geomorphology topic 1 (part 2) - basic concept

Controlling Factors

Geomorphic Agents and Processes: Affect how rocks and sediment are eroded and transported.

Surficial Materials: Rocks and sediment of different types are located at the earth’s surface.

Tectonic Setting: Determines what materials are exposed at the earth’s surface and the manner in which they are distributed.

Climate: Determines what geologic agents are available to interact with exposed rock materials and influences the rate of physical and chemical reactions.

Climate

Determines what geologic agents are available to interact with exposed rock materials. Influences the rate of physical and chemical reactions.

• Combination of atmosphere and hydrosphere.• Driven by the Sun and modified by the earth’s rotation.• Responsible for storms, rivers, lakes, groundwater, sand dunes, glaciers, beaches, soil formation, oceanic currents, global circulation patterns, climatic belts, and anything thing else involving water or air.• Whereas, the tectonic system builds things up, the hydrologic system wears them down.• Primary processes include weathering, erosion, sediment transport, deposition, and lithification

Hydrologic System

From Okanagan University College, Department of Geography website

Photo by NASA

States of Matter

Matter exists in three forms (states) - solid, liquid, and gas. These represent the ability of atoms to vibrate and move about. The two primary controls are temperature and pressure. An increase in temperature adds energy, causing atoms to vibrate and move further apart, decreasing density. An increase in pressure forces atoms closer together, decreasing their ability to vibrate and increasing density.

Atoms are loosely packed and the substance conforms to the shape of its container.

Atoms are closely packed and the substance maintains its own shape.

From Hamblin & Christiansen (2001)

Atoms arecompletely separated and expand to fill all available space.

Energy Transfer

Most energy is transferred from one substance to another through three processes - conduction, convection, and radiation. This transfer can often be measured by changes in temperature.

Conduction: Energy is transferred by direct contact as the vibration of atoms on the surface of one material is transmitted to those on the surface of a neighboring material.

Convection: Energy is transferred as material moves from place to place due to differences in density, caused mostly by contrasts in temperature. When a material is heated, the atoms move farther apart, density decreases, and it rises. When the material is cooled, atoms move closer together, density increases, and it sinks.

Radiation: Energy is transferred through space by electromagnetic waves.

Global Water Distribution

Lakes, streams, ground water, and atmospheric water = 0.65%

Oceans = 97.2%Photo by W. W. Little

Ice = 2.15%

Photo by Global Marine Drilling

Photo by W. W. Little Photo by W. W. Little Photo by W. W. LittlePhoto by W. W. Little

The Sun

The Sun is the energy source driving the hydrologic system. Without the Sun, there is no hydrologic system.

Photo by NASA

Earth’s present atmosphere is distinctly different from that of its nearest neighbors, Venus and Mars; although, it is believed that earth’s early atmosphere was similar to that of its neighbors.

Atmospheric Compositions

Because of gravitational attraction, most of earth’s atmosphere is concentrated near the surface in the troposphere, causing both temperature and pressure to be higher at lower altitudes.

Atmospheric Pressure & Temperature

Climatic Belts & Temperature

Earth’s surface temperature is greatest at the equator, decreasing to a minimum at the poles.

Climatic Belts & Precipitation

The amount of precipitation that falls is strongly tied to latitude. It is highest at the equator, very low just north and south of the equator, moderate in mid-latitude regions, and lowest at the poles.

Because of earth’s spheroidal shape, a given amount of solar energy is spread over a larger area at the poles than along the equator.

Temperature and the Sun

Coriollis Effect

Earth’s rotation causes an atmospheric deflection that is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. This creates distinct belts of atmospheric circulation.

Surface RunoffStream channels are the most pervasive surface characteristic of earth’s continental masses. They are to earth what craters are to the moon.

Photo by NASA

Streams carry both water and sediment (boulders to dissolved ions) from the land to the sea, where the sediment is ultimately deposited.

Photo by W. K. Hamblin

Stream Deposition (deltas)

• Intensity and duration of rainfall.• Prior moisture content of surface material.• Porosity and permeability of surface material.• Gradient• Amount and type of vegetation.• Temperature

Runoff Controls

Surface runoff can be temporarily impounded by lakes and reservoirs.

Photo by W. K Hamblin

Lakes and Reservoirs

Glaciers represent a temporary disruption of normal surface runoff. Water is tied up in ice, which flows downhill in much the same manner as rivers but much more slowly.

Glaciers

Deserts

Deserts represent a disruption of the river system, which occurs when temperatures are sufficiently high so that the hydrologic system is partially shutoff due to a lack of precipitation. Eolian (wind) processes dominate and river systems can be completely overwhelmed by dune fields.

Photo by W. W. Little

Changing Environments

Radar images taken through dune fields of the Sahara Desert by the Space Shuttle reveal a well-developed drainage system.

Photos by NASA

Groundwater System

Some precipitation seeps into the ground and flows through the subsurface. It can return to the surface through seeps and springs or flow directly into streams, lakes, or the sea.

Groundwater dissolves rock and produces karst (dissolved) features, including sink holes and caves.

Karst Topography

Photo by W. W. Little

Landslides are typically caused by a high moisture content in surficial materials.

Landslides

• Waves: part of the hydrologic system driven by unequal solar heating (wind).• Tides: part of the hydrologic system driven by lunar gravitational attraction.• Submarine currents: part of the hydrologic system driven by water density contrasts (related to chemistry amd temperature) and earth’s rotation.

Shoreline SystemsRocks are eroded and sediment is transported along shorelines by waves, tides, and submarine currents.

Photo by W. W. Little

Seawater is mostly cold, but above freezing. However, a thin layer of warmer water exists at the surface, where it is heated by solar radiation. This is particularly evident at the equator.

