Weathering, Erosion and Mass movement

Weathering is when external factors such as physical, biological and chemical factors are acted on rocks. It causes a breakdown on the structure of the rock and change in its shape all while staying in its original place.

Erosion is when broken down rocks (sediments) because of weathering, are moved from one place to another also because of external factors.

Mass movement is just an erosion but in a larger scale. It moves because of gravitational force. The gravity's force to even out all surface areas.

Weathering

  • The slow changes that results in crumbling, breaking up and destruction in any kind of rocks.

  • Other than the weather, action from biological, physical and chemical factors also implies.

Importance of weathering

  • Rock cycle - production of sediments which is the raw materials for new rocks. Weathering on igneous causes it to break and become sediments that are need for accumulation of new rocks.

  • Formation of soil - soil is the accumulation of rock fragments and organic matter. The sediments of broken down rocks mixes up with organic matters accumulates the soil.

  • Movement of rock materials over the earth's surface - before weathering, rocks is confined to one location. Weathering prepares the rock for erosion.

Erosion

  • Process of physical removing weathered rocks.

  • Weathering has prepared the rocks for erosion to pick up and for some agent or transportation to move or carry away the fragments that have been produced from solid rocks.

  • It can be moved to lower elevation because of gravity and through some agent such as water, wind and glaciers.

  • This happens in a small scale.

Mass movement

  • Erosion that's because of gravity is called mass movement of mass wasting.

  • So slow it is imperceptible.

  • Creep, the slow downhill movement of the soil down a steep slope. Only detectable because of trees growing.

  • Mass movement is a small victory for gravity. Gravity's force wants to even out all of the surface by pulling higher level regions to lower level regions.

Three criteria in the classification of mass movement

  • Type of material moved - identified by looking at what started the movement. e.g. Debris and Bedrock, debris such as soil, rock fragments or mixtures of rock materials are more likely to cause a movements since it's loose and crumbly compared to bedrock which is a solid rock.

  • Rate of movement - it can be as rapid as rock falling from a hill or as slow as several millimetres per year. Controlled by the amount of water in the soil and steepness of the hill.

  • Type of movement - these identifies how the movement takes place as fall, slip or flow.

    • Rocks can fall in vertical or nearly vertical cliff from higher regions to lower regions because of gravity

    • Rocks can also slip on slopes like creep. A) slump - curved area. B) slide - slope.

    • Rocks can also go with the flow of the water

Geological Processes that happens within the Earth's crust

Tectonic Plate theory

It states that earth's crust is divided into segment of landmasses also called as plates. This plates diverge and converge with each other that causes the deformation in the earth's surface. This plate movements results in geological features such as mountains.

Divergent boundaries - Divergent movement occurs at mid-ocean ridges when two tectonic plates drift away from each other. Divergent movement is mainly caused by the generated heat from the earth's core that motivates a convection in the plastic layer of the earth. As the plates seperate, a split is made where magma ascends and solidifies that forms the new oceanic crust. This movement may cause an earthquake in the process.

Convergent boundaries - This movement occurs when two plates with similar density move towards each other. Since they have similar density no subduction are made and it results in the uplifting of the land, forming various geological features such as mountain and mountain ranges.

Transform boundaries - Unlike divergent and convergent boundaries, transform boundaries involve lateral movement. Transform boundaries occurs when two tectonic plate are sliding past each other horizontally. This movement causes friction between plates that builds up into stress that become's earthquake when released.

Principle of Uniformity

States that same geological processes in rocks that happens before still happens today.

Diastrophism - process of deformation of earth's surface

Volcanism - process of elevating of magma from the crust to surface

Earthquake - when stress are released from the interaction between plates.

The connection between the three - we can relate it to the subduction boundary where denser plate subduct to less dense plate. This movement causes earthquake as well as deformation in the earth's surface. Once the crust are in the mantle it is then destroyed and produces magma which climbs towards the surface through volcanoes and cracks.

Stress

Force that deforms the rock

Strain - change that resulted from the applied stress

Rocks respond to stress depends on:

  • Nature of the rock - some rocks are more resistant to deformation while others are more prone to it.

  • Temperature - can also affect their behaviour. Rocks on warmer temperatures are more deformable than rocks on cold temperatures.

  • Stress applied overtime - rocks that are applied with immediate stress are more brittle and break while rocks that have stress applied slowly will bend and deform.

Folding and faulting of the rocks

Fold - the bending of the rocks because of compressional force or stress.

Monosyncline - Simple bend on the surface where the new rocks are on top region while the older rocks on the bottom region

Antisyncline - The rock arches upward where old rocks are near the center of the fault

Syncline - Rocks bends downward and new rocks are at the center

Fault - breaking of rocks into two blocks along with the displacement of it.