A Comprehensive Guide to Geological Processes and Landforms

Posted on May 13, 2024 in Geology

Geologic Cycle

Endogenic Processes

These are internal processes, such as plate tectonics and magma upwellings.

Exogenic Processes

These are external processes, such as wind, water, and erosion.

Igneous Rocks

Igneous rocks are formed from the cooling and solidification of molten rock material.

Magma

Magma is molten rock found beneath the Earth’s surface.

Lava

Lava is magma that has extruded onto the Earth’s surface.

Examples of Igneous Rocks

  • Granite
  • Basalt

Intrusive Igneous Rocks

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

  • Pluton (a large igneous intrusion covering over 100 square kilometers)
  • Batholith (a very large igneous intrusion)

Extrusive Igneous Rocks

Extrusive igneous rocks cool and solidify above the Earth’s surface. 90% of the Earth’s crust is composed of igneous rocks.

Jointing

Jointing refers to parallel cracks in rocks.

Exfoliation

Exfoliation is the process of rock peeling off in layers. An example of this is the formation of domes.

Sedimentary Rocks

Sedimentary rocks are formed from the accumulation and cementation of sediments.

Formation Process

  1. Weathering
  2. Compaction
  3. Cementation

Examples of Sedimentary Rocks

  • Limestone
  • Sandstone

Strata

Strata are layers of sedimentary rock.

Clastic Sediments

Clastic sediments are transported by water, wind, ice, or gravity.

Chemical Sediments

Chemical sediments are formed from minerals dissolved in solution.

Metamorphic Rocks

Metamorphic rocks are formed from the alteration of existing rocks due to heat and pressure.

Metamorphic Processes

  • Compression
  • Crushing
  • Heating
  • Shear and stress

Examples of Metamorphic Rocks

  • Marble
  • Gneiss
  • Slate

Foliated Texture

Foliated texture refers to the distinct wavy lines of minerals in metamorphic rocks.

Plate Tectonics

Plate tectonics is the theory that the Earth’s outer layer is made up of plates that move and interact with each other.

Continental Drift

Continental drift is the movement of the Earth’s continents relative to each other. This movement is caused by convection currents in the upper mantle, which move at a rate of about 6 cm per year.

Pangaea

Pangaea was a supercontinent that existed approximately 225 million years ago during the Triassic Period. It consisted of all the Earth’s landmasses.

Tectonic Processes

Tectonic processes refer to the building and deformation of the Earth’s crust.

Sea-Floor Spreading

Sea-floor spreading is the process by which new oceanic crust is formed at mid-ocean ridges. Magma rises from the mantle and solidifies, creating new crust. The youngest crust is found at the ridges, while the oldest crust is found farthest away, dating back approximately 208 million years.

Subduction Zones

Subduction zones are areas where one tectonic plate is forced beneath another. Continental crust, being lighter than oceanic crust, is driven underneath. The Mariana Trench near Guam, the deepest part of the ocean, is an example of a subduction zone, reaching a depth of 11,030 meters below sea level.

Plate Boundaries

There are three main types of plate boundaries:

  1. Divergent Boundaries: Plates move apart, creating new crust. An example is the Great Rift Valley in East Africa.
  2. Convergent Boundaries: Plates collide, resulting in the formation of mountains, volcanoes, and earthquakes. Examples include the Himalayas (continent-continent collision) and the Japanese archipelago (ocean-ocean collision).
  3. Transform Boundaries: Plates slide laterally past each other, without creating or destroying crust. An example is the San Andreas Fault in California.

Hot Spots

Hot spots are areas of upwelling magma from the mantle. They can be stationary or migrate over time. The Hawaiian-Emperor Islands chain is an example of a hot spot, with the oldest islands dating back approximately 80 million years.

Seamounts

Seamounts are underwater mountains formed by volcanic activity. The Ring of Fire in the Pacific Ocean is a zone of intense volcanic and earthquake activity associated with subduction zones. The Pacific Plate is being subducted beneath surrounding plates, creating numerous seamounts and volcanoes.

