Thursday, November 23rd, 2017

* Talus- A slope formed a the base of a steeper slope, made of fallen and disintegrated materials.
* Talus-An accumulation of loose angular rocks at the base of a cliff from which they have been cleared by mass wasting.
* Tarn-A small lake at the base of a cirque.
* Tectonic plate-A large segment of the Earth's outermost, cool, rigid shell, consisting of the lithosphere and overlying crust. Tectonic plates float on the weak, plastic asthenosphere.
* Tectonic -The deformation forces acting on a planet's crust.
* Tectonics-A branch of geology dealing with the broad architecture of the outer part of the Earth; specifically the relationships, origins, and histories of major structural and deformational features.
* Temperature Inversion- A layer of air in which the temperature increases with height. Meteorological convention considers temperature decreasing with height as the norm, thus when temperature decreases with height, it is inverted. There are four common causes of a temperature inversion- radiational cooling, advection of warm air over cold air as in frontal situations, advection of warm air over a cold surface such as snow or ice, and subsidence, the sinking of air which is then warmed by compression.
* Temperature Profiles- The change of air temperature with height above the ground. When the temperature increases with height, the profile is called an inversion profile, or simply an inversion. When the temperature decreases strongly with height, a convective profile may be established
* Tensional stress-Stress that pulls rock apart and is the opposite of tectonic compression.
* Terminal moraine-An end moraine that forms when a glacier is at its greatest advance.
* Terminator -The dividing line between the illuminated (day) and the unilluminated (night) part of the moon's or a planet's disk.
* Terminus-The end, or foot of a glacier.
* Terrestrial planets- another name for inner planets; they have a rocky crust, a dense mantle layer, and a very dense core.
* Terrestrial planets-The four Earthlike planets closest to the Sun (Mercury, Venus, Earth, and Mars) which are composed primarily of rocky and metallic substances.
* Terrigenous sediment-Sea-floor sediment derived directly from land.
* Texture- characteristic structure of a rock given by its size, shape, and arrangement of its mineral crystals.
* Texture-The size, shape, and arrangement of mineral grains, or crystals in a rock
* The fundamental unit of elements consisting of a small, dense, positively charged center called a nucleus surrounded by a diffuse cloud of negatively charged electrons.
* Thermal- A rising parcel of warm, and less dense, air generally produced when the Earth's surface is heated or when cold air moves over a warmer surface such as warm water.
* Thermocline-A layer of ocean water between 0.5 and 2 kilometers deep where the temperature drops rapidly with depth.
* Thermosphere- the layer of Earth's atmosphere above the mesosphere.
* Thermosphere-An extremely high and diffuse region of the atmosphere lying above the mesosphere. Temperature remains constant and then rises rapidly with elevation in the thermosphere.
* Threshold effect-A threshold effect occurs when the environment initially changes slowly (or not at all) in response to a small perturbation, but after the threshold is crossed, an additional small perturbation causes rapid change.
* Thrust fault-A type of reverse fault with a dip of 45 degrees or less over most of its extent.
* Thunder- The sound emitted from a lightning channel during a lightning discharge caused by rapidly expanding gases. The sound can have a number of different characters- roll, rumble, crack, crash, series of short bursts.
* Thunderheads- A popular term referring to the anvil top of cumulonimbus clouds.
* Thunderstorm/Thundershower- A local storm produced by a cumulonimbus cloud that contains thunder and lightning and often strong wind gusts, heavy rain showers and, at times, hail. A thundershower is a popular term usually applied to a mild thunderstorm. There are three main types of thunderstorms, classed by the mechanism that triggers them- advection thunderstorm, air-mass thunderstorm, frontal thunderstorm.
* Tidal current-A current caused by the tides.
* Tidal forces -The gravitational pull on planetary objects from nearby planets and moons. When the tidal forces of a planet and several moons are focused on certain moons, particularly if the orbits of the various objects bring them into alignment on a repeated basis, the tidal forces can generate a tremendous amount of energy within the moon. The intense volcanic activity of Io is the result of the interaction of such tidal forces.
* Tidal heating -The frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and possibly neighboring satellites.
* Tidal range- the difference in level between the low and high tide in a given area.
* Tides- the daily rise and fall of ocean waters due to the gravitational pull of the moon (and to a lesser degree, the sun).
* Tide-The cyclic rise and fall of ocean water caused by the gravitational force of the Moon and, to a lesser extent of the Sun.
* Tidewater glacier-A glacier that flows directly into the sea.
* Till (glacial)- General term for material deposited by a glacier. See also moraine.
* Till-Sediment deposited directly by glacial ice and that has not been resorted by a stream.
* Time correlation-Correlation based on age equivalence of rock units.
* Time-travel curve-A curve that records arrival times of P and S earthquake waves, used to measure the distance from a recording station to an earthquake epicenter.
* Time-Travel Graph - a graph that shows the relationship between P and S wave travel times and epicenter distance.
* Topsoil - The A-horizon of soil; contains organic material (humus) that forms from decayed plant and animal materials.
