Geographic Glossary
Short, plain-language definitions for the terms used across the Frontline Earth library.
67 terms.
A
- A'a Lava
- A type of basaltic lava flow with a rough, jagged, spiny surface, formed when flowing lava cools and fractures as it moves.
- Abrasion
- The wearing away of rock surfaces by friction, as sediment carried by ice, water, or wind scrapes against bedrock.
- Alluvium
- Loose sediment — clay, silt, sand, or gravel — deposited by flowing water, typically in riverbeds, floodplains, and deltas.
- Aquifer
- An underground layer of permeable rock or sediment that holds and transmits groundwater.
- Arête
- A sharp, narrow mountain ridge formed when glaciers erode both sides of a mountain spine.
B
- Basalt
- A dark, fine-grained volcanic rock formed from rapidly cooled lava, rich in iron and magnesium.
- Bedrock
- The solid rock that lies beneath soil, sediment, and other loose surface material.
C
- Caldera
- A large, bowl-shaped depression that forms when a volcano's summit collapses after a major eruption empties the magma chamber below it.
- Calving
- The breaking away of chunks of ice from the edge of a glacier or ice shelf, often where it meets open water.
- Chemical Weathering
- The breakdown of rock through chemical reactions, such as the dissolving of limestone by slightly acidic water.
- Cirque
- A bowl-shaped hollow carved into a mountainside at the head of a glacier by rotational ice movement and erosion.
- Continental Crust
- The thicker, lower-density rock that makes up Earth's continents, distinct from the thinner oceanic crust.
- Convergent Boundary
- A location where two tectonic plates move toward each other, often producing mountains, volcanoes, or deep ocean trenches.
- Crater
- A bowl-shaped depression formed either by a volcanic eruption or by the impact of a meteorite.
- Crevasse
- A deep crack in a glacier's surface, formed as the ice moves and stretches over uneven terrain.
D
- Delta
- A landform built where a river deposits sediment as it slows down and spreads out, typically where it meets a sea, lake, or ocean.
- Deposition
- The process by which sediment carried by wind, water, or ice is laid down and accumulates in a new location.
- Dissolution
- The chemical process by which minerals, especially limestone, dissolve when exposed to slightly acidic water.
- Divergent Boundary
- A location where two tectonic plates move apart, allowing magma to rise and new crust to form, as in rift valleys and mid-ocean ridges.
- Drainage Basin
- The area of land where all surface water, from rainfall to streams, drains to a common river or outlet.
- Dune
- A mound or ridge of sand built up by wind, typically found in deserts and along coastlines.
E
- Erosion
- The wearing away and removal of rock, soil, or sediment by natural forces such as water, wind, or ice.
- Escarpment
- A steep slope or cliff that marks a sharp change in elevation, often separating two relatively flat areas.
- Evaporite
- A mineral deposit, such as salt or gypsum, left behind when a body of water evaporates.
F
- Fault
- A fracture in the Earth's crust along which blocks of rock have moved relative to one another.
- Floodplain
- The flat land bordering a river that is periodically covered by water during floods and built up by deposited sediment.
- Fumarole
- An opening in the Earth's surface that emits steam and volcanic gases, often found in geothermal areas.
G
- Glacial Till
- Unsorted sediment — a mix of clay, sand, gravel, and boulders — deposited directly by a glacier.
- Glacier
- A large, slow-moving mass of ice formed from accumulated snow that persists and flows under its own weight.
- Groundwater
- Water that exists beneath the Earth's surface in the cracks and pore spaces of soil and rock.
H
- Headward Erosion
- The gradual extension of a valley, gully, or stream channel upslope, toward its source, as erosion cuts further back.
- Hoodoo
- A tall, thin spire of rock left standing after surrounding softer rock has eroded away, common in badlands.
- Hot Spot
- A location where unusually hot material rises from deep within the mantle, producing volcanic activity independent of plate boundaries.
