Choose a letter:

a   b   c   d   e   f   g   h   i   j   k   l   m   n   o   p   q   r   s   t   u   v   w   x   y   z

ice age	An interval of time in which the climate was colder than it is today, glaciers occasionally advanced to cover large areas of the continents, and mountain glaciers grew; can include many glacials and interglacials.
ice sheet	A vast glacier that covers the landscape.
ice shelf	A broad, flat region of ice along the edge of a continent formed where a continental glacier flowed into the sea.
ice stream	A portion of a glacier that travels much more quickly than adjacent portions of the glacier.
ice tongue	The portion of a valley glacier that has flowed out into the sea.
iceberg	A large block of ice that calves off the front of a glacier and drops into the sea.
icehouse period	A period of time when the Earth’s temperature was cooler than it is today and ice ages could occur.
ice-margin lake	A meltwater lake formed along the edge of a glacier.
ice-rafted sediment	Sediment carried out to sea by icebergs.
igneous rock	Rock that forms when hot molten rock (magma or lava) cools and freezes solid.
ignimbrite	Rock formed when deposits of pyroclactic flows solidify.
inactive fault	A fault that last moved in the distant past and probably won’t move again in the near future, yet is still recognizable because of displacement across the fault plane.
inactive sand	The sand along a coast that is buried beneath a layer of active sand and moves only during severe storms or not at all.
incised meander	A meander that lies at the bottom of a steep-walled canyon.
index minerals	Minerals that serve as good indicators of metamorphic grade.
induced seismicity	Seismic events caused by the actions of people (e.g. filling a reservoir, that lies over a fault, with water).
industrial minerals	Minerals that serve as the raw materials for manufacturing chemicals, concrete, and wallboard, among other products.
inequant	A term for a mineral grain whose length and width are not the same.
inertia	The tendency of an object at rest to remain at rest.
infiltrate	Seep down into.
injection well	A well in which a liquid is pumped down into the ground under pressure so that it passes from the well back into the pore space of the rock or regolith.
inner core	The inner section of the core 5,155 km deep to the Earth’s center at 6,371 km, and consisting of solid iron alloy.
inselberg	An isolated mountain or hill in a desert landscape created by progressive cliff retreat, so that the hill is surrounded by a pediment or an alluvial fan.
insolation	Exposure to the Sun’s rays.
interglacial	A period of time between two glaciations.
interior basin	A basin with no outlet to the sea.
interlocking texture	The texture of crystalline rocks in which mineral grains fit together like pieces of a jigsaw puzzle.
internal process	A process in the Earth System, such as plate motion, mountain building, or volcanism, ultimately caused by Earth’s internal heat.
intertidal zone	The area of coastal land across which the tide rises and falls.
intertropical convergence zone	The equatorial convergence zone in the atmosphere.
intraplate earthquakes	Earthquakes that occur away from plate boundaries.
intrusive contact	The boundary between country rock and an intrusive igneous rock.
intrusive igneous rock	Rock formed by the freezing of magma underground.
ionosphere	The interval of Earth’s atmosphere, at an elevation between 50 and 400 km, containing abundant positive ions.
iron catastrophe	The proposed event very early in Earth history when the Earth partly melted and molten iron sank to the center to form the core.
isobar	A line on a map along which the air has a specified pressure.
isograd	(1) A line on a pressure-temperature graph along which all points are taken to be at the same metamorphic grade; (2) A line on a map making the first appearance of a metamorphic index mineral.
isostasy (or isostatic equilibrium)	The condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down.
isostatic compensation	The process in which the surface of the crust slowly rises or falls to reestablish isostatic equilibrium after a geologic event changes the density or thickness of the lithosphere.
isotherm	Lines on a map or cross section along which the temperature is constant.
isotopes	Different versions of a given element that have the same atomic number but different atomic weights.