Temperature of Seawater

As a result of the Coriollis Effect, ocean surface currents rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. These currents have important climatic implications.

Oceanic Surface Currents

Due to the Coriollis Effect, warm equatorial surface water is transported northward along the U.S. eastern coast and across the Atlantic Ocean toward Europe, affecting climatic conditions on both sides of the Atlantic.

Gulf Stream

Cold, highly saline polar water sinks and moves along the seafloor, then slowly moves upward where it mixes with warmer water of mid and low latitudes.

Deep Ocean Circulation

Oceanic circulation is very slow but over time involves mixing of the entire volume of the sea.

Whole Ocean Circulation

Controlling Factors

Geomorphic Agents and Processes: Affect how rocks and sediment are eroded and transported.

Surficial Materials: Rocks and sediment of different types are located at the earth’s surface.

Tectonic Setting: Determines what materials are exposed at the earth’s surface and the manner in which they are distributed.

Climate: Determines what geologic agents are available to interact with exposed rock materials and influences the rate of physical and chemical reactions.

Geomorphic Agents and Processes

• Atmospheric moisture (weathering)• Gravity (mass movement)• Running water (stream erosion, transport & deposition)• Groundwater (dissolution & precipitation)• Flowing ice (glacial erosion, transport & deposition)• Wind (eolian erosion, transport & deposition)• Waves (long-shore erosion, transport & deposition)• Tides (tidal erosion, transport & deposition)

Determine how the land is sculpted

Atmospheric Moisture

The amount of moisture in the air and its composition will control the type and degree of chemical weathering affecting material surfaces.

Gravity

Material loosened by weathering tends to be pulled down hill by gravity.

Running Water

Rivers can be thought of as conveyor belts that remove weathered materials and transport them to a depositional basin.

Groundwater

Groundwater can dissolve or precipitate minerals dependent upon temperature and pressure conditions, composition of the material through which the water is flowing, and the type and concentration of dissolved ions in solution.

Flowing Ice

Flowing ice represents a modification of surface runoff due to extremely cold temperatures. Glaciers are highly competent as an erosional agent and sediment transport mechanism and produce many distinctive landforms.

• Snow accumulates more rapidly than it melts.

• As snow reaches a sufficient thickness, it compresses to ice and begins to flow.

• Flowing ice scours the underlying bedrock producing a cirque.

• As the glacier grows, it extends further down the valley.

• Ultimately, a landscape of U-shaped and hanging valleys, horns, aretes, and other features is produced.

Alpine Glacial Valleys

Wind

Deserts represent a disruption of surface runoff due to a lack of precipitation. Wind is the least competent mechanism of sediment erosion and transport but is still responsible for the formation of many landforms.

Waves

Waves move sediment along the coast by means of longshore currents. They erode at headlands and deposit in bays, causing a smoothing and straightening of the shoreline.

Tides

Tides move sediment back and forth perpendicular to the coastline. They produce flat depositional surfaces characterized by rippled plains, marshes, and channels with irregular patterns.

Controlling Factors

Geomorphic Agents and Processes: Affect how rocks and sediment are eroded and transported.

Surficial Materials: Rocks and sediment of different types are located at the earth’s surface.

Tectonic Setting: Determines what materials are exposed at the earth’s surface and the manner in which they are distributed.

Climate: Determines what geologic agents are available to interact with exposed rock materials and influences the rate of physical and chemical reactions.

Surficial Materials

Geomorphic features are strongly influenced by the nature of materials exposed at the surface.

• Bedrock or sediment• Composition• Stratigraphy

Landscape Evolution

Landscapes evolve toward an equilibrium that reflects a balance between tectonic and hydrologic forces. When changes occur in one of these systems, the landscape adjusts to reflect those changes.

The Great Unconformity

Arizona Missouri

SoutheasternCanada

Concepts of EquilibriumEquilibrium means balance. In geomorphology, it refers to no net change, usually in terms of a balance between deposition and erosion, uplift and downcutting, or soil production and removal.

• Equilibrium is strived for but seldom achieved.

• A change in one part of a system affects all others.

Fluvial EquilibriumRecent uplift in excess of erosional rates results in a system that is out of equilibrium.

Weathering and erosion dominate headland areas with removed material being transported to a depositional basin.

As headlands recede, both erosional and depositional rates decrease.

If the region remains stable for an extended period, equilibrium, where erosional and depositional rates are equal, might be achieved.

• Sea level is the ultimate base level

• Lakes and reservoirs provide temporary base levels

• Changes in sea level can be eustatic or relative

• Changes in base level create and destroy accommodation space

Base LevelBase level is the level below which erosion cannot occur and above which deposition does not take place.

Graded (Longitudinal) Profile

Stream gradient is related to water velocity and the load it can transport. A change in any of these affects the other two. Each can be influenced by factors outside of the stream system, such as base level fluctuations (gradient), precipitation changes (discharge), and sediment character.

Coastal Equilibrium (Channel Mouths)

Deltas represent a “battle” between fluvial and marine (wave & tidal) processes. Delta morphologies are highly influenced by which of these processes dominates.

Coastal Equilibrium (headlands & bays)

Coastal processes work to straighten and smooth shorelines by focusing energy at headlands, with minimal energy within bays. Overall basin size and geometry, composition of coastal materials, and wind characteristics all play a role.

An open system is one in which both energy and matter cross its boundaries. A closed system allows only energy to enter or exit.

Open vs. Closed Systems

Open System Closed (nearly) System

Negative Feedback Systems

Negative feedback systems adjust internally to external forces.

Positive Feedback SystemsPositive feedback systems feed upon and ultimately eliminate themselves. External forces enhance (accelerate) internal processes.

System Complexity

Geological systems can be highly complex, with numerous interdependent variables, making modeling extremely difficult.