🌍 Earth Movements: Faulting and Folding

📚 Introduction: Forces Leading to Faulting and Folding

Earth movements are caused by internal and external forces and can be either lateral or vertical. These movements are vital in shaping the earth's surface.

• 🌋 Internal Forces: These forces operate within the earth’s surface and lead to earthquakes, volcanicity, folding, and faulting. They are also referred to as endogenic forces.
• 🌊 External Forces: These act on the earth's surface causing denudation, glaciations, river action, and wave action. These forces are also called exogenic forces.
• 🌎 Earth movements, also known as tectonic movements, play a role in creating relief features on the earth's surface.

🌀 Classification of Earth Movements

🐢 Slow Movements

• ⏳ Gradual changes to the earth’s surface that take hundreds or thousands of years.
• 🏔️ Can result in uplift, submergence, or subsidence of the earth's crust.
• ↕️ These movements act either vertically or horizontally.

⚡ Sudden Movements

• 💥 Abrupt changes to the earth's surface such as volcanic eruptions, landslides, and earthquakes.

↕️ Vertical and Horizontal Movements

🔼 Vertical Movements

• ⬆️ Up-and-down movements causing the earth's crust to fault.
• 🗺️ These movements are called epeirogenic movements and are slow and widespread.
• 🏞️ Vertical movements can result in the formation of continents, plateaus, oceans, block mountains, basins, and escarpments.

➡️ Horizontal Movements

• ↔️ Horizontal forces acting on the earth's crust result in the folding of rocks.
• ⛰️ These movements, known as orogenesis, produce landforms like fold mountains, rift valleys, and block mountains.

🔧 Forces of Tension and Compression

⚖️ Difference Between Compression and Tension Forces

💪 Compression Force: Exerts pressure from both sides, pushing towards the center, causing rock layers to crack or develop faults.

🎯 Tension Force: Exerts pressure in opposite directions, pulling rocks apart, also resulting in faults.

🌟 Forces of Tension

• 📏 Tensional forces lengthen the earth’s crust, creating faults. Landforms such as rift valleys, block mountains, and fault scarps result from tension.

🏋️ Forces of Compression

• 🔧 Compression forces shorten the earth's crust, leading to the bending of rock layers. Fold mountains are the result of compression forces.

⛰️ Folding

Folding is the bending of crustal rocks due to compression forces over a long period. This process forms complex folds like fold mountains or simple folds such as anticlines and synclines.

🔄 Types of Folds:

• 📐 Monocline Fold: Rock strata are pushed by compression forces against a hard plane.
• 🔺 Anticline Fold: Rock layers bend upward, forming an arch-like structure.
• 🔻 Syncline Fold: Rock layers bend downward, forming valleys.
• ⚖️ Simple Fold: Symmetrical fold with both limbs inclined at the same angle.
• 📉 Asymmetrical Fold: One limb is steeper than the other, formed by continued compression.
• 🔄 Overfold: Formed when one limb of an asymmetrical fold is pushed over the other.
• 🌐 Recumbent Fold: Extreme compression forces cause one limb to be pushed to a greater distance.
• ⚙️ Overthrust Fold: Extreme compression results in a fracture, where the upper part of the fold slides over the lower part.

🌍 Faulting

Faulting occurs when the earth’s crust is torn or fractured due to tension and compression forces, resulting in the displacement of rock blocks.

📏 Types of Faults:

• 🌊 Normal Fault: Caused by tensional forces where the middle block sinks, forming a rift valley.
• 🗻 Reverse Fault: Caused by compression forces where one block is pushed up over the other.
• 💢 Tear Fault: Caused by lateral forces where rock blocks slide past each other.

🏞️ Features Formed by Faulting:

• 🗻 Block Mountain (Horst): Formed when land between two faults is uplifted by compression forces.
• 🏞️ Rift Valley (Graben): A long narrow depression between two highlands, formed by the sinking of rock strata between parallel faults.
• 🛤️ Escarpments (Fault Scarps): Steep slopes along a fault line, often found in rift valleys and horsts.

💡 Theories on the Formation of Rift Valleys

🔗 Tension Theory:

Rift valleys form when tension forces create faults and the central block sinks.

