Exogenic Processes

1. Rocks and Debris falls

Rock falls occur when a piece of rocks or a mass of rocks become dislodge and makes free-fall along a steep cliff. Debris fall is similar to rock fall, except that it involves a mixture of soil regolith, vegetation and rocks. At the base of the cliff in an accumulation of fallen materials called talus.

2. Landslides

Landslides are sudden fast movement of cohesive mass of soil, rock, or regolith. They occur in two types: Translation and Rotational slides. Translational slides involve the movement of a mass of materials along a well-defined surface, such as bedding plane, foliation surface, or joint surface. Rotational slides or slumps occur when the descending materials move en-masse along a concave, upward curved surface.

3. Flows

Flows may be slurry flows or granular flows. Slurry flows consists of mixtures of rocks or regolith with 20% to 40% of water. They are considered as water-saturated flows. Granular flows contain 0 to 20 % water. They are not saturated with water.

Slurry flows may be subdivided further on the based on velocity.

Although mass wasting is phenomenon, human activities may induce mass movement.

Running water is the primary agent of erosion on Earth. Most running water is found in streams and rivers.

There are different types of water erosion that affect landforms: Splash erosion, Sheet erosion, Gully erosion, Valley erosion, Bank erosion, Coastline erosion, Seaside cliff erosion.

• Splash Erosion- raindrops cause tiny particles of soil to be detached and to move out.
• Sheet Erosion- raindrops break apart the soil structure which moves down the slope as water flows overland as sheet.
• Gully Erosion- after heavy rain, water flows in narrow channels, eroding gullies into great depth.
• Valley Erosion- continuous water flows alongside land and move downward, which deepens a valley.

• Bank Erosion- continuous flow of water wears out stones along the bank of streams and rivers.
• Coastline Erosion- waves from ocean and seas crash against the shore, pounding the rocks into pebbles and reducing the pebbles to sand.
• Seaside Cliff Erosion- the battering of ocean waves erodes seaside cliffs, forming hales that create caves. Continuous pounding of waves may create an arch that may fall, leaving nothing but rock columns called sea stocks.

A glacier is a thick large mass of ice formed hundreds or thousands of years mostly in remote areas like in the poles or in high mountains. They move very slowly.

Plucking is the process wherein fractured bedrocks are incorporated into the ice. This occurs when ice water freezes. It expands, loosens, and pulls out the rocks fragments, becoming part of the glacier.

The abrasional effect happens when the ice and its load of rock fragments slide over a bedrock. Abrasion smoothens and polishes the surface below. The result of abrasion may be rock flour (pulverized rock) or glacial striation (scratches and grooves) on the bedrock surface.

5.2 Mass Wasting

Exogenic Processes

Types of Mass

wasting:

Mass Wasting is the mass movement of rocks, soil, and regolith. It is the step that follows weathering and is also a degradation process. The driving force of mass wasting is gravity. Although gravity is the controlling force, there are other factors that influence or trigger the down slope of anchoring vegetation and ground vibration of earthquakes.

Exogenic Processes

• External processes that occur at or near the surface of the earth.
• Part of the rock cycle
• Responsible for transforming rock into sediment.
• Includes degradation of processes (weathering, mass wasting, erosion, and transportation) and aggradation processes (deposition).

• Solifuction- the flow rate is around 1 cm/yr and occurs in areas saturated with water.
• Debris flows- the velocities range from 1m/yr to 100m/h; these result from heavy rains.

• Mudflows- these are high velocity mixtures of sediment and water. The velocities are greater than 1km/h; these result from heavy rain and can travel long distances.

Granular flows may be subdivided further based on velocity.

• Creep- the slow movement of regolith down a slope, observed in bent trees and fences.
• Earthflows- the velocities range from less than 1cm/yr to less than 100m/h

• Grain flows- the velocities range from 9 to 100m/h to less than 100m/h; they’re relatively dry materials like sand dunes.
• Debris avalanche- these are very high velocity flows(more than 100m/h) of large volume of mixtures of rocks and regolith.

Types of Mass wasting:

Human and Mass Wasting

• Vegetation helps hold soil, loos rocks, and regolith through the roots of plants.
• Oversteepening slopes may be due to quarrying, open-pit mining, home building on steep slopes, highway constructions(road cuts) and adding weight to slopes with housing construction.

• Adding moisture to slopes through lawn watering, leakage, and draining in swimming pool, and water reservoir leakage also induces mass movement. Water serves as lubricant in mass movement. Reducing water in a slope makes the slope more stable.

Types of Mass

wasting:

Mechanical Weathering

Frost wedging or Frost Weathering occurs in regions where temperature fluctuates above and below freezing point, resulting in a freeze-thaw cycle.

Water that enters through the cracks and empty spaces of rocks expands when it freezes. The ice exerts enormous outward force. When the ice thaws, water can flow further into the crack. Repeated freeze-thaw cycles weaken the rock and break up the rock into smaller pieces.

Mechanical Weathering or Disintegration is the breaking up of large rocks into smaller fragments without changing the rock’s mineral compositions.