* Topsoil-The fertile, dark-colored surface soil, or A horizon.
* Tornado- A violently rotating column of air, a vortex, formed in a thunderstorm which is in contact with both the parent cloud and the ground with a diameter between tens and hundreds of meters The lifetime of a tornado is usually less than an hour, but some have been observed to last several hours. Wind speeds are usually above 64 km/h (40 mph) and can reach over 500 km/h (300 mph). The intensity of tornado damage is reported using the Fujita Scale.
* Tornado Alley- An area of the United States where tornadoes are the most frequent encompassing the lowlands of the Mississippi, Ohio and lower Missouri River valleys. Tornado Alley is generally considered to be the states of Texas (northern part), Oklahoma and Kansas.
* Tornado Outbreak- A tornado outbreak occurs when a large number (six or more) of tornadoes are formed in groups or individual storms within a 24-48-hour period over a specific geographical area and spawned from the same general weather system. Tornado outbreaks are classified into three categories- local outbreaks , line outbreaks and progressive outbreaks .
* Tornado-A small, intense, short-lived, funnel-shaped storm that protrudes from the base of a cumulonimbus cloud.
* Trade winds - Winds that originate in the horse latitudes and blow toward the doldrums.
* Trade winds-The winds that blow steadily from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere between 5 degrees and 30 degrees north and south latitudes.
* Transform boundary-A boundary between two lithospheric plates where the plates are sliding horizontally past one another.
* Transform fault-A strike-slip fault between two offset segments of a mid-oceanic ridge.
* Transpiration-Direct evaporation from the leaf surfaces of plants.
* Transported soil - soil that formed from parent material left by winds, rivers, or glaciers; or soil that itself was moved from its original location.
* Transport-The movement of sediment by flowing water, ice, wind, or gravity.
* Transverse dune-A relatively long, straight dune with a gently sloping windward side and a steep lee face that is orientated perpendicular to the prevailing wind.
* Tremor- Low amplitude, continuous earthquake activity often associated with magma movement.
* Trench-A long, narrow depression of the sea floor formed where a subducting plate sinks into the mantle.
* Tributary-Any stream that contributes water to another stream.
* Tropic of Cancer-The latitude 23.5 degrees north of the equator. On June 21, the summer solstice in the Northern Hemisphere, sunlight strikes the Earth from directly overhead at noon at this latitude.
* Tropic of Capricorn-The latitude 23.5 degrees south of the equator. On December 22, the summer solstice in the Southern Hemisphere, sunlight strikes the Earth from directly overhead at noon at this latitude.
* Tropical cyclone-A broad, circular storm with intense low pressure that forms over warm oceans, (also called a hurricane, typhoon, or cyclone).
* Tropical Depression- A tropical cyclone in which the maximum 1-minute sustained surface wind is 61 kilometers per hour (38 mph) or less. They form from a tropical wave or tropical disturbance.
* Tropical Disturbance- A discrete system of apparently organized convection originating in the tropics or subtropics, having a non-frontal migratory character and maintaining its identity for 24 hours or more.
* Tropical Storm- A tropical cyclone in which the 1-minute sustained surface wind ranges 62 to 117 kilometers per hour (39 to 73 mph) .
* Tropopause- The boundary between the troposphere and stratosphere found between 8 to 20 km in altitude. The tropopause is higher over the tropics and lowest in the polar regions. It is characterized by an abrupt increase in temperature (the stratospheric temperature inversion). The tropopause generally marks the vertical limit of most clouds and storms.
* Tropopause-The boundary between the troposphere and the stratosphere.
* Troposphere- The layer of the atmosphere from the Earth's surface up to the tropopause, characterized by decreasing temperature with height, appreciable vertical wind motion and considerable water vapor content. Most of what we sense as weather (most clouds, rain, etc.) occurs in the troposphere.
* Troposphere-The layer of air that lies closest to the Earth's surface and extends upward to about 17 km. Temperature generally decreases with elevation in the troposphere.
* Trough- An elongated area of relatively low atmospheric pressure. Also the lowest portion of a wave found between the wave crests.
* Trough-The lowest part of a wave.
* Truncated spur-A triangular-shaped rock face that forms when a valley glacier cuts off the lower portion of an arete.
* Tsunami- A great sea wave produced by a submarine earthquake, volcanic eruption, or large landslide. Commonly (but erroneously) called a "tidal wave," tsunamis can cause great damage due to flooding of low coastal areas.
* Tsunami-A large sea wave, produced by a submarine earthquake or a volcano, characterized by long wavelength and great speed.
* Turbidity current-A rapidly flowing submarine current laden with suspended sediment, that results from mass wasting on the continental shelf or slope.
* Turnover-A process, usually occurring in fall and spring in temperate-climate lakes, in which convection mixes lake water so that it becomes of uniform temperature from top to bottom of the lake.

* Ultimate base level-The lowest possible level of downcutting of a stream, usually sea level.
