EARTH SCIENCES GLOSSARY

Selected Glossary of Terms: Earth Sciences Danny Vaughn, Ph.D., CMS Absorption band: A range of wavelengths of electromagnetic radiation that are absorbed by the atmosphere or any physical substance. Acceleration: A change in velocity over time. Additive primary colors: Red, green, and blue light (wavelengths of the electromagnetic spectrum) that are reflected and measured with sensory (scanning) instruments. Filters (e.g. blue) of these colors will transmit the primary color (blue) while absorbing the remaining two (red and green). Aeolian transport process: The movement of sand and silt size sediment by the wind. Alluvium: A general term for any deposit (typically clay, silt, and sand sized fractions) that is laid down by a stream (channelized flow). Amplitude: The height of a wave measured from the crest to the trough. Area: A measure of the size within a two-dimensional polygon. Ash: A fine textured airborne material ejected from a volcanic eruption, transported by the wind, and ultimately deposited by gravity or the wind. Aspect: The direction a slope faces based on the azimuth or bearing system of angular measurement. Asthenosphere: The plastic to semi-liquid zone sandwiched within the upper mantle of the Earth. Atmosphere: The gaseous layer enveloping the Earth where energy exchanges result in weather and climate. Atmospheric window: The wavelength range within which the atmosphere can transmit electromagnetic radiation. AVIrIS: Airborne Visible/Infrared Imaging Spectrometer. A hyperspectral scanning system developed by the Jet Propulsion Laboratory (JPL) which captures 224 bands with a 10 nanometer band width in a range of 0.4 to 2.5 M. Azimuth: A method of measuring direction. Since the earth is spherical (oblate spheroid) in shape, directions are represented in angular measurements. An azimuth of north is zero degrees. Directions are measured clockwise from north with east having an azimuth of ninety degrees, south one-hundred eighty degrees, and west two-hundred-seventy degrees. All cardinal compass points are further represented in increments of degrees, minutes, and seconds for greater precision. There are sixty minutes in one minute, and sixty minutes in one degree. Band; The range of wavelengths representing a subset of the electromagnetic spectrum (e.g. the blue band). Basin/watershed: The total area that contributes water to a trunk stream (main channel) plus the entire network of smaller channels that connect and flow into it. Biomass: A biological energy source derived from living or recently living organisms. Biosphere: A system of energy exchanges within the life zone of the total Earth/Sun system. Breach: To break through such as a breach in a dam. Caldera: A collapsed crater formed when magma recedes down into the lower crust causing the floor to collapse due to a lack of support over an empty chamber.

2 Catastrophic event: An incident that results in a massive displacement of Earth materials due to a sudden release of energy. Chlorophyll: The green chemical compound (pigment) found in living plant tissue. Climate: The local, regional, and global trends in temperature, humidity, air pressure, precipitation, and atmospheric circulation patterns measured and recorded throughout time. Colluvium: A general term for loose rock material that has weathered from higher elevations and tends to collect at the base of slopes due to gravity. Composite image: A picture composed of three spectral bands in which each band is assigned one of the three primary colors (red, green, and blue). A natural color composite would consist of the red, green, and blue spectral bands each assigned their respective color. A false color composite would consist of three bands in which one or more would be outside the visible range of the electromagnetic spectrum; yet they would be each be assigned one of the three primary colors. In a typical false color (near infrared band included) composite, vegetation would appear red instead of green. Compression: A force that squeezes two or more objects together. Concave slope: An inclined surface that starts out steep from the top, then gradually levels out so that the profile (side view) would appear as a curve with the open side facing skyward. Continental margin: The transition zone that separates the continental crust from oceanic crust. Contour interval: The change in elevation between two adjacent contour lines. Contour line: A line that is of equal value along its entire extent. An elevation contour of 1,000 feet would eventually close forming a flat polygon surface 1,000 feet above mean sea level. Convergent plate boundary: A contact surface between two plates that are coming together. Convex slope: An inclined surface the starts out as a gradual grade from the top, then gradually steepen so that the profile (side view) would appear as a curve with the closed side facing skyward. Correlation: A systematic connection between multiple phenomena. An increase in temperature will result in an increase in pressure within a closed container. This is referred to as a positive correlation since there is an increase in both variables (temperature and pressure). Crater: An opening (depression) formed when a large volume of Earth material is displaced by a volcanic eruption. An impact crater can also form when a flying object such as a meteorite crashes into the Earth’s surface displacing Earth material also creating a large depression by contact. Crystal: A compound that has its atoms, ions, or molecules arranged in an orderly and repetitive geometric pattern forming a three dimensional solid. Cubic mile: A volume of material measuring one mile wide by one mile long by one mile high. Datum (sea level): A standard base level elevation computed as an average of tidal fluctuations for a particular region. A sea level datum varies around the planet due to world tidal fluctuations and sea floor topography; however, each datum represents a base level elevation of zero from which regional elevations above or below this mark are derived.

