Glossary

Schist

Fact Sheet:

Chemical Composition: Primarily composed of mica (muscovite, biotite), quartz, feldspar, and other minerals depending on the type (e.g., garnet, chlorite, talc)
Hardness: Varies depending on mineral composition, typically 3 to 5 on the Mohs scale
Crystal System: Metamorphic rock, foliated (layered)
Color Varieties: Gray, brown, black, silver, green, and sometimes reddish depending on mineral content
Major Localities: United States, Canada, Scotland, Switzerland, India, and Brazil
Common Uses: Construction material, decorative stone, gemstone source, and geological research

Introduction: Schist is a highly foliated, coarse-grained metamorphic rock known for its abundant platy or flaky minerals, particularly micas ...

^EEarthquake

An earthquake is the sudden release of energy in the Earth’s crust that creates seismic waves, often due to the movement along a fault line. Earthquakes can cause significant ground shaking, leading to structural damage, landslides, tsunamis, and other hazards. Understanding earthquakes is essential in seismology, disaster preparedness, and the study of plate tectonics.

Reference: Scholz, C. H. (2002). “The Mechanics of Earthquakes and Faulting.” Cambridge University Press.

^EEddy Current

An eddy current is a circular movement of fluid, such as air or water, that flows in a direction contrary to the main current. Eddy currents are common in rivers, oceans, and the atmosphere, and they play a significant role in the transport of sediments, nutrients, and pollutants. Understanding eddy currents is important in oceanography, atmospheric science, and sedimentology.

Reference: Mann, J., & Ott, S. (1994). “Horizontal Coherence of Eddies in the Surface Layer.” Boundary-Layer Meteorology, 70(1-2), 183-205.

^EElastic Rebound Theory

Elastic rebound theory explains how energy is stored and released during an earthquake. According to this theory, stress builds up in the Earth’s crust as tectonic plates move, causing deformation. When the stress exceeds the strength of the rocks, they rupture, and the stored energy is released as seismic waves. This theory is fundamental in understanding the mechanics of earthquakes.

Reference: Reid, H. F. (1910). “The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation Commission.” Carnegie Institution of Washington.

^EElasticity (Geology)

Elasticity in geology refers to the property of rocks to deform under stress and return to their original shape when the stress is removed, as long as the stress does not exceed the material’s elastic limit. This concept is fundamental in understanding the behavior of rocks under tectonic forces, the propagation of seismic waves, and the mechanics of earthquakes.

Reference: Jaeger, J. C., Cook, N. G. W., & Zimmerman, R. W. (2007). “Fundamentals of Rock Mechanics.” Wiley-Blackwell.

^EEn Echelon

“En echelon” refers to a pattern of geological features, such as faults, folds, or veins, that are arranged in a staggered or overlapping configuration. This pattern is often indicative of shear stress and is important in structural geology for understanding the deformation of the Earth’s crust and the orientation of stress fields.

Reference: Cowan, D. S. (1999). “Structural Styles in Mylonitic Rocks of the Mecca Hills, Southern California.” Journal of Structural Geology, 21(9), 1285-1302.

^EEnd Moraine

An end moraine is a ridge of debris (till) deposited at the edge or terminus of a glacier. It forms when the glacier is stationary for a period, allowing the accumulation of sediments carried by the glacier. End moraines are key indicators of the past extent and dynamics of glaciers, and they provide valuable information about glacial advance and retreat cycles.

Reference: Benn, D. I., & Evans, D. J. A. (2010). “Glaciers and Glaciation.” Routledge.

^EEndorheic Basin

An endorheic basin is a closed drainage basin where water does not drain into the ocean but instead accumulates in a central lake or evaporates. These basins are often found in arid regions and are characterized by high salinity levels in their lakes due to evaporation. Endorheic basins are significant in hydrology, geology, and environmental studies of arid regions.

Reference: Deocampo, D. M. (2015). “Endorheic Basins.” In: Reference Module in Earth Systems and Environmental Sciences. Elsevier.