Volcanoes

Volcanoes are vents or conduits that allow magma to rise from the asthenosphere and upper mantle through the crust and onto the Earth’s surface. They play a significant role in shaping landforms.

Magma Chamber

Beneath the surface, a magma chamber collects magma before an eruption.

Crater

A crater is a round depression near the top of a volcano.

Volcanic Cones and Mountains

There are an estimated 1,300 to 1,500 volcanic cones and mountains on Earth. Around 500 to 600 are considered active, meaning they have erupted within the past 10,000 years. On average, 50 volcanoes erupt each year.

Volcanic Impacts

Over the past 30 years, volcanic eruptions have caused an estimated $3 billion in damage, required the evacuation of 800,000 people, and resulted in 29,000 deaths.

Lava

Lava is molten rock that flows from a volcano.

Pyroclastics

Pyroclastics, also known as tephra, are chunks of rock and other material ejected from a volcano during an eruption.

Aa Lava

Aa lava has a rough, jagged surface formed by the cracking of the thick lava skin.

Pahoehoe Lava

Pahoehoe lava has a smooth, rope-like surface.

Pele’s Hair

Pele’s hair is a type of volcanic glass formed from stretched lava.

Types of Volcanoes

  1. Cinder Cone: Small, short, cone-shaped hill formed from previous eruptions. Made of pyroclastic material and scoria.
  2. Caldera: Basin-shaped depression formed after the top of a volcano collapses. Often filled with water to become lakes.
  3. Flood Basalts (Plateau Basalts): Extensive, horizontal blankets of lava that spread over large areas. Lava erupts from fissures (linear vents).
  4. Shield Volcano: Resembles a knight’s shield lying face-down. Has a gentle and gradual slope, with a crater at the top. Formed from effusive eruptions.
  5. Composite Volcano (Stratovolcano): Massive, explosive eruptions create these volcanoes, which are characterized by alternating layers of ash, rock, and lava. They have a cone shape and steep slopes. Can be symmetrical if formed from a single eruption.

Volcanic Eruptions

There are two main types of volcanic eruptions:

  • Effusive Eruptions: Gentler eruptions with fluid, low-viscosity magma. Gases easily escape, resulting in few pyroclastics and small explosions.
  • Explosive Eruptions: More violent eruptions with high-viscosity magma. Gases are trapped, building pressure and leading to large amounts of pyroclastics and little lava flow. Examples include Kilauea in Hawaii and Mount St. Helens in Washington.

Volcanic Locations

Volcanoes are commonly found in:

  • Subduction zones (continent-oceanic, ocean-ocean)
  • Spreading zones (sea-floor spreading, continental rifts)
  • Hot spots

Earthquakes

Earthquakes are vibrations in the Earth’s crust caused by the sudden release of energy.

Types of Stress

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

Strain

Strain is the deformation of rocks under stress.

Folding

Folding occurs when rocks bend under stress. Ridges are the top peaks of folds, while troughs are the low valleys. An anticline is a fold where rock layers slope downward and away from the top, while a syncline is a fold where layers slope downward and inward towards the bottom. Plunges occur when the axis of a fold is not parallel to the surface. Overturned anticlines are folds that have been pushed together so much that they start to topple over.

Faulting

Faulting occurs when rocks break under stress. When a fracture occurs, energy is released quickly, causing an earthquake. There are three types of faults based on their tilt in relation to the fault plane:

  1. Normal Faults: Result from tension stress, where rocks are pulled apart. After fracture, one side moves vertically downward (hanging-wall side), while the other side moves upward (footwall side). Cliffs formed by normal faults are called fault scarps or escarpments.
  2. Thrust or Reverse Faults: Occur when rocks are pushed together under compression stress. In reverse faults, the hanging wall moves upward, hanging above the footwall side. This can result in landslides. If the fault plane is at a low angle, one block will slide on top of the other, creating a thrust fault. The 1994 Northridge earthquake in Los Angeles was caused by a thrust fault.
  3. Strike-Slip Faults: Occur when fault movement is horizontal due to shearing stress. They can be right-lateral or left-lateral. Strike-slip faults do not create cliffs but can form rift valleys. The San Andreas Fault is an example of a strike-slip fault.

