A Comprehensive Guide to Earth’s Dynamic Processes: From Geologic Cycles to Landform Development

Posted on May 29, 2024 in Geology

Geologic Cycle

Igneous Processes

Endogenic processes, such as plate tectonics and magma upwellings, originate from within the Earth. In contrast, exogenic processes, like wind and water erosion, operate externally.

Igneous rocks form from the cooling and solidification of molten rock material. Magma refers to molten rock beneath the Earth’s surface, while lava is magma that has erupted onto the surface. Common igneous rocks include granite and basalt.

Intrusive Igneous Rocks

Intrusive igneous rocks cool and solidify below the Earth’s surface. Examples include:

Plutons: Large igneous intrusions exceeding 100 square kilometers in size.
Batholiths: Massive plutons.

Extrusive Igneous Rocks

Extrusive igneous rocks form when lava erupts onto the surface. They constitute about 90% of the Earth’s crust.

Jointing and Exfoliation

Jointing: Parallel cracks that develop in rocks due to cooling, pressure release, or other stresses.
Exfoliation: The peeling away of rock layers in sheets, often resulting in dome-shaped formations.

Sedimentary Processes

Sedimentary rocks form from the accumulation and cementation of sediments, which are particles derived from the weathering and erosion of pre-existing rocks. This process involves weathering, compaction, and cementation. Examples include limestone and sandstone.

Strata and Sediment Types

Strata: Layers of sedimentary rock.
Clastic sediments: Transported by water, wind, ice, or gravity.
Chemical sediments: Formed from minerals precipitated from solution.

Metamorphic Processes

Metamorphic rocks form when existing rocks are altered by heat, pressure, or chemically active fluids. These processes can lead to changes in the rock’s texture, mineralogy, and overall appearance. Examples include marble (from limestone), gneiss (from granite), and slate (from shale).

Foliation

Foliated metamorphic rocks exhibit a distinct wavy or layered appearance due to the alignment of mineral grains under pressure.

Plate Tectonics

Plate tectonics is the theory that the Earth’s outer shell is divided into several plates that move and interact with each other. This movement is driven by convection currents in the Earth’s mantle, moving at a rate of about 6 centimeters per year.

Pangaea

Pangaea was a supercontinent that existed about 225 million years ago, during the Triassic Period, when all of Earth’s landmasses were joined together.

Sea-Floor Spreading

Sea-floor spreading occurs at mid-ocean ridges, where magma rises from the mantle and creates new oceanic crust. The youngest crust is found at the ridges, while the oldest crust is farthest away, with an age of up to 208 million years.

Subduction Zones

Subduction zones are areas where oceanic plates collide with continental plates. Because oceanic crust is denser, it is forced beneath the continental crust in a process called subduction. The Mariana Trench, near Guam, is the deepest part of the ocean, reaching over 11,030 meters below sea level, formed by subduction.

Plate Boundaries

There are three main types of plate boundaries:

Divergent boundaries: Plates move apart, creating new crust. An example is the Great Rift Valley in East Africa.
Convergent boundaries: Plates collide, resulting in subduction, mountain building, or volcanic activity. The 2011 Japan earthquake was caused by the convergence of the Pacific Plate and the Eurasian Plate.
Transform boundaries: Plates slide laterally past each other, neither creating nor destroying crust. The San Andreas Fault in California is an example.

Hot Spots

Hot spots are areas of volcanic activity caused by upwelling magma plumes from deep within the mantle. These plumes can remain stationary while plates move over them, creating chains of volcanoes like the Hawaiian-Emperor Islands chain, which has been forming for over 80 million years.

Seamounts

Seamounts are underwater mountains formed by volcanic activity. The Ring of Fire, a zone of intense volcanic and earthquake activity around the Pacific Ocean, is marked by numerous seamounts and volcanoes. This activity is primarily due to the subduction of the Pacific Plate beneath surrounding plates.

Volcanoes

Volcanoes are vents or fissures in the Earth’s crust that allow molten rock, ash, and gases to escape from the asthenosphere and upper mantle. They play a significant role in shaping Earth’s surface.

Volcanic Landforms

Craters: Round depressions near the summit of a volcano.
Calderas: Large, basin-shaped depressions formed by the collapse of a volcano’s summit after a massive eruption. They can often fill with water to become lakes.
Flood basalts (plateau basalts): Extensive, flat lava flows that cover vast areas. They originate from fissures, linear volcanic vents.
Shield volcanoes: Broad, gently sloping volcanoes resembling a warrior’s shield. They are formed by effusive eruptions of fluid lava.
Composite volcanoes (stratovolcanoes): Steep-sided, cone-shaped volcanoes built up by alternating layers of lava flows and pyroclastic material. They are associated with explosive eruptions.

Volcanic Eruptions

Effusive eruptions: Characterized by relatively gentle outpourings of fluid lava with low viscosity, allowing gases to escape easily. They produce few pyroclastics and result in less explosive activity.
Explosive eruptions: Occur when magma has a higher viscosity, trapping gases and building pressure. They are characterized by violent explosions, large pyroclastic flows, and the ejection of significant amounts of ash and volcanic debris. Examples include the eruptions of Kilauea in Hawaii and Mount St. Helens in Washington state.