3 Debris avalanche: A mass movement of any mix of Earth materials that fall, slide, roll, or bounce down slope. Density: The mass per unit volume. Density is a measure of the amount of matter within a container. Increasing the pressure will always increase density of a material. Increasing temperature generally decreases density within a material. Digital elevation model: A computer file consisting of elevation values and locations assigned to a raster grid forming a pseudo-three dimensional image. Digital number: A value assigned to a pixel in a digital image. Discharge: The volume of fluid passing through a cross section in a unit of time generally measured in cubic feet or cubic meters per second. Divergent plate boundary: A rift (separation) zone resulting from forces that pull two plates apart creating an upwelling of magma from within the upper mantle. The magma spreads out from the rift creating new ocean crust. Dome: Geologically speaking, a dome is a rise in the Earth's crust due to an internal force often driven by the upward (surface) movement of magma. Domes are characteristically round to elliptical in shape, and initially possess relief such that they are topographically higher than the surrounding area. Over time differential weathering can erode the dome structure to the shape of a topographic basin. Drainage pattern: The geometric configuration (pattern) of all the streams in a drainage basin/watershed. Driving force: An agent that results in a change in motion of a free body, or causing stress in a fixed body. Dynamic: Processes that result in a change in the volume, shape, or position of matter throughout time. Earthquake: A sudden release of stored energy measured as seismic waves (vibratory energy) travel through the Earth’s crust. Earthquakes are often associated with slippage along plate boundaries. Ecology: A science concerned with the interaction between organisms and their interactions with the natural environment. Elastic: A physical property in which deformation occurs as a force is applied to an object; and when the force is released, the object returns to its original shape. Electromagnetic energy: Energy traveling at the speed of light in a harmonic wave pattern. Electromagnetic radiation: Energy reproduced in the form of an advancing interaction between electric and magnetic fields. Electromagnetic spectrum: The range of all possible frequencies and wavelengths of electromagnetic radiation. The visible range of the spectrum is the range that humans are capable of sensing with an unaided eye. Other spectral ranges beyond the visible are employed in satellite and airborne remote sensing applications. Element: A basic substance for all matter. An element chemically consists of a substance with one type of atom distinguished by its atomic number which is the number of protons in the nucleus.