^EEnstatite

Enstatite is a common mineral in the pyroxene group, typically found in mafic and ultramafic igneous rocks, as well as in some metamorphic rocks. It is composed of magnesium silicate (MgSiO3) and is important in understanding the mineralogical composition of the Earth’s mantle and the petrogenesis of igneous rocks.

Reference: Deer, W. A., Howie, R. A., & Zussman, J. (2013). “An Introduction to the Rock-Forming Minerals.” The Mineralogical Society.

^EEolian Processes

Eolian processes involve the transportation, deposition, and erosion of sediments by wind. These processes are most active in arid and semi-arid environments, leading to the formation of dunes, loess deposits, and desert pavements. Eolian processes are critical in understanding desert landscapes, sediment transport mechanisms, and past climatic conditions.

Reference: Pye, K., & Tsoar, H. (2009). “Aeolian Sand and Sand Dunes.” Springer.

^EEpeiric Sea

An epeiric sea, also known as an epicontinental sea, is a shallow sea that extends over a large part of a continent, typically during periods of high sea levels. These seas are significant in paleogeography and sedimentology, as they are often associated with extensive sedimentary deposits and fossil-rich layers.

Reference: Johnson, M. E., & Boucot, A. J. (1996). “Paleogeography and Paleobiogeography: Biodiversity in Shallow Seas.” Geological Society of America Special Paper 306.

^EEpeirogenic Movement

Epeirogenic movement refers to broad, relatively slow, vertical movements of the Earth’s crust that result in the formation of large-scale features such as plateaus, basins, and continental interiors. Unlike orogenic movements, which are associated with mountain building, epeirogenic movements are typically not associated with significant folding or faulting.

Reference: Levandowski, W., & Jones, C. H. (2015). “Epeirogeny or Eustasy? Gauging Sea Level with Paleozoic Epeirogeny in the Central United States.” Geology, 43(2), 171-174.

^EEpeirogeny

Epeirogeny refers to broad, gentle uplifts or subsidence of large areas of the Earth’s crust, typically not associated with volcanic or seismic activity. These vertical movements can create plateaus, basins, and other large-scale landforms. Epeirogeny is important in understanding long-term landscape evolution, tectonics, and sedimentary basin development.

Reference: Bond, G. C. (1978). “Evidence for Continental Subsidence in North America During the Late Cretaceous Global Tectonics.” Geology, 6(11), 713-718.

^EEphemeral Gully

An ephemeral gully is a small, temporary channel formed by the concentration of runoff during heavy rainfall or snowmelt. These gullies can quickly erode and transport significant amounts of soil, contributing to landscape change and soil degradation. The study of ephemeral gullies is important in soil conservation, hydrology, and erosion control.

Reference: Poesen, J., Nachtergaele, J., Verstraeten, G., & Valentin, C. (2003). “Gully Erosion and Environmental Change: Importance and Research Needs.” Catena, 50(2-4), 91-133.

^EEphemeral Lake

An ephemeral lake is a temporary body of water that forms in arid or semi-arid regions, usually after heavy rainfall. These lakes exist for a short period before evaporating or draining away. Ephemeral lakes are significant in studying desert hydrology, sedimentation patterns, and the response of ecosystems to fluctuating water availability.

Reference: Yechieli, Y., & Wood, W. W. (2002). “Hydrology and Evolution of Saline Lakes in the Dead Sea Rift Valley.” Earth-Science Reviews, 58(3-4), 297-314.

^EEpicenter

The epicenter is the point on the Earth’s surface directly above the focus of an earthquake, where seismic waves are first generated. It is the location that typically experiences the strongest shaking during an earthquake. Understanding the epicenter is crucial in seismology for assessing the impact of earthquakes and for emergency response planning.

Reference: Lay, T., & Wallace, T. C. (1995). “Modern Global Seismology.” Academic Press.