Volcanic Distribution

Volcanoes are commonly found in these tectonic settings:

Subduction zones (continental-oceanic, oceanic-oceanic)
Spreading zones (mid-ocean ridges, continental rifts)
Hot spots

Earthquakes

Earthquakes are caused by the sudden release of energy in the Earth’s crust, resulting in seismic waves that shake the ground. They are often associated with tectonic plate boundaries and faults.

Tectonic Stress

Tension: Stretching of rock strata, leading to thinning of the crust and the formation of normal faults.
Compression: Shortening of the crust, resulting in folding and the formation of reverse faults.
Shear: Twisting or tearing motion, causing the crust to bend and form strike-slip faults.

Folding

Folding occurs when rocks are subjected to compressional stress, causing them to bend. Ridges are the upward folds, while troughs are the downward folds.

Types of Folds

Anticline: A fold that arches upward, with the oldest rocks at the core.
Syncline: A fold that arches downward, with the youngest rocks at the core.
Plunging fold: A fold whose axis is tilted relative to the horizontal plane.
Overturned fold: A fold that has been tilted so far that the layers are overturned.

Faulting

Faulting occurs when rocks break under stress. The surface along which the rocks break is called the fault plane. The three main types of faults are:

Normal faults: Caused by tensional stress, where rocks are pulled apart. The hanging wall moves downward relative to the footwall. Fault scarps or escarpments are cliffs formed by normal faults.
Reverse faults: Caused by compressional stress, where rocks are pushed together. The hanging wall moves upward relative to the footwall. Thrust faults are low-angle reverse faults. The 1994 Northridge earthquake in Los Angeles was caused by a thrust fault.
Strike-slip faults: Caused by shearing stress, where rocks slide horizontally past each other. Movement can be right-lateral or left-lateral. Strike-slip faults do not create cliffs but can form rift valleys. The San Andreas Fault is a right-lateral strike-slip fault.

Fault-Related Landforms

Horst: An uplifted block of rock between two faults.
Graben: A down-dropped block of rock between two faults.
Basin and Range: A type of topography characterized by alternating horsts and grabens, resulting in abrupt relief and angular rock structures.
Bolson: A flat-bottomed valley or basin between mountain ranges in arid regions.
Playa: A dry lakebed found in deserts, often covered in salt deposits.

Orogenesis

Orogenesis is the process of mountain building. It involves the accumulation of sediments, thickening of the crust, and uplift.

Seismic Waves

Seismic waves are vibrations that travel through the Earth’s interior and along its surface during an earthquake. There are two main types:

Surface waves: Travel along the Earth’s surface and cause the most damage.
Body waves: Travel through the Earth’s interior.

Types of Body Waves

P-waves (primary waves): Compressional waves that travel fastest and can pass through solids, liquids, and gases.
S-waves (secondary waves): Shear waves that travel slower than P-waves and can only pass through solids.

Earthquake Terminology

Focus (hypocenter): The point within the Earth where an earthquake originates.
Epicenter: The point on the Earth’s surface directly above the focus.
Foreshock: A smaller earthquake that precedes a larger earthquake.
Aftershock: A smaller earthquake that follows a larger earthquake.

Earthquake Measurement

Richter scale: A logarithmic scale that measures the magnitude (energy released) of an earthquake.
Seismograph: An instrument that detects and records seismic waves.

Landforms and Geomorphology

Landforms and Landscapes

Landform: An individual element of the Earth’s topography, such as a mountain, valley, hill, or cave.
Landscape: An assemblage of landforms in a particular area.
Geomorphology: The study of landforms and the processes that shape them.

Denudation

Denudation is the wearing away and removal of landforms through processes such as weathering, erosion, and mass wasting.

Endogenic and Exogenic Processes

Endogenic processes: Internal forces that uplift and create landforms, such as tectonic activity and volcanism.
Exogenic processes: External forces that wear down and modify landforms, such as weathering, erosion, and mass wasting.

Geomorphic Threshold and Equilibrium

Geomorphic threshold: The point at which a landform or system is no longer stable and undergoes significant change.
Equilibrium: A state of balance between opposing forces.

Erosion and Deposition

Erosion: The process of transporting weathered material from one place to another.
Deposition: The process of dropping off eroded material in a new location.

Differential Weathering

Differential weathering occurs when different rock types weather at different rates, leading to the formation of varied landforms.

Slopes

Slope: A curved, inclined surface.
Waxing slope: The convex upper part of a slope.
Waning slope: The concave lower part of a slope.

Mechanical Weathering

Mechanical weathering is the physical breakdown of rocks into smaller pieces. Examples include:

Frost action: The expansion of freezing water in cracks.
Salt-crystal growth: The growth of salt crystals in cracks, exerting pressure.
Pressure release: The expansion of rocks when overlying pressure is removed.
Jointing: The formation of cracks in rocks due to various stresses.

Landforms Associated with Mechanical Weathering

Blockfield: An area covered in large, angular rock fragments.
Talus: A slope formed by the accumulation of rock fragments at the base of a cliff.

