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Chapter 14. Geology

Recommended Post : 【Earth Science】 Table of Contents


1. Up-lift Geographic Motion

2. Down-lift Geographic Motion

3. Plate Tectonics



1. Up-lift Geographic Motion

Type 1. Atmospheric Erosion

① Mechanical Destructive Action

② Chemical Decomposition

③ Weathering and Soil Formation

○ Development of Soil : The state of soil due to the actions of climate, reproduction, groundwater, etc.

○ Types of Soil Formation : Tundra Soil, Podzol, Gray Brown Forest Soil, Chernozems, Solontshak and Solonetz, Red Soil, Laterites, Prairie Soil, Tirs, Rendzina, Terra Rossa, Moor

○ Soil Profile : Initially categorized by Russian soil scientists using the A, B, C horizon system

○ Types of Soil : Original Soil, Transported Soil

Type 2. Erosion by Freshwater : Can be classified into surface water, subsurface water, groundwater, and lake water erosion

Type 2-1. Erosion by Surface Water

Type 2-2. Erosion by Subsurface Water

① Alluvial Fans and Alluvial Plains

② Streams

○ Outer Side of Streams : Active erosion due to higher kinetic energy

○ Inner Side of Streams : Slower flow with reduced transport capacity leading to deposition

○ Positive Feedback : Streams develop in the direction of greater curvature

③ Alluvial Plains

④ Floodplains

○ Cause : Intense deposition due to reduced flow velocity

○ Differences in Triangle Diagrams, Classifications, and Source Materials

⑤ Delta and Alluvial Fans

⑥ River Mouths

⑦ Cyclic Nature of Erosion

○ Young Terrain

○ Mature Terrain

○ Old Terrain

Type 2-3. Erosion by Groundwater

Type 2-4. Erosion by Lakes

Type 3. Erosion by Seawater

① Destructive Action of Seawater

② Constructional Action of Seawater

Type 4. Erosion by Glaciers (Glacial Erosion)

① Types of Glaciers

○ Local Glaciers : Valley Glaciers, Alpine Glaciers, also known as Alpine-Style Glaciers

○ Continental Glaciers (Antarctica) : Begin moving outward from a central point

○ Ice Sheet, Ice Cap : Cover a substantial land area with an ice thickness facing downwards

○ Piedmont Glaciers : Valley glaciers that merge and expand at the foot of mountains, like in Alaska

② Flow Velocity and Size of Glaciers

③ Glacial Landforms

○ Cirque

○ Hanging Valley

○ Glacial Lake

○ Fjord

○ Moraine

④ Transport and Depositional Action of Glaciers

Type 5. Erosion by Organisms

① Destructive Action

② Constructional Action



2. Down-lift Geographic Motion

⑴ Regulation Movement

① Evidence of Melting Movement : Melt Pits, Coastal Erosion, Parallel Discordances, Shell Holes on the Pillars of Serapis Temple

② Evidence of Subsidence Movement : Subsidence Coast

⑵ Orogenic Movement and Moisture-Curve Monolayer

① Moisture-Curve : Rock layers bending due to lateral pressure on strata

○ Anticline : Upward-convex moisture-curve

○ Syncline : Downward-concave moisture-curve

② Types of Moisture-Curves

○ Normal Folding

○ Inclinal Folding

○ Isoclinal Folding

○ Recumbent Folding

○ Fan-Shaped Folding

○ Dome-Shaped Folding

○ Centroclinal Folding

③ Fault

○ Hanging Wall : Upper portion relative to the fault plane

○ Footwall : Lower portion relative to the fault plane

○ Normal Fault : Hanging wall is below footwall, caused by tension

○ Reverse Fault : Hanging wall is above footwall, caused by compression

④ Fault Movement

○ Step Fault

○ Splintered Fault

○ Tilted Block

○ Overthrust Fault

⑶ Orogenic Periods and Arrangement of Mountain Ranges

① Arrangement of Mountain Ranges

○ Anticlinal Valleys

○ Chains

⑷ Volcanic Phenomena

① Principles of Volcanic Activity

② Gains and Losses from Volcanic Activity

⑸ Earthquakes

① Overview

○ Seismic Intensity : Measures earthquake damage

○ Magnitude : Measures energy released during an earthquake

② Causes of Earthquakes

○ Fault Origin Hypothesis

○ Igneous Origin Hypothesis

③ Earthquake Weather

④ Changes in Terrain due to Earthquakes

⑹ Stratigraphic Principles of Geology

① Principle of Uniform Processes

○ Proposed by James Hutton

○ Claims Earth’s history is longer than the 6,000 years suggested by the Bible

② Principle of Superposition

③ Principle of Biological Evolution

④ Principle of Inclusion

⑤ Principle of Disconformity

⑺ Interpretation of Strata

① Conformity and Disconformity

○ Conformity : Layer with continuous deposition

○ Disconformity : Layer with signs of halted deposition for a considerable period

