Tectonics and Geology: Landscape Evolution

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Table of Contents

Plate tectonics
Geological Agents
Landscape Responses
Hydrological Impacts
Magnitude and Frequency
Works Cited

Plate tectonics

The rigid outer layer of the plate’s surface is called lithosphere (plate tectonics) while the inner layer is called asthenosphere (plate interiors). Their differences are explained in their mechanical, chemical subdivision and physical properties as illustrated in the table below;

Plate Margins	Plate Interiors
On physical properties plate margins forms the rigid outer layer	Inner layer composed of melted rocks and is composed of denser fluids that allow rocks to float
Lithosphere composed of two tectonic plates; thicker continental and thin oceanic. Upper part called crust while the lower part mantle
Mechanical properties; lithosphere losses heat by conduction	Asthenosphere transfers heat by convection
Higher strength and lower density	Lower strength and higher density
Cooler and rigid	hotter and flows more easily
Exist as separate and distinct
Overlain by two crustal materials; oceanic crust (sima-from silicon and magnesium)
Lithosphere
Oceanic	Continental
A depth of approximately 100km (63miles). Its thickness characterised by age since when its conductivity cools it becomes thicker	A depth of approximately 35km
The thickness varies from 6km to 100km at subduction zones	200 km thick and varies between mountain ranges, basins and the stable cratonic interiors of the continents
Formed at mid ridged and spreads outwards
Oceanic crust lies below sea level for example the Pacific Rime	continental crust projects above sea level for example the West Coast of Australia
Formed at sea-floor spreading centres,	Continental crust formed as a result of arc volcanism and accretion of terranes through tectonic processes (pieces of oceanic crust).

The resultant landscapes commonly associated with geological events includes activities such as oceanic trenches, earthquakes, mountain building and volcanic activities that often result to topographical features that subsequently results to deformation of landscapes and possibly loss of human lives. Based upon abnormalities that often associate tectonic movements active volcanic eruptions are said to occur along plate boundaries.

Geological Agents

Humans are now referred as the most geological agent on the planet’s surface by trying to modify different parts of the Earth’s landscape. The processes that outstrip natural and anthropogenic processes include activities such as agriculture, construction and mining. Other activities such as building reservoirs for holding floods said to lessened erosion have been highly criticised for increasing erosion since the bulk of erosions are evidenced to occur above dams.

Deforestation activities are also considered to encourage floods and promote erosion by interfering with natural circulation of air and water. Rock uplift and erosional denudation of natural orogenic belts transport sediments during physical breakdowns exposing rocks and minerals to drainage basins. Man’s activities interfere with natural agents by causing abrasion and removing weathered and un-weathered rocks by encouraging formation of quarries that cut through channels causing artificial glaciers.

Fluvial sediment fluxes resulting from combined influence from both human and geological activities cause changes in drainage basins and destruction of sea coasts as a result of suspended loads deposited on major river systems and oceans. Land reclamation activities such as agricultural activities have adversely strained the inanimate nature on the environment.

Wilkinson & McElroy (141) studies evidenced that regions that have undergone intense human modification through predominant construction and mining activities have adversely been affected. Glacial processes as a result of human impacts such as underground mines, disposal of industrial waste, and strip mining have also contributed to erosion. Underground mining such as extracting base metals, limestones, gypsum cause roof tops and surfaces to collapse increasing acids and toxic waters to the environment by mine flooding.

As noted by Wilkinson & McElroy (142), decrease in rock volume as a result of strip mines and Open-Pit Mines resulting from large-scale quarrying and open pit mining for stones, asphalt, other non fuel resources, stone, gravel and sand destruct the clastic and carbonate sediments by causing carbonate accumulation by sub-aerial erosion and subduction of deeper oceanic oozes which may subsequently result to oceanic trenches.

Coal fields developed as a result of large earth moving equipments resulted to surface mining-ponds and toxic water resources. Construction activities aimed at urbanising the environment such as building of highways, parking lots, drive ways and quarry benches destruct the natural sedimentary rocks which may eventually collapse as a result of destruction of natural soil topography by mixing materials that may not be fully compatible with the natural soil leading to land subsiding.

In addition to topographical slope as a major erosional agent, many investigations have linked Industrial waste disposals from both liquid and solid waste disposals such as surface burials in soils or rock units, and subsurface injections which may find their way into natural waterways as major influences of environmental degradation. Moreover, a broader scale of consideration, waste disposal management should be given top priority to ensure toxic materials remain isolated from the ground water aquifers and biosphere. Conclusively, permeable sedimentary rocks such us dolomite should be considered in the construction of waste containment (Wilkinson & McElroy 154).

Landscape Responses

Theories built on older geological concepts argue that tectonic movements result to significant landscape responses such as mountain building, earthquakes and ocean trenches that can have adverse effects to human lives. This theory can be evidenced by the recent earthquakes and landslides reported in the media recently. The recent earthquakes experienced in the East African, particularly in Ugandan region for instance have been reported to be as a result of Earth’s shifting tectonic plates causing significant land responses.

