WorldWide Drilling Resource

WorldWide Drilling Resource ® is proud to work in cooperation with to bring you more information about the benefits of geothermal drilling. 37 WorldWide Drilling Resource ® OCTOBER 2013 Frequently-Used Geological Terms Part 24 Glossary Adapted from the Dictionary of Geological Terms G - Continued Geophone - An instrument for detect- ing vibrations passing through rocks, soil, or ice. Geopressured Aquifer - A term used for an aquifer, especially on the Gulf Coast, in which fluid pressure exceeds normal hydrostatic pressure. Geosphere - Any of the spheres or concentric layers of earth. Geosuture - A place where two conti- nents have come together. Geosyncline - A great downward flex- ing of the earth's crust. Geothermal - Refers to heat of the interior of earth. Geothermal Energy - Energy that can be extracted from earth’s interior heat. Geothermal Gradient - Rate of in- crease of temperature in earth with depth. Differs from place to place de- pending on heat flow in the region and thermal conductivity of rocks there. Geothermal Heat Flow - A measure- ment of the amount of heat energy leaving the earth. Geyser - A type of hot spring that occa- sionally erupts jets of water and steam, the result of groundwater coming into contact with rock hot enough to create steam under conditions preventing free circulation. Giant’s Kettle - Hole shaped like a cylinder, bored in bedrock beneath a glacier by water falling through a deep well or by boulders rotating in the bed of a meltwater stream. Glacial - Pertaining to an ice age or a region of glaciation. Glaciation - Formation, movement, and recession of glaciers or ice sheets. Glacier - Large mass of ice formed on land by compaction and recrystallization of snow, creeping downslope or outward due to stress of its own weight, and sur- viving year to year. Glacier Flood - Sudden release of meltwater from a glacier or glacier- dammed lake. Glacier Milk - Stream of turbid, whitish meltwater containing finely powdered particles of rock in suspension. Glaciology - Study of all aspects of snow and ice; the science of all process- es associated with solid existing water. G Layer - Seismic region of the earth’s interior below 3206 miles; the inner core. Gneiss - Layered metamorphic rock made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals. Goniometer - An instrument for meas- uring the angles between crystal faces. Gorge - A narrow, deep valley with nearly vertical rocky walls. Grab Sample - Sample of rock or sed- iment taken at any place. Gradient - Degree of inclination of a part of the earth’s surface; steepness of slope. May be expressed as a ratio, fraction, percentage, or angle. Granule - A rock fragment larger than a very coarse sand grain and smaller than a pebble. Gravity Survey - Measurements of the gravitational field at a series of different locations. Groin - A low, narrow jetty constructed Vertical geophone in use. Courtesy of the University of Texas. of timber, stone, concrete, or steel, usu- ally extending roughly perpendicular to the shoreline, designed to protect the shore from erosion by currents, tides, or waves, or to trap sand for the purpose of building up or making a beach. Grotto - A small cave, or one of the rooms of a cave. Next month, we will begin the letter H.