○ Parallel Disconformity : Layers above and below appear parallel, like conformity

○ Angular Disconformity : Layers above and below meet at an angle due to uplift

○ Discordant Intrusion : Intrusion in disconformity plane, observed in angular disconformity

○ Unconformity : Layer eroded due to disconformity

② Dip and Strike : (Note) Original layers deposited horizontally but tilted due to tectonic movements

○ Strike : Intersection line between

strata and horizontal plane

○ Dip : Angle between strike and the bedding plane of a rock layer. 0° ≤ θ ≤ 90°

○ Symbols for Strike and Dip on Maps

○ Strike represented as ‘ㅜ’, dip as a short line

○ Example of Strike : N30°E

○ Example of Dip : 25°SE = 25°NW

○ Horizontal layers represented as ⊕

○ Clinometer

Figure 1. Clinometer

○ Strike : Represents the direction of true north.

○ Dip : Represents the direction of gravity.

○ Bubble in the spirit level : Indicates horizontality when located at the center. Should be centered when measuring strike.

○ Measurement of strike : Long side of the clinometer should be parallel to the strike line. The outer number indicated by the needle represents the strike.

○ Measurement of dip angle : Long side of the clinometer should be parallel to the bedding plane. The inner number indicated by the dip needle represents the dip angle.

○ Measurement of dip direction : Measure strike using the direction of the dip needle.

③ Interpretation

○ Horizontal intrusion : When lava intrudes parallel to the surface.

○ Dyke : When lava intrudes vertically to the surface.

○ Fault : A specific part of the ground rising. Occurs along with intrusion.

○ (Note) Extrusive features are not related to intrusion.

Submarine Basaltic Ridge : Observed in the deep ocean.

Submarine Volcanic Ridge : Observed in shallow seas.

Figure. 2. Submarine Volcanic Ridge[Note:1]

○ Definition : Layered structure formed by irregular sedimentation due to flowing water, wind, etc.

○ Formed in shallower depths or basins.

○ Indicates wind or water direction during deposition of layers.

○ Well represented in volcanic rocks.

○ Not observable in bedding planes.

Erosion : Traces of flowing water. Observed in shallow seas.

Figure. 3. Erosion[Note:2]

○ Observable in bedding planes.

Desiccation : Marks of ground splitting due to drying. Observed in dry climates.

⑧ Cross-section and Three-dimensional Model of Geological Structures

Figure. 4. Cross-section and Three-dimensional Model of Geological Structures[Note:3]



3. Plate Tectonics

⑴ Evidence of Continental Drift Proposed by Wegener

① Continuity of geological structures observed across the Atlantic Ocean.

② Identical plant fossils found on various continents.

③ Traces of Ice Age glaciers in tropical regions.

④ Matching coastlines of South America and Africa.

⑤ (Note) Later, inconsistencies in the path of movement were discovered in paleomagnetic studies and became accepted as the theory.

⑥ (Note) The peninsula landmasses during the Ice Age were located between the southern peninsula and the equator.

⑵ Driving Forces of Plate Motion

Factor 1: Mantle convection

Factor 2: Slab pull

○ Plates are denser as they are subducted.

○ Result: Plates are dragged upwards due to tension.

Factor 3: Slab suction

○ Slabs detach and rapidly descend during subduction.

○ Result: Intensification of mantle convection, subduction of plates.

Factor 4: Ridge push

○ Ridges push plates away with gravitational slopes.

⑶ Major Plates and Boundaries

Figure. 5. Major Plates and Boundaries[Note:4]

① Continental Plate

② Oceanic Plate

⑷ Divergent Boundary (E) : Oceanic Plate - Oceanic Plate

Characteristic 1: Trenchless earthquakes due to the absence of subducted plates.