- Hydrothermal
- Relating to hot water, typically water heated underground by volcanic or geothermal activity.
I
- Igneous Rock
- Rock formed from the cooling and solidification of molten magma or lava.
- Isostasy
- The gravitational balance between the Earth's crust and the denser mantle beneath it, which causes crust to rise or sink as weight is added or removed.
K
- Karst
- A landscape shaped by the dissolution of soluble rock, usually limestone, producing caves, sinkholes, and underground drainage.
L
- Lava
- Molten rock that has reached the Earth's surface through a volcanic eruption.
- Levee
- A raised ridge of sediment along a riverbank, built naturally during floods or constructed artificially to contain water.
- Limestone
- A sedimentary rock composed mainly of calcium carbonate, often formed from marine organism remains and highly soluble in acidic water.
- Loess
- A fine, wind-blown silt deposit that forms fertile, easily eroded soil in some plains regions.
M
- Magma
- Molten rock found beneath the Earth's surface, which becomes lava once it erupts above ground.
- Magma Chamber
- A large underground pool of molten rock beneath a volcano that feeds eruptions.
- Mantle
- The thick layer of hot, slowly flowing rock between the Earth's crust and its core, whose movement drives plate tectonics.
- Meander
- A winding curve in a river channel, formed as flowing water erodes the outer bank and deposits sediment on the inner bank.
- Metamorphic Rock
- Rock that has been transformed by intense heat and pressure, without fully melting, changing its mineral structure.
- Moraine
- A ridge of rock debris deposited directly by a glacier, usually marking its former edge or extent.
O
- Oceanic Crust
- The thinner, denser rock layer that forms the floor of the oceans, distinct from continental crust.
- Orogeny
- The geological process of mountain building, typically driven by the collision or convergence of tectonic plates.
- Oxbow Lake
- A curved lake formed when a river meander is cut off from the main channel and left isolated.
P
- Permafrost
- Ground, including soil and rock, that remains frozen for at least two consecutive years.
- Plate Tectonics
- The scientific theory describing how Earth's rigid outer shell is divided into plates that move slowly over the mantle, shaping continents and ocean basins.
- Pyroclastic Flow
- A fast-moving, extremely hot current of volcanic gas, ash, and rock fragments that flows down a volcano's slopes during an eruption.
R
- Rift Valley
- A long, low-lying trough that forms where the Earth's crust is being pulled apart along a divergent boundary.
S
- Sediment
- Solid material — fragments of rock, mineral grains, or organic matter — that is transported and deposited by water, wind, or ice.
- Sedimentary Rock
- Rock formed from the compaction and cementation of accumulated sediment over time.
- Sinkhole
- A depression or hole in the ground caused by the collapse of a surface layer into an underground void, often in karst terrain.
- Stratovolcano
- A steep-sided, cone-shaped volcano built from alternating layers of hardened lava, ash, and volcanic rock.
- Subduction
- The process in which one tectonic plate is forced beneath another at a convergent boundary and sinks into the mantle.
T
- Talus
- An accumulation of broken rock fragments at the base of a cliff or steep slope, formed by repeated rockfall.
- Tectonic Plate
- One of the large, rigid sections of Earth's lithosphere that move slowly over the mantle below.
- Tributary
- A smaller stream or river that flows into a larger river rather than directly into a sea or lake.
U
- U-Shaped Valley
- A valley with steep, rounded sides and a flat floor, carved by the broad erosive action of a glacier.
V
- V-Shaped Valley
- A narrow valley with sloped sides that meet at a point, typically carved by a river cutting downward.
- Volcanic Arc
- A curved chain of volcanoes that forms above a subduction zone, parallel to a plate boundary.
W
- Water Table
- The upper surface of the saturated zone underground, below which all pore spaces are filled with water.
- Weathering
- The breakdown of rock in place, through physical, chemical, or biological processes, without the material being transported away.