* Ultramafic rock-Rock composed mostly of minerals containing iron and magnesium for example, peridotite.
* Ultraviolet Radiation- Ultraviolet radiation (UV) is one form of radiant energy coming from the sun. The sun emits a range of energy known as the electromagnetic spectrum. The various forms of energy, or radiation, are classified according to wavelength (measured in nanometers (nm) where one nm is a millionth of a millimeter). The shorter the wavelength. The more energetic the radiation. In order of decreasing energy, the principal forms of radiation are gamma rays, X-rays, UV (ultraviolet radiation). Visible light, infrared radiation, microwaves, and radio waves. Ultraviolet, which is invisible, is so named because it occurs next to violet in the visible light spectrum. Ultraviolet radiation contains the wavelengths between 30 and 400 nm. The sun radiates short-wave energy which includes the UV bands. Most is absorbed in the ozone layer. UV radiation is generally hazardous to life on Earth, causing damage to DNA. Human beings get a sunburn from the ultraviolet rays emitted by the Sun.
* Umbra -A) The dark central region of a sunspot. B) The darkest part of a shadow
* Umbra-The part of an eclipse shadow where the Sun is completely eclipsed.
* Unconformity- A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic succession, such as an interruption in continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata. It results from a change that caused deposition to cease for a considerable time, and it normally implies uplift and erosion with loss of the previous formed record.
* Unconformity-A gap in the geological record, such as an interruption of deposition of sediments, or a break between eroded igneous and overlying sedimentary strata, usually of long duration.
* Underground mine-A mine consisting of subterranean passages that commonly follow ore veins or coal seams.
* Underthrusting-The process by which one continent may be forced beneath the other during a continent-continent collision.
* Uniformitarianism - A fundamental principle of geology, which states that we can understand geologic events of the past by looking at geologic events of the present. According to uniformitarianism, a volcano eruption that happens today is pretty much like a volcano eruption that happened million years ago.
* Uniformitarianism-The principle that states that geological processes and scientific laws operating today also operated in the past and that past geologic events can be explained by forces observable today. "The present is the key to the past." The principle does not imply that geologic change goes on at a constant rate, nor does it exclude catastrophes such as impacts of large meteorites.
* Unit cell-The smallest group of atoms that perfectly describes the arrangement of all atoms in a crystal, and repeats itself to form the crystal structure.
* Unsaturated zone-A subsurface zone above the water table that may be moist but is not saturated; it lies above the zone of saturation. (syn: zone of aeration)
* Unstable Air- An atmospheric state where strong vertical motions are produced by displacement of a parcel of air that accelerates upward when the parcel is moved upward, or downward when the parcel is moved downward. Usually found in regions of the atmosphere where a convective temperature profile is found.
* Upper mantle-The part of the mantle that extends from the base of the crust downward to about 670 kilometers beneath the surface.
* Upslope fog-Fog that forms when air cools as it rises along a land surface.
* Upwelling - The process by which water rises from a lower to a higher depth, usually as a result of divergence and offshore currents. It influences climate by bringing colder, more nutrient-rich water to the surface. A vital factor of the El NiƱo event.
* Upwelling-A rising ocean current that transports water from the depths to the surface.
* Urban heat island effect-A local change in climate caused by a city.
* U-shaped valley-A glacially eroded valley with a characteristic U-shaped cross section.

* Valley train-A long and relatively narrow strip of outwash deposited in a mountain valley by the streams flowing from an alpine glacier.
* Vapor (water)- Water in the gaseous state.
* Vaporization- The movement of liquid water (or any other liquid) into the gaseous or vapor state. Also called evaporation.
* Vent -The opening in the crust through which volcanic material erupts.
* Vent-A volcanic opening through which lava and rock fragments erupt.
* Vernal- Pertaining to the Spring season. The Vernal Equinox occurs on or about March 21 in the Northern Hemisphere and on or about September 21 in the Southern Hemisphere. See Equinox.
* Vesicle- A small air pocket or cavity formed in volcanic rock during solidification.
* Vesicle-A bubble formed by expanding gases in volcanic rocks.
* Vesicular basalt- Holes 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.
* Viscosity- A measure of resistance to flow in a liquid (molasses in January has high viscosity while molasses in August has lower viscosity).
* Volatile-A compound that evaporates rapidly and therefore easily escapes into the atmosphere.
* Volcanic Arc- A generally curved linear belt of volcanoes above a subduction zone, and the volcanic and plutonic rocks formed there.
* Volcanic neck-A vertical pipe-like intrusion formed by the solidification of magma in the vent of a volcano.
* Volcanic rock-A rock that formed when magma erupted, cooled, and solidified within a kilometer or less of the Earth's surface.
* Volcano- A vent in the surface of the Earth through which magma and associated gases and ash erupt; also, the form or structure (usually conical) that is produced by the ejected material.
* Volcano-A hill or mountain formed from lava and rock fragments ejected through a volcanic vent.
* Vulcan- Roman god of fire and the forge after whom volcanoes are named.