Characteristic 2: Tholeiitic magma. Active volcanic activity.

○ Tholeiitic magma is generated deeper and contains more iron.

○ Mostly tholeiitic magma in divergent boundaries.

Characteristic 3: Formation of oceanic lithosphere at divergent boundaries.

○ Thickness of the plate increases as moving away from rift.

○ Heat flow decreases as moving away from rift, representing the rise of mantle convection.

○ Depth increases as moving away from rift.

○ Age of oceanic lithosphere increases as moving away from rift.

○ Sediments on the ocean floor increase as moving away from rift.

④ Terrain : Mid-ocean Ridge (e.g., Mid-Atlantic Ridge, East Pacific Rise)

⑸ Divergent Boundary (A) : Continental Plate - Continental Plate

Characteristic 1: Tholeiitic magma.

○ Tholeiitic magma is generated deeper and contains more iron.

○ Mostly tholeiitic magma in divergent boundaries.

Characteristic 2: Formation of rift valleys.

② Terrain : Rift valley (e.g., East African Rift)

③ Divergent boundaries are mainly observed in oceanic plates.

○ Heat flow from mantle convection concentrates mainly in oceanic plates.

○ Continental plates act as insulators and do not focus heat flow.

○ Heat flow in continental plates is transferred by radioactive elements.

⑹ Convergent Boundary : Oceanic Plate - Oceanic Plate

Characteristic 1: Shallow and deep earthquakes.

○ Shallow earthquakes occur together with deep earthquakes.

○ Due to subduction of denser oceanic plates, deep earthquakes occur.

Characteristic 2: Tholeiitic or andesitic magma.

○ Tholeiitic magma when both subduct and generate magma at greater depths, containing more iron.

○ Andesitic magma when one oceanic plate is pushed upwards.

Characteristic 3: Volcanic arcs.

Volcanic Arcs: Chains of islands formed by volcanic activity about 100-400 km away from subduction zones towards the continent.

○ Volcanic arcs are the most representative structures at convergent boundaries between oceanic plates.

○ Andesitic magma is observed in volcanic arcs or subduction zones, while tholeiitic magma is observed beneath volcanic arcs.

○ Volcanic arcs are also called volcanic chains or island arcs.

Characteristic 4: Increase in density at the convergent boundary.

○ Denser oceanic lithosphere reaches the mantle faster and sinks beneath it.

○ Hydrous minerals with abundant hydroxyl groups (OH groups) lower melting points and increase volatility.

⑺ Convergent Boundary : Oceanic Plate - Continental Plate

Characteristic 1: Shallow and deep earthquakes.

○ Shallow earthquakes occur together with deep earthquakes.

Characteristic 2: Andesitic magma.

○ Andesitic magma is generated at shallower depths and contains less iron.

○ Produced due to the subduction of oceanic plates pushing the continental plate upwards.

Characteristic 3: Almost always involves subduction of oceanic plates : Due to higher density of oceanic plates.

Characteristic 4: Volcanic Arcs : Volcanic arcs develop at the convergent boundary between oceanic and continental plates.

Figure. 6. Formation of Volcanic Arcs at Oceanic-Continental Plate Boundary[Note:5]

⑤ Terrain : Andes Mountains, Nazca Plate - South American Plate

○ The continental landmasses are well developed on the eastern side of South America where no trench develops.

⑻ Convergent Boundary : Continental Plate - Continental Plate (B)

Characteristic 1: Trenchless earthquakes due to the absence of subducted plates.

Characteristic 2: No magma formation.

○ Reason: No subduction of continental plates.

○ No pathway for magma to escape.

○ Granitic magma intrusion can occur.

Characteristic 3: Thrust faulting with the involvement of the principal stress direction.

○ (Note) Transformation fault : Mainly generated at trenches. Formed due to differences in speed.

④ Terrain : San Andreas Fault, Transform Fault

⑼ Transform Boundary (D)

Characteristic 1: Trenchless earthquakes due to the absence of subducted plates.

Characteristic 2: No volcanic activity : No chance for magma to emerge.

Characteristic 3: Shear stress involved in the movement of the principal stress.

○ (Note) Conversion fault : Primarily generated at ridges. Formed due to differences in speed.

④ Terrain : San Andreas Fault, Conversion Fault



Input : 2019.04.07 12:11

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