4 Elevation: The height above or below a mean sea level datum. Emission: An ability of a body to radiate electromagnetic energy determined by kinetic temperature and emissivity. Emissivity: A ratio of radiant flux from a body to that from a black body at the same kinetic temperature. Energy: A measure of the ability to do work from a force. Forms of energy include: kinetic, potential, thermal, gravitational, sound, light, elastic, and electromagnetic. Erosion: The removal of weathered Earth materials by one or more transport agents. Event: An observable occurrence or noteworthy activity. Fallout: A release of particulates (typically clay, silt, or sand sized fractions) previously suspended in the atmosphere. Fallout occurs when an upward force is overcome by the gravitational force and solid Earth materials fall to the surface. False color composite image: A colorized image that is assigned one or more of the three primary reflective colors (red, green, and blue) to one or more spectral bands beyond the visible range of the spectrum. Fault: A fracture in Earth materials that shows evidence of movement (displacement). Felsic rocks: Rocks (generally igneous class) that contain a large proportion of the minerals silica and feldspar. Fissure eruption: Volcanic activity along rifts (divergent plate boundaries) and major fractures (fissures) on both continents and the sea floor. Flow path: The direction a fluid will move in response to gravity. Fluid: A substance that will continually deform under shear (a sliding force) stress. Fluids are a subset of phases of matter including liquids, gases, and plasma. A fluid has the ability to take the shape of a container. A liquid is the only fluid capable of forming a free surface (a surface not created by a container). All gases are fluids, but not all liquids qualify if there is gas within the liquid. Fluvial transport process: An ability of water flowing within an open channel to suspend, roll, slide, or bounce varied size particles downstream. Force: An agent that results in the change in motion of a free body, or causing stress in a fixed body. It may also be described as a push (compression), pull (tension), or twist (torque) causing a mass to change velocity. Force has magnitude and direction which makes it a vector. Fracture: A break in Earth materials. Gas: A fluid capable of taking on the shape of its container. Near absolute zero (0 degrees Kelvin) a substance exists as a solid. When heated to its melting point it changes to a liquid state. With continued heating to the boiling point liquids evaporate to a gaseous state. The difference between a liquid and gas is also a function of the vast separation of individual atoms when a substance is in a gaseous state. Geographic information system (GIS): A geographic information system (GIS) is fundamentally a functional assortment of software that interfaces with a computer for the purpose of addressing spatial issues. The term geographic can be broken down into two basic elements: geo is Earth-related, and graphic means to describe or depict the Earth through maps

5 or drawings. Information is data with explanation; or data in an applied sense. Information can be word-based or graphic and it is derived from data elements through a process of thought, observations, and measurement. Data consist of measured phenomena, statistics, or other quantitatively derived values. A system is a number of connected components or activities which, when linked together, interact as a functional unit. A GIS provides the platform to most effectively perform spatial analysis that can ultimately lead to an understanding for relationships, interactions, and processes within and between physical (e.g. soil, rock, plants, water, etc.) and social/cultural/economic (e.g. humans and their activities) elements found on Earth. A GIS can serve as an instrument used in decision-making, solving spatial problems, or support planning for the future (e.g. urban-regional planning, Earth resources planning, environmental planning). Geography: A spatial discipline that seeks to link, understand, and explain associations and inter-relationships of phenomena expressed by similarity, difference, or uniqueness of physical and human dimensions operating in areas or places on the planet. Geography organizes and integrates diverse knowledge to understand relationships between features found in and between places, as well as determine processes that operate to create those relationships. Geography is often thought of as an integrative discipline that brings together a study of relationships among people, places, and the natural environment from an area or spatial perspective. Geology: A study of the solid Earth; its composition, structure, history, and processes affecting a change in its size, shape, and composition. Geomorphology: Geo = Earth; morphology = shape or form. Geomorphology is a subdivision of the Earth sciences that focuses on processes (deposition and erosion of surface and subsurface material) affecting change on the Earth’s surface. Geospatial analysis: Geospatial analysis incorporates a multidisciplinary approach through the use of geographic information systems (GIS), remote sensing (digital image processing and traditional visual image interpretation), global positioning systems (GPS), and computer-assisted cartography. Geospatial: Investigative techniques dealing with location, distance, direction, pattern, shape, size, and position of objects that take up space; and their intimate associations between and among themselves as they exist throughout the physical and human dimensions of the world. Geothermal energy: Geo = Earth; thermal = heat. Energy created by the radioactive decay of elements within the mantle which produces convective cells that transfer energy in the form of heat throughout the lithosphere. Geyser: A hot spring that discharges turbulent surges of super heated water and steam into the atmosphere. Surface water penetrates several miles into the crust and is heated under pressure by magma. As the heated water begins to rise, the boiling temperature is lowered and at some point near the surface it flashes into an eruption of super heated water and steam called a geyser. Glacial till: A mix of varied sized deposits left behind from melting and receding glaciers. Glacial transport process: An ability of ice to deform and flow as a plastic medium. Rock and debris are trapped within the ice and act as dynamic sandpaper gouging and scouring the surface