There are physical processes that occur in nature break rocks into smaller pieces. It includes frost wedging, insolation weathring, unloading, and biological activity.

Unloading or Pressure Release occurs when the overlying rock is eroded away, causing the outer rock to expand more then the rock below. This expansion may separate the outer rock from the rock body. This process is evident in intrusive igneous rocks. Intrusive igneous rocks are formed deep beneath Earth’s surface. The overlying rock material exerts tremendous pressure on the igneous rock. When erosion removes the overlying materials, the presence on the igneous rocks is released, causing the outer portion to expand. Continued weathering causes sheets of rocks to break away. This exfoliation is due to the pressure released, often referred to as sheeting.

Insolation weathering or Thermal stress results from the expansion and contraction of rocks caused by temperature change. The coefficient of expansion differs for each mineral in the rock, resulting into different stress that may cause the rock to crack apart. Furthermore, the outer surface of the rock is warmer or colder than the inner portions, which may cause the peeling away of outer layers. The process of “peeling off” is called exfoliation.

Agents of Erosion

Chemical Weathering

• Oxidation- oxygen dissolved in water will oxidize some materials. Reddish-brown rust will appear on the surface of iron-rich minerals which easily crumbles and weakens the rock.
• Hydrolysis- water is perhaps the most important agent of chemical weathring. It affects silicate. For example, in the case of olivine, a silicate and water:

Olivine + Water  magnesium hydroxide + silicic acid in solution

*The reaction results in the dissolution of the original mineral.

5.1 Weathering

Agents of Erosion

Chemical Weathering decomposes rocks through chemical change.

The processes includes: Oxidation, Hydrolysis, Carbonation and solution, Biological Action.

Rates of Weathering

Rock characteristics include mineral composition, solubility and cracks. Variation in the composition of minerals in the rock results in differentiated weathering. Cracks are important because they influence the ability of water to seep through the rocks.

Climate, specifically, temperature and moisture, are two climatic factors are crucial to the rate of weathering. The freeze-thaw cycle, which is dependent on the temperature changes, affects the amount of frost wedging. The combination of warm temperature and abundant moisture is a very good environment for chemical weathering.

• Carbonation and Solution

Carbon dioxide dissolves in water to form carbonic acid and reacts with the carbonate rocks to form a soluble product (calcium bicarbonate).

• Biological actions

Some plants and animals may create chemical weathering by releasing chelating and audifying compounds that react with some minerals in rocks. Decaying remains of dead plants in soil may form organic acids and, when dissolved in water, may cause chemical weathering.

5.3 Erosion and Transportation

Agents of Erosion

Weathering

• Weathering
• Mass Wasting
• Erosion and Transportation
• Deposition and Depositional Landforms

Erosion is the process of transporting weathered sediments by agents of erosion to different places.

Glacier

• The physical breakdown and/ or chemical alteration of rocks at or near Earth’s surface.
• It is a degradation process and does not involve movement of materials.
• It has two types: mechanical and chemical weathering.

Wind

Wind caries dust, sand, and volcanic ash from one place to another. In dry areas, strong winds wears away soft rocks, and also polishes rocks and cliffs until they are smooth. Wind can also erode materials until nothing is left.

Transportation

Materials are transported in four distinct ways--- as solution, as suspension, by traction, or through saltation.

• Solution- materials are described in water and carried along by water.
• Suspension- the suspended particles are carried by medium (air, water or ice)
• Traction- particles move by rolling, sliding, and shuffling along eroded surface.
• Saltation- particles move from the surface to the medium in quick repeated cycles.

There are factors that affect the transportation of particles: particle weight, size, shape, surface configuration, medium type, resistance of particles to cohesions, and other environmental factors.

THANK YOU

Discussed by: Group 2

Maniacup, Melanie Angelica

Adona, Bryan

Morta, Camille

Ramos, Kristel Joy Marie

Punzalan, Harris

5.4 Deposition and Depositional Landforms

Deposition is the aggradation or accumulation of weathered sediments to create different landforms.

Water and Landforms

Whenever stream velocity decreases, it deposits the sediments it carries. The material deposits of stream is called alluvium.

Deltas are formed when river loses energy as it flows in to an area of slow-moving water, such as a lake or the sea.

Alluvial fans are formed when a stream reaches a flat area (called piedmont) or gently sloping plain.

Deltas are formed when river loses energy as it flows in to an area of slow-moving water, such as a lake or the sea.

Alluvial fans are formed when a stream reaches a flat area (called piedmont) or gently sloping plain.

Glaciers and Landforms

All unsorted deposits of rock formed directly by the ice are called glacial till.

Moraines are layers or ridges of till. A long pile of rocky material at the edge of a glacier is called lateral moraine while at the middle of the glacier is called medial moraine.

Esker is a winding ridge of sand and gravel deposited under a glacier by water melting from the ice.

Drumlins are streamlined asymmetrical hills composed of till. They may occur in clusters as drumlin fields.

Kames are steep-sided hills. Like eskers, they are composed of sand ang gravel.