Horst and Graben

  • Horst: Rock blocks that have faulted upward.
  • Graben: Rock blocks that have faulted downward.

Basin and Range Topography

Basin and range topography is characterized by abrupt relief and angular rock structures.

Bolson

A bolson is a low area between two ridges in a dry region. It has slopes and a basin.

Playas

Playas are salt crust areas left behind when evaporation occurs in a bolson or valley.

Orogenesis

Orogenesis is the process of mountain building. It involves the accumulation of materials, causing the crust to thicken, followed by uplift.

Seismic Waves

Seismic waves are vibrations that travel through the Earth during an earthquake. There are two main types:

  • Surface Waves: Travel along the top of the Earth’s crust.
  • Body Waves: Travel through the Earth’s interior. There are two types of body waves:
    • P-waves (Pressure Waves): Compressional waves that cause the rock or magma they travel through to vibrate parallel to the wave motion.
    • S-waves (Shear Waves): Cause rock to move at a 90-degree angle to the wave motion. S-waves cannot travel through liquids.

Earthquake Terminology

  • Focus (Hypocenter): The point below the Earth’s surface where an earthquake originates.
  • Epicenter: The point on the Earth’s surface directly above the focus.
  • Foreshock: Shaking that occurs before the main earthquake event.
  • Aftershock: Shaking that occurs after the main earthquake event, usually smaller in magnitude.

Richter Scale

The Richter scale measures the magnitude of an earthquake based on the amplitude of seismic waves.

Seismograph

A seismograph is an instrument that records vibrations in the Earth’s crust.

Landforms

Landforms are individual aspects of the Earth’s topography, such as mountains, valleys, hills, and caves. A landscape is a collection of landforms in one area. Geomorphology is the study of landforms.

Denudation

Denudation is the wearing away or removal of landforms by natural processes such as weathering, erosion, and mass movements.

Endogenic and Exogenic Processes

  • Endogenic Processes: Internal processes, such as tectonic uplift, create the initial landscape.
  • Exogenic Processes: External processes, such as weathering and erosion, work to wear down the landscape.

Destabilizing Events

Destabilizing events are physical events, such as fires, volcanic eruptions, or earthquakes, that disrupt the equilibrium of a landscape and create a new starting point for landform development.

Geomorphic Threshold

When the energy of a system exceeds the resistance of rocks, a geomorphic threshold or tipping point is reached. This leads to significant changes in the landscape.

Stages of Landform Development

  1. Equilibrium Stability
  2. Destabilizing Event
  3. Period of Adjustment
  4. New Equilibrium Stability

Erosion

Erosion is the process by which pieces of the Earth’s surface are transported away by natural agents such as water, glaciers, wind, and waves. Mass movements are large-scale erosion events.

Deposition

Deposition is the process by which eroded material is set down in a new location.

Differential Weathering

Differential weathering occurs when different rock types weather at different rates. Top rock layers can protect underlying layers from weathering.

Slopes

Slopes are curved, inclined surfaces. The convex upper part of a slope is called the waxing slope, while the concave lower part is called the waning slope.

Mechanical Weathering

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

  • Frost action
  • Salt-crystal growth
  • Pressure-release jointing

Blockfield

A blockfield is an area where rock pieces have collected due to weathering.

Talus

Talus is a steep slope formed by the accumulation of boulders that have fallen from higher elevations.

Chemical Weathering

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

  • Hydration
  • Hydrolysis
  • Oxidation
  • Carbonation

Biological Weathering

Biological weathering is the breakdown of rocks by living organisms. For example, lichen can extract nutrients from rocks, contributing to their weathering.

Angle of Repose

The angle of repose is the steepest angle at which a slope can remain stable.

Creep

Creep is the slow, downslope movement of soil and rock.

Solifluction

Solifluction is a type of mass movement that occurs in cold climates, where the ground repeatedly freezes and thaws.