6 as a glacier flows down a valley or spreads out from center mass on a continent or large land surface. Graben: The depressed (lower) block that is bordered by a higher block (graben) on each side. Tensional (pulling apart) forces fracture the crust. When these forces are relaxed, a center block drops down displacing the two adjacent higher (horst) blocks. Groundwater: Water that flows or is stored beneath the surface of the Earth. Horst: The higher elevation blocks that border a graben (see graben). Hot spot: Regions that occur when streams of magma rise from the upper mantle ultimately breaking (breaching) through the floor of an ocean plate as it travels over the magma plume (a column of magma rising into the crust). Hot spots can also occur on continents as a continental plate passes over a magma plume. Hot spring: Heated water that discharges through an opening on land, or through the floor of a lake or ocean under natural (not a result on any interaction by humans) conditions. Hot springs are a good indicator that there is a magma chamber close to the surface. Hummocky topography: Irregular hills and depressions formed by a rapid deposit of Earth materials through mass movements (landslides, debris flows, avalanches, lahars, etc); or by the release of rocks and debris from a retreating glacier. Hydroelectric power: The movement of a large volume of water driving generators to create electricity. Hydrosphere: A system of energy exchanges throughout the aqueous (water) layer enveloping the Earth. World weather patterns and climate result when energy is exchanged across the boundaries of the atmosphere and hydrosphere. Hypothesis: An explanation or proposal suggesting a correlation (a systematic connection) between multiple phenomena. It is often the first estimated answer to a problem. Igneous rock: Rock formed from extreme heat often associated with magma and the melting and solidification (lithification) of preexisting rock material. Interfluve: The upland surface between two stream valleys. An interfluve drains water off its surface into adjacent stream valleys. Kinetic energy: The extra energy an object possesses as a result of its motion. Kinetic energy is a measure of the amount of work required to accelerate a body of a given mass from rest to its current velocity. Kinetic temperature: The internal temperature of an object measured by random molecular motion with a contact thermometer. Lahar: A slurry of volcanic deposits often mixed with melt water from glaciers, snow, and ice fields. A volcanic mud and debris flow. Landsat: The Landsat program consists of a suite of Earth-observing satellites managed by the National Aeronautics and Space Administration (NASA) and the United States Geological Survey (USGS). The purpose is to provide consistent global multispectral imagery of the planet for the study of Earth and environmental sciences. The Landsat program has recorded the most comprehensive archive of repetitive calibrated digital imagery of any global satellite agency in the world.

7 Landslide: A mass movement in which a large portion of a slope fails and slides down to a lower position establishing a new threshold of stability for the displaced mass of Earth material. Latitude/longitude: Also called the geographic grid. A means of establishing locations, distances, directions, and relative positions on the Earth through an intersecting set (grid lines) of arcs and circles spaced in measured units of degrees, minutes, and seconds. Latitudes trend east/west while longitudes trend north/south (pole to pole). Lava: The term for magma when it breaches the crust and flows out on to the surface either on land or the ocean floor. LiDAR: An acronym for Light Detection And Ranging. LiDAR is an optical remote sensing technology that measures the properties and range of scattered light to a distant target ultimately generating an image of terrain and other structures residing on the surface. Lithosphere: A system of energy exchanges within the solid Earth. Littoral transport process: The movement of water and sediment along the land (continental)/ocean interface. Loess: Wind-blown deposit ranging from clay to very fine sand sized fractions, but predominately silt sized in composition. Loess is generally non-stratified (not layered) as a deposit. Mafic rocks: Rocks (generally igneous class) that contain a large proportion of magnesium and iron. Magma: Fluid rock that is created in the upper mantle due to the radioactive decay of existing Earth materials. Magnitude: An absolute or relative size, extent, or importance of something. In geology magnitude is a measure of the amount of energy released by an Earthquake. Mantle: The viscous layer between the crust and outer core of the Earth (2,970 km/1,800 mi thick). The mantle is approximately 84 percent of the Earth’s volume. The upper mantle is the source region where melting and the creation of magma occur. Mass movement: A large scale movement of Earth materials such as a fall, slide, flow, or roll. Mass: A measure of the amount of matter in an object. Mass differs from weight in that weight is a function of mass times the acceleration due to gravity. Since gravity differs on the Moon, weight would differ, while mass would remain constant. Metamorphic rock: Rocks that have been physically and chemically changed due to intense heat and pressure. Micrometer (micron): A length equal to one-millionth of a meter (1x10-6) or one-thousandth of a millimeter. Microwave: The wavelength range of the electromagnetic spectrum from 0.1 to 30 centimeters. Mineral: A naturally occurring (although we can reproduce some minerals under laboratory conditions), inorganic compound in solid form, with an orderly arrangement of atoms forming a unique geometric structure, and a specific chemical (elemental) composition. Molecule: An electronically neutral group of at least two atoms (elements) in a definite arrangement and chemically (covalent) bonded.

