, beer cans, dogs and cats, groundwater, and the atmosphere.
water cyclethe transfer of water between numerous temporary storage reservoirs. these include the ocean, rivers and streams, glacial ice, beer cans, dogs and cats, groundwater, and the atmosphere.
artificial rechargethe unnatural addition of surface waters to groundwater. recharge could result from reservoirs, storage basins, leaky canals, direct injection of water into an aquifer, or by spreading water over a large land surface.
isostasythe vertical readjustment of the surface of the earth due to the addition or removal of weight. commonly associated with the advance and retreat of glacial ice.
subduction zonethe zone of convergence of two tectonic plates, one of which usually overrides the other.
dormant volcanothis term is used to describe a volcano which is presently inactive but which may erupt again. the major volcanic cones of the cascade mountains (in washington, oregon, and california) are believed to be dormant rather than extinct.
loessvery fine-grained sediments deposited by wind action. commonly associated with the margins of continental ice sheets. large expanses of loess from the recent ice age are in large part responsible for the bountiful corn and wheat fields of the american midwest.
ashfall (subaerial)volcanic ash that has fallen through the air. the resulting deposit is usually well sorted and exhibits a finely layered structure.
dacitevolcanic rock (or lava) that characteristically is light in color and contains 62 to 69 percent silica and moderate amounts of sodium and potassium.
rhyolitevolcanic rock (or lava) that characteristically is light in color, contains 69 percent silica or more, and is rich in potassium and sodium. it is fine grained, which although different in texture, has the same composition as granite
basaltvolcanic rock (or magma) that is generally dark in color, contains 45 to 54 percent silica, and is rich in iron and magnesium. an eruption of basaltic magma is generally quiet, and results in flows (both vesicular and non-vesicular) and breccias. undersea eruptions commonly result in the formation of "pillow lavas." basalt represents the initial differentiated material erupted by the earth at spreading centers, and is considered by geoman to be the "blood of the earth."
hot-spot volcanoesvolcanoes related to a persistent heat source in the mantle.
vapor (water)water in the gaseous state.
connate waterwater included in the groundwater which is derrived from the rock itself, as opposed to water which has percolated down from the surface.
evapotranspirationwater used by plants and animals and subsequently returned directly to the atmosphere.