🔗 Compression Theory:

Rift valleys form when compression forces push side blocks over the center, forming a trough.

🏔️ Importance and Problems of Faulting

🌟 Importance:

• 🌧️ Creation of highlands with reliable rainfall.
• 💧 Formation of lakes, which provide water and mineral resources.
• 🎯 Tourism opportunities due to impressive scenery.

⚠️ Problems:

• 🚧 Difficulty in transportation.
• 🔥 Hot, arid conditions in rift valleys.
• 🌪️ Soil erosion and mass wasting.

🌨️ Influence of Fold Mountains on Human Activities

Fold mountains often receive heavy rain or snow, giving rise to important rivers, such as those originating in the Alps.

🛠️ Benefits and Challenges of Rift Valleys

✅ Benefits:

• 💧 Water supply from lakes.
• ⚡ Geothermal energy production.
• 🌾 Grazing pastures and tourist attractions.

Challenges:

• 🌍 Earthquakes, flooding, high temperatures, and unreliable rainfall.
• 🚧 Poor transport and communication networks.
• 🌋 Soil erosion and volcanic activity affecting human settlement.

Problems Associated with Faulting

• 🚫 The development of transport facilities is hindered.
• 🔥 Rift valleys are very hot and experience little or no rainfall since they lie in the rain shadow.
• 🌾 Faulted areas experience severe soil erosion and mass wasting, which result in the destruction of soil surfaces, crops, and sometimes people’s property.

Influence of Fold Mountains on Human Activities

🌨️ Fold mountains often receive heavy rain or snowfalls, which give rise to important rivers, such as those originating in the Alps mountains in Europe.

Benefits of Rift Valleys

• 💧 Lakes in the Rift valleys provide water for domestic and industrial purposes, such as for irrigation in agriculture.
• ⛅ Modification of climate due to the existence of mountains.
• ⚡ Production of geothermal electricity from underground sources.
• 🐑 Rain shadow areas with low rainfall provide pasture for grazing.
• 🧂 Salt-water lakes are used for mining resources like soda ash.
• 🏞️ Tourist attractions with beautiful scenery provided by lakes, mountains, and escarpments.
• 🐘 Wildlife conservation areas.

Challenges/Problems Faced by People Living in the Rift Valley

• 🌋 Earthquakes (tremors).
• 🌊 Flooding.
• 🔥 High temperatures and little rainfall, leading to drought in the rain shadow areas.
• 🚧 Poor means of transport and communication.
• 🥀 Poor soils.
• 🧂 Salty lakes due to high evaporation rates.
• 💧 Shortage of water and unreliable rainfall.
• 🌾 Soil erosion and mass wasting.
• 🌋 Volcanic eruptions, which can destroy property and lives.

🌍 Physical Parts of the Earth

The earth is composed of several concentric layers. 🌎

The outer layer, called the earth’s crust or lithosphere, has two parts:

• 🔝 Upper part: Consists of granitic rocks, forming the continent. Its mineral constituents are silica and alumina. It is referred to as Sial and has a density of 2.7.
• 🌊 Lower part: Composed of basaltic rocks, forming the ocean floors. This layer consists of silica, iron, and magnesium (called Sima) with a density of 3.0.

The mantle (also called the mesosphere) lies below the earth’s crust, is 2900 km thick, and consists of dense rocks rich in olivine. 🪨

The core (barysphere) has a radius of about 3476 km and is composed of iron and nickel, known as NIFE. It has extremely high temperatures (~1927°C) and high pressure. 🔥

Part of the earth’s crust is submerged beneath oceans and seas, forming the hydrosphere. 🌊

🪨 Types of Rocks

The earth consists of various rocks differing in texture, structure, color, and permeability. These are classified into three major types:

• 🌋 Igneous Rocks: Formed from the cooling and solidification of molten magma beneath the earth's crust. They are crystalline and do not occur in layers or strata.
• 🗻 Plutonic Rocks: Formed within the earth’s crust.
• 🌋 Volcanic Rocks: Formed from molten lava that solidifies on the earth's surface.
• 📜 Sedimentary Rocks: Formed from accumulated sediments over a long period and occur in layers or strata. They may contain fossils and are classified into:
  • 🏖️ Mechanically Formed: Derived from the accumulation of materials like sandstones.
  • 🦴 Organically Formed: Formed from remains of living organisms, e.g., limestone.
  • ⚗️ Chemically Formed: Precipitated chemically from solutions.
• 🔥 Metamorphic Rocks: Created by the transformation of igneous or sedimentary rocks through intense heat and pressure.