8 Mud pot: A slurry of water, volcanic ash, and clay minerals that erupts as hot mud. Mud pots are created by geothermal activity; and are associated with hot springs, fumaroles, and geysers. Nanometer: A length equal to one-billionth of a meter (1x10-9). Natural color composite image: A colorized image that is assigned the three primary reflective colors (red, green, and blue) to the three respective spectral bands (red, green, and blue). Natural environment: The entire physical realm of the Earth including the atmosphere, lithosphere, hydrosphere, biosphere and all energy exchanges driving the processes that promote change. Normalized difference vegetation index (NDVI): A measure of vegetation vigor computed as a ratio typically using the red and near infrared bands. Nutrient: A chemical substance necessary for an organism to live and grow. Panchromatic film: Film sensitive to the visible range of the electromagnetic spectrum, but displayed in gray tones. Pixel: An acronym for a picture element. The smallest spectral information in an image arranged in a two-dimensional grid and usually in the form of squares. Plane: A two dimensional surface. Planimetric area: Planimetric area is the geometric (flat plane) area. Changes in elevation are not taken into consideration. Plastic: A physical property in which deformation occurs as a force is applied to an object; and when the force is released, the object remains distorted in shape. Plate tectonics: A theory that explains the large scale movement of the asthenosphere (including continents) over the upper mantle. Plume: A geologic process associated with the upward movement of magma from the upper mantle. A plume may also be a collection of pollutants in a body of water or within the atmosphere. Pollutant: Any contaminant introduced into a natural system (streams, groundwater, lakes, oceans, atmosphere, etc.) that causes instability, disorder, harm, or discomfort to the natural order of the ecosystem. Precipitation: Any form of water generated within the atmosphere (rain, sleet, hail, snow, etc.) falling to the Earth’s surface. Pressure: A force per unit area directed perpendicular (at ninety degrees) to a surface or substance. Prevailing winds: The general direction from which wind (air) moves. A prevailing northeast wind would be interpreted as movement of air from northeast to southwest. Primary colors: In reflected light the additive primary colors are red, green, and blue. The subtractive primaries are yellow (red and green), cyan (green and blue), and magenta (red and blue). Process: Any action that results in a material change. Pyroclastic: Pyro = fire derived; clastic = rock fragment. Pyroclastics are generally associated with clay to silt to sand sized fractions of volcanically derived rock material, although they can be any size since their origin is a result of a volcanic eruption. Radiant flux: A rate of flow of electromagnetic radiation measured in watts per square centimeter.