Types of Mass Movements

  • Slide: Downward movement of a mass of rock or soil along a sloping surface.
  • Slump: A type of slide that rotates on a curved surface.
  • Flow: Fluid movement of material downslope. Examples include earthflows and debris flows.
  • Fall: Rapid, free-fall of rock or soil from a cliff or steep slope.

Groundwater

Groundwater is water found beneath the Earth’s surface.

Permeability

Permeability refers to the ability of a material to transmit water.

Infiltration

Infiltration is the downward movement of water into the soil.

Vadose Zone (Zone of Aeration)

The vadose zone is the layer of soil above the water table where both water and air are present in the pore spaces.

Phreatic Zone (Zone of Saturation)

The phreatic zone is the layer of soil below the water table where all pore spaces are filled with water.

Water Table

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

Aquifers

Aquifers are permeable layers of soil or rock that can store and transmit groundwater. Examples include sandstone and limestone.

Aquicludes

Aquicludes are impermeable layers of soil or rock that prevent the flow of groundwater.

Fluvial Processes

Fluvial processes are related to streams and rivers. Hydrology is the study of water and its movement.

Stream Orders

  • First-Order Streams: The smallest streams, also known as primary streams.
  • Second-Order Streams: Formed when two first-order streams combine.
  • Tertiary Streams: Formed when two second-order streams combine.

Types of Streams

  • Perennial Streams: Flow year-round.
  • Ephemeral Streams: Flow only during rainy seasons.
  • Intermittent Streams: Flow for some parts of the year.

Watershed (Drainage Basin)

A watershed, also known as a drainage basin, is the area of land that drains into a particular stream or river.

Drainage Divides

Drainage divides are boundaries that separate watersheds.

Drainage Patterns

  • Dendritic: Resembles the branching pattern of a tree.
  • Trellis: Resembles a vine growing on a trellis.
  • Radial: Streams flow outward from a central point.
  • Deranged: No clear pattern.

Sheetflow

Sheetflow occurs when water moves downslope in a thin sheet.

Rills

Rills are small indentations or cracks in the ground that collect water.

Gullies

Gullies are larger channels formed by the erosion of rills.

Amazon River

The Amazon River is the largest river in the world by discharge volume.

Discharge

Discharge is the amount of water that flows through a stream channel during a given time period. It is measured in cubic meters per second (m³/s) or cubic feet per second (ft³/s).

Discharge Formula

Q = wdv

Where:

  • Q = Discharge
  • w = Width of the channel
  • d = Depth of the channel
  • v = Velocity of the water

Fluvial Landforms

Fluvial landforms are created by the processes of erosion, transportation, and deposition by streams and rivers.

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

Base flow is the low discharge amount during dry seasons.

Peak Flow

Peak flow is the highest amount of discharge after a precipitation event.

Erosion by Streams

Erosion by streams depends on:

  • Turbulence: How rough the water flow is.
  • Abrasion: How rock particles in the water scrape along the sides and bottom of the channel.

Stream Load

  • Dissolved Load: Minerals dissolved in the water.
  • Suspended Load: Small particles that move within the water and settle to the bottom when the water flow slows down.
  • Bed Load: Larger pieces of rock and sediment that are rolled or bounced along the streambed.

Deposition by Streams

  • Aggradation: The process by which a stream channel is filled in by the deposition of eroded material.
  • Alluvium: Material that has been deposited by a stream. Alluvium is often fertile.
  • Alluvial Fans: Fan-shaped landforms created when an ephemeral stream empties out from a narrow canyon onto a flatter area.
  • Undercut Banks: Areas of high velocity in a stream channel where erosion is greater. Opposite undercut banks are point bar deposits, where sediment is deposited.
  • Oxbow Lake: A cut-off portion of a river that forms when a meander loop is bypassed.
  • Delta: A triangular-shaped deposit of alluvium that forms at the mouth of a river where it enters a larger body of water.
  • Floodplain: A flat, low-lying area adjacent to a river that is subject to flooding.
  • Levees: Barriers that run parallel to a river, formed by the deposition of sediment during floods.

Karst Topography

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