Chemical Weathering

Chemical weathering is the breakdown of rocks through chemical reactions. Examples include:

Hydration: The absorption of water by minerals.
Hydrolysis: The reaction of water with minerals to form new compounds.
Oxidation: The reaction of oxygen with minerals, often iron-bearing minerals, to form oxides.
Carbonation: The reaction of carbonic acid (formed from carbon dioxide and water) with rocks, particularly limestone.

Biological Weathering

Biological weathering is the breakdown of rocks by living organisms, such as plants, animals, and microorganisms. For example, lichens can extract nutrients from rocks, contributing to their weathering.

Mass Wasting

Mass wasting is the downslope movement of rock and soil under the influence of gravity. Factors influencing mass wasting include slope angle, water content, vegetation, and earthquakes.

Angle of Repose

The angle of repose is the steepest angle at which a material can remain stable without sliding.

Types of Mass Wasting

Creep: Slow, downslope movement of soil and regolith.
Solifluction: Slow, downslope movement of water-saturated soil in cold regions.
Slide: Rapid downslope movement of a cohesive mass of rock or soil along a well-defined surface.
Slump: A type of slide that occurs on a curved surface, resulting in a rotational movement.
Flow: Downslope movement of a fluidized mass of rock, soil, and water. Examples include earthflows and debris flows.
Fall: The free-fall of rock fragments from a cliff or steep slope.

Groundwater

Groundwater is water found beneath the Earth’s surface in the pores and fractures of rocks and soil.

Infiltration and Percolation

Infiltration: The process of water soaking into the ground.
Percolation: The downward movement of water through the soil and rock layers.

Vadose Zone and Phreatic Zone

Vadose zone (zone of aeration): The zone above the water table where soil pores contain both air and water.
Phreatic zone (zone of saturation): The zone below the water table where all soil pores are filled with water.

Water Table

The water table is the upper surface of the phreatic zone.

Aquifers and Aquicludes

Aquifer: A permeable layer of rock or sediment that can store and transmit groundwater. Examples include sandstone and limestone.
Aquiclude: An impermeable layer of rock or sediment that prevents the flow of groundwater.

Fluvial Processes and Landforms

Fluvial Systems

Fluvial: Related to rivers and streams.
Hydrology: The study of water and its movement.

Stream Orders

First-order streams: The smallest streams, with no tributaries.
Second-order streams: Formed by the confluence of two first-order streams.
Third-order streams: Formed by the confluence of two second-order streams, and so on.

Streamflow

Perennial streams: Flow year-round.
Ephemeral streams: Flow only during and immediately after rainfall.
Intermittent streams: Flow for part of the year.

Watersheds and Drainage Basins

Watershed (drainage basin): The area of land that drains into a particular stream or river.
Drainage divide: A ridge or highland that separates adjacent watersheds.

Drainage Patterns

Dendritic: A tree-like branching pattern.
Trellis: A rectangular pattern controlled by underlying rock structures.
Radial: Streams radiate outward from a central point, such as a volcano.
Deranged: An irregular pattern with no clear geometry.

Fluvial Processes

Sheetflow: Water flowing over the land surface in a thin, broad sheet.
Rills: Small channels carved by running water.
Gullies: Larger channels carved by running water.

Fluvial Discharge

Discharge is the volume of water flowing past a point in a stream channel per unit of time. It is calculated using the formula Q = wdv, where Q is discharge, w is channel width, d is channel depth, and v is water velocity.

Fluvial Landforms

Fluvial landforms are shaped by erosion, transportation, and deposition by rivers and streams.

Base Level

Base level is the lowest elevation to which a stream can erode its channel.

Hydrograph

A hydrograph is a graph that shows the discharge of a stream over time.

Base Flow and Peak Flow

Base flow: The low discharge of a stream during dry periods, sustained by groundwater flow.
Peak flow: The highest discharge of a stream following a precipitation event.

Erosion

Stream erosion is influenced by factors such as turbulence (the roughness of the water flow) and abrasion (the scraping of rock particles carried by the water).

Stream Load

Dissolved load: Minerals dissolved in the water.
Suspended load: Small particles carried in suspension by the water flow.
Bed load: Larger particles that roll, slide, or bounce along the streambed.

Deposition

Aggradation is the process of stream channel filling by deposition of sediments.

Alluvium

Alluvium is sediment deposited by rivers and streams.

Fluvial Depositional Landforms

Alluvial fans: Fan-shaped deposits of sediment formed where a stream emerges from a narrow canyon onto a flatter surface.
Point bars: Crescent-shaped deposits of sediment on the inside of meander bends.
Oxbow lakes: U-shaped lakes formed when a meander loop is cut off from the main channel.
Deltas: Triangular-shaped deposits of sediment formed at the mouth of a river where it enters a lake or ocean.
Floodplains: Flat, low-lying areas adjacent to rivers that are subject to flooding.
Levees: Natural or artificial embankments along a river channel.

Karst Topography

(caves systems) carbonation=limestone interacts with water(chem weathering).