9 Radiation: A process in which energy emitted (to give off) by a body travels through space or some medium and is ultimately absorbed by another body. Radioactive decay: A process in which an unstable atomic nucleus loses energy by emitting ionizing (positive or negative charged) particles and radiation. Recurrence interval: The time interval in which an event repeats itself. A discharge value from a hundred year flood would recur on average every one hundred years. Relief: Relief is the difference in elevation between two locations. Remote sensing: Remote Sensing is a science and technology concerned with viewing, identifying, and interpreting objects from a distance; hence the often used expression, sensing remotely. The manner in which objects are captured is through use of multispectral or hyperspectral scanning instruments/sensors housed within satellites orbiting above the Earth, or in aircraft sensors flying over areas of the Earth at lower altitudes. Most Earth resources satellite and airborne sensors collectively measure and store reflected (sun) light energy in the forms of visible, near-infrared, and longer forms of reflective infrared ranging in wavelength from 0.38 to 3.0 micrometers, as well as Earth emitted heat energy in wavelengths from 3.0 to 14.0 micrometers of the electromagnetic spectrum (EMS). Electromagnetic energy is collected from sunlight reflecting off the surface of Earth objects as well as collected as heat energy released (emitted) by Earth objects. Residuum: Weathered rock material that remains essentially in place. Residuum deposits are normally associated with chemical breakdown (weathering) with the residual material (residuum) left nearly in its original position (granite weathers into a residuum termed grus). Resisting force: A measure of stability. A resisting force prevents a sudden failure in an objects position that would result in movement. Rift valley: A long, linear depression formed when two plates are diverging (pulling apart). Rock structure: The geometric configuration of rock including: fractures, faults, folds, and inclined surfaces. Rock: A solid compound generally formed from two or more minerals. Scenario: A model description of an event or series of actions. Seamount: Mountain systems that were created below sea level. Seasonal thaw: Melting of ice and snow introducing runoff and filling of lakes, reservoirs, and groundwater system. Sediment: Any particulate matter than can be transported by a fluid, generally by water or the wind. Sedimentary rock: A rock class formed from sediment and other fragmented or chemically derived Earth materials. Sedimentary rocks are sub-classed as clastics when they develop from pre-existing fragmented rocks. Sedimentary rocks can also be derived from chemically dissolved compounds. Slope: The angle of inclination of a surface. Slurry: A thick, viscous suspension of solids in a liquid.

10 Solar radiation: Energy measured in wavelengths derived by the nuclear process of fusion in which hydrogen atoms are fused into helium. Solar energy is transmitted as electromagnetic wavelengths in all directions, and is the primary external energy source for the Earth. Spatial resolution: The smallest area that can be sensed by a scanning device. In digital imagery the length by height of a pixel represents the spatial resolution of an image (e.g. 10m by 10m). The more formal definition is the ability to distinguish an accurate measurement between closely spaced objects on an image. Spectral resolution: The range of wavelengths recorded by a sensing devise often called bandwidth. Spectrometer: An instrument used to measure intensity of radiation radiated or reflected by material as a function of wavelength. Spillover zone: A slope on Johnson Ridge that failed following the massive blast from the initial May 18th, 1980 eruption. Trees were uprooted and blown down leaving an exposed surface that later experienced a slope failure (landslide) due to a lack of stability. Storm runoff: Excess water that flows off a surface following a high intensity storm event. Stratosphere: The layer of the atmosphere above the troposphere characterized by layered warmer temperatures. Stream: A linear to curvilinear depression inclined to enable water to flow within its confines ultimately reaching a base level (another stream, lake, or the ocean). Subduction zone: The region formed as one plate is being forced (compression) below an adjacent plate along a convergent boundary. Summit: The highest point of a mountain. Super volcanic eruption: In order to qualify as a super volcanic eruption event, greater than 240 cubic miles (1,000 cubic kilometers) of Earth material must be ejected and or removed from the original volcanic structure (volcano). Supervised Classification: In a supervised classification a training sample of pixels is manually selected from a digital scene (image) to represent a specific Earth surface feature or feature class. The accuracy of the sample is based upon an analyst's ability to identify, interpret, and associate an assemblage of pixels having a unique digital range that represents the spectral characteristics for a particular Earth feature class (e.g. water, bare ground, deciduous trees, coniferous trees, etc.). A pixel by pixel classification is run on the entire scene to determine between class separations using the training samples in concert with a number of statistical models (algorithms). A supervised classification is used to fine tune the number of Earth feature classes based on the needs of an investigator and the spectral and statistical limits of a scene (image). The accuracy of any classification is ultimately based on statistical probability tests, and when distinct, homogeneous feature classes can be confidently associated and identified with actual derived field data. Surface area: Surface area is the total topographic area which considers changes in elevation. System: An assemblage of components which when assembled function as a single unit. Temperature: The degree of hotness or coldness of an object measured on a scale of Kelvin, Centigrade (Celsius), or Fahrenheit. Temporal: A measure of time.