Previous, qualitative studies on landslides have found that human induced activities such as intense deforestation, economic and geomorphological events are contributing factors to landslides in Uganda, however there is little research and documentation to support analysis. Research also reports that high annual rainfall, high weathering rates and slope materials with low sheer strength are considered the preparatory casual factors for landslides (mass movement).

The frequency and magnitude are important to a geologist as they help detect the motion of tectonic plates which may be helpful in predicting future tectonic plate movement that causes earthquakes. Gravity and frequency relationship is also important in identifying tectonic deformations and landsides as they help study activities that induce slope instability. For example when large rotation slides involving volcanic rocks move tectonically in active regions, geologists give warning of possible landslides and earthquakes preparing human beings for such calamities. Recent landslides in Uganda around Kapchorwa and Mbale (the mountainous areas) could be associated with soil-mantled steep hill slopes triggered by intense rainstorms.

Research also adds that mass movements associated with intense rainstorms reported to have occurred periodically in the region since the early 20^th century are evidenced as casual factors of landslides. In addition, increased population pressure and tampering of human impact should be reduced by avoiding terracing of slopes and construction of artificial structures concentrating water to vulnerable zones. In support of this analysis, neotectonic studies have shown strong influence of plate boundary processes on the recent earthquake in China.

Based on simplified map of major tectonic units, neotectonic data mainly based on Quaternary faults slips evidenced that earthquakes in China that occurred within Indo-Eurasian plate boundary was triggered by weak altered volcanic rocks and heavy rains affecting the slope stability. Studies also stipulate that strong influence of plate boundary processes of the diffused crustal formation could be the major cause of earthquakes. Weak crustal form because of intense seisimicity and dense population could be among other causes of the recent earthquake in China (Wilkinson & McElroy 2007).

Hydrological Impacts

Hydrological impacts due to urbanisation have compromised water quality such as sedimentation, habitant changes, loss of fish and increased temperatures. Most hydrological impacts are caused by runoff volumes and velocities of trying to urbanise cities causing major strain to the water streams. Hydrologic impacts on water streams due to increased impervious include activities such as construction of dams, parking lots, rooftops and roads.

Increased Imperviousness leads to:	Resulting Impacts
	Flooding	Habitat loss (inadequate substrate, loss of riparian areas, e.t.c)	Erosion	Channel widening	Streambed alteration
Increased volume	*	*	*	*	*
Increased peak flow	*	*	*	*	*
Increased peak flow duration	*	*	*	*	*
Increased stream temperature		*
Decreased base flow		*
Changes in sediment loadings	*	*	*	*	*

Urbanisation and increased watershed has had intense hydrologic impacts on water streams by affecting their natural course compromising quality of water. These problems are also attributed by heavy reliance on engineered approaches and runoff management such a construction of pavement channels, storm water pipes and bank stabilization (Wilkinson & McElroy 144).

Magnitude and Frequency

Magnitude and frequency relationships are important to geosciences because they are used in studying catastrophic events. They evaluate the relative amounts of work done on the landscapes over the long-term by events of all magnitudes. Geologists also conclude that large parts of sediment transportation are performed by events of moderate magnitude that recur relatively frequently, rather than rare events of unusual magnitude.

In this regard, gravity is the bus that drives sediments of the sea, sediment transports in streams. The nature of the movement of sediments by water or air is dependent upon magnitude and frequency. On implications of geomorphic effectiveness on the formation of rivers and channels, erosion process is driven by gravitational force acting on water drives water down slope in a confined channel, where the water surface represents the balance between the energy gradient and friction resistance from channel beds and banks. Magnitude and gravity bring about shear and flow products of water depth.

Here, when water levels exceed bankfull stage, water flows out on the floodplain and increases water flow. The effectiveness of processes on the formation of river channels depends on their distribution in time and their magnitude. For example, the major portion of work performed by events of moderate magnitude which recur relatively frequently than by rare events of unusual magnitude. Magnitude/frequency analysis effectiveness has been demonstrated throughout geomorphology.

Effectiveness in terms of supply and transport of materials by geomorphic process, sediment transportation by rivers operate relatively frequently and are low threshold process. Channel modification by erosion and disposition are also as a result of magnitude frequency relationship since their relationship transport materials in/out of the catchment. In terms of channel distribution, higher peak discharge and flow durations above a given threshold level may cause channel alterations (Wilkinson & McElroy 2007, 144).

Works Cited

Schueler, Richard. The Stream Protection Approach: Guidance for Developing Effective Local Nonpoint Source Control Programs in the Great Lakes Region. Silver Spring, Maryland :U.S. Environmental Protection Agency, 1994.

Wilkinson, Bruce., & McElroy, Brandon. “The impacts of humans on continental erosion and sedimentation.” Geological Society of America Bulletin 119 (2007): 140-156.

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