^EEpiclastic

Epiclastic rocks are sedimentary rocks composed of clastic fragments derived from the erosion of pre-existing rocks, typically of volcanic origin. These rocks are important in reconstructing past volcanic environments and understanding the processes of erosion, transportation, and deposition in volcanic terrains.

Reference: Fisher, R. V., & Schmincke, H.-U. (1984). “Pyroclastic Rocks.” Springer.

^EEpigenesis

Epigenesis in geology refers to the process by which mineral deposits are formed or altered after the initial formation of the host rock, typically through the action of fluids. This process can lead to the introduction of new minerals or the alteration of existing ones, often resulting in economically valuable ore deposits. Epigenesis is important in economic geology and the exploration of mineral resources.

Reference: Guilbert, J. M., & Park, C. F. (1986). “The Geology of Ore Deposits.”

^EErosion

Erosion is the process by which soil, rock, and other surface materials are removed from one location and transported to another by natural agents such as water, wind, ice, or gravity. Erosion shapes landscapes, forms sedimentary deposits, and plays a critical role in the rock cycle and the formation of various geological features.

Reference: Montgomery, D. R. (2007). “Soil Erosion and Agricultural Sustainability.” Proceedings of the National Academy of Sciences, 104(33), 13268-13272.

^EErratic (Glacial)

A glacial erratic is a large boulder or rock fragment that has been transported and deposited by a glacier, often far from its original location. These rocks are typically different in composition from the bedrock on which they rest, serving as indicators of past glacial movement and ice sheet dynamics. Erratics are significant in studying the extent and direction of glaciation.

Reference: Benn, D. I., & Evans, D. J. A. (2010). “Glaciers and Glaciation.” Routledge.

^EEsker

An esker is a long, winding ridge of stratified sand and gravel deposited by meltwater streams flowing beneath a glacier. Eskers are significant features in glacial geomorphology, providing evidence of past glacial dynamics and meltwater processes. They are also important in hydrogeology as potential aquifers.

Reference: Shreve, R. L. (1985). “Eskers, Kames, and Subglacial Drainage Channels.” Geological Society of America Bulletin, 96(5), 639-646.

^EEustasy

Eustasy refers to global changes in sea level caused by variations in the volume of water in the oceans, typically due to the melting or formation of ice sheets and glaciers. Eustatic changes are crucial in understanding past climate change, sedimentary sequences, and the formation of coastal and marine landforms.

Reference: Miller, K. G., Fairbanks, R. G., & Mountain, G. S. (1987). “Tertiary Oxygen Isotope Synthesis, Sea Level History, and Continental Margin Erosion.” Paleoceanography, 2(1), 1-19.

^EEustatic Change

Eustatic change refers to global variations in sea level caused by changes in the volume of the world’s oceans, typically driven by the melting or growth of ice sheets and thermal expansion of seawater. Eustatic changes are crucial in understanding past climate changes, sea-level history, and the development of coastal environments.

Reference: Fairbanks, R. G. (1989). “A 17,000-Year Glacio-Eustatic Sea Level Record: Influence of Glacial Melting Rates on the Younger Dryas Event and Deep-Ocean Circulation.” Nature, 342(6250), 637-642.

^EEvaporite

Evaporites are sedimentary rocks formed by the precipitation of minerals from evaporating water, typically in closed basins in arid environments. Common evaporite minerals include halite (salt), gypsum, and anhydrite. Evaporites are important in the study of sedimentology, stratigraphy, and the economic extraction of minerals like salt and potash.

Reference: Warren, J. K. (2006). “Evaporites: Sediments, Resources, and Hydrocarbons.” Springer.

^WArchives: Glossary

A water budget is a balance sheet of water inflows, outflows, and storage changes within a specific system, such as a watershed, aquifer, or lake. The water budget is significant in hydrology and water resource management for understanding the availability of water resources, managing water supply, and assessing the impacts of land use and climate change on water systems.

Reference: Viessman, W., & Lewis, G. L. (2003). “Introduction to Hydrology.” Prentice Hall.