11 Tension: A measure of force required to distort or fracture an object by pulling on it in opposing directions. Tephra: Any clastic material produced by a volcanic eruption regardless of the size or the composition of the fragments. Tidal fluctuation: A change in the height of sea level during a tidal event. Topographic map: A graphical representation of changes in the elevation of a land surface through the use of contour lines. Topography: Changes in the elevation, slope, aspect, and surface area of the Earth resulting in variations in the arrangement of surface expressions (landforms). Torque: A measure of force applied by twisting. Transform plate boundary: A plate boundary formed as two plates are sliding side to side past each other. The San Andreas Fault is created along a transform plate boundary. Transmissivity: A materials property that determines how much energy can pass through the material. Transport agents of erosion: The movement of eroded material by wind, water, and ice. The major transport agents include: aeolian, glacial, fluvial, and glacial. Tributary: A branch stream that enters into a higher order stream. The Wabash River is a tributary to the Ohio River. Tuff: Consolidated volcanic ash created as magma is blown apart while interacting violently with hot gases and steam during an explosive eruption. Ultramafic rocks: Igneous and meta-igneous rocks with greater than ninety percent mafic minerals (iron and magnesium) and a very low percentage of silica (less that forty-five percent). Ultramafic rocks are considered the principal rock type of the Earth’s mantle. Uniform slope: A slope that retains a constant angle along its entire length. As an inclined plane, the surface would be flat with no changes in angularity. Unsupervised Classification: In an unsupervised classification groups of pixels termed training samples or clusters are created by a statistical (clustering) algorithm. Each training sample represents a potentially discernible Earth surface feature class based upon its spectral characteristics (e.g. water, bare ground, deciduous trees, coniferous trees, etc.). Using these statistics, the complete range of spectral values within a scene is separated by assigning a specific range of brightness values to clusters that will ultimately represent Earth surface feature classes. In the early stages of image analysis, an unsupervised classification can provide valuable insight into the structure of the data with reference to the manner in which brightness values (spectral distinctions) are distributed throughout each spectral band. The informational utility of each class is next assessed based upon available ground truth, and interpretative expertise. The accuracy of any classification is ultimately based on statistical probability tests, and when distinct, homogeneous feature classes can be confidently associated and identified with actual derived field data. Vector: A straight line segment (length is its magnitude) with direction. Velocity: The rate of change of the position of an object in motion. Vertical slope: A slope at ninety degrees (perpendicular) to a horizontal plane.

12 Viscosity: The ability of a fluid to resist flow. Viscosity is lowered when a fluid is heated and increases when it is cooled. Visible light: A range of the electromagnetic spectrum (violet, blue, green, yellow, orange, red) ranging from 0.4 to 0.7 M. Volcanic vent: An initial opening that appears in the crust from the release of pressure as magma and gases force their way through the surface. Volcanism: A sudden release of stored energy (pressure) that expels gas, water vapor, lava, and pyroclasts into the atmosphere and onto the surface of the Earth. Volcanology: A science concerned with the study of geologic, geophysical, and geochemical processes and the energy exchanges (internal and external) that are directly responsible for volcanic activity. Volcanism and tectonics are intimately related processes. Volume: The amount of three dimensional (length by width by height) space any solid, liquid, gas, or plasma occupies. Wavelength: the length of a single wave measured from crest to crest of a wave. Weather: The physical condition of the atmosphere at any instance in time. Weathering process: The mechanical (physical) and chemical breakdown of matter, typically associated with Earth materials. Work: The amount of energy transferred by a force throughout a measured distance.