📝 EXERCISE QUESTIONS

• ❓ State the two mineral constituents of SIAL.
• ❓ What are rocks formed by the cooling of molten rock called?
• ❓ Mention two characteristics of sedimentary rocks.

⛰️ Types of Mountains

• 🏔️ Fold Mountains: Formed by compressive forces that create wrinkles or folds in the earth’s crust (e.g., Himalayas, Rockies).
• 🏞️ Block Mountains: Formed when the earth’s crust cracks due to faulting, creating raised or sunken blocks (e.g., Rift Valley).
• 🌋 Volcanic Mountains: Created by volcanic activity when lava cools and solidifies around a vent.
• 🌄 Residual Mountains: Formed by denudation where resistant areas of land remain after the surrounding land has been worn down.

🌍 Types of Plateaus

• 🗺️ Tectonic Plateaus: Formed by tectonic movements uplifting extensive areas.
• 🌋 Volcanic Plateaus: Formed by the solidification of lava flows.
• 🌄 Dissected Plateaus: Formed through erosion processes over time.

🏞️ Types of Plains

• 🟫 Structural Plains: Found in areas where horizontally bedded rocks remain undisturbed by earth’s crustal movements.
• 🏞️ Depositional Plains: Formed by the deposition of materials brought by rivers or winds.
• 🌪️ Erosional Plains: Created by agents of erosion, such as rivers, ice, and wind.

🌋 VOLCANISM AND VULCANICITY

• 🔥 Vulcanicity: The process by which magma is intruded into or extruded from the earth’s crust.
• 🌋 Volcanicity: Refers specifically to how magma is extruded onto the earth’s surface.

🌋 Causes of Volcanicity:

• ⬆️ Increased magma pressure
• 🌀 Fissures and cracks allowing magma to escape
• 🔥 Increased magma temperature
• 🔄 Wider volcanic vents

🛠️ INTRUSIVE LAND FORMS

• 📏 Sill: A horizontal intrusion of magma along sedimentary layers.
• 📐 Dyke: A vertical intrusion of magma.
• 🏔️ Laccolith: A large, dome-shaped intrusion.
• 🪑 Lopolith: A saucer-shaped intrusion.
• 🔍 Phacolith: A lens-shaped mass.
• 🌄 Batholith: A massive intrusion forming resistant upland regions.

🌋 ORIGIN OF VOLCANOES

Volcanism is often linked to tectonic movements and zones of weakness in the earth’s crust. Magma rises due to gases and pressure, forming various types of volcanoes. 🌎

🔥 TYPES OF VOLCANIC LAVA

• 🌋 Acid Lava: Highly viscous, light-colored, and slow-moving.
• 🔥 Basic Lava: Hot, fluid, dark-colored, and fast-moving.

🌋 EXTRUSIVE LAND FORMS

Formed by the nature of lava and volcanic materials reaching the surface. Types of volcanic cones include:

• 🏞️ Lava Plateaus: Formed from basic lava.
• 🌋 Composite Cones: Built up by multiple eruptions.

🌋 EFFECTS OF VOLCANOES

Positive Effects:

• 🌱 Creation of fertile soils
• 💎 Formation of valuable minerals
• ⚡ Geothermal energy generation
• 🏞️ Tourist attractions (e.g., geysers and volcanic mountains)

💧 GEYSERS AND HOT SPRINGS

• 🌊 Geysers: Eruptions of superheated water and steam.
• 💦 Hot Springs: Heated water rising to the surface without an explosion.

🌍 EARTHQUAKES

Definition:
An earthquake is a sudden movement or vibration of the earth's crust. It can range from a faint tremor to a wild motion and is essentially the result of the ground surface's motion.

Causes of Earthquakes:

• 🌐 Movement of tectonic plates:
  • 🔀 Pull away from each other.
  • ⬆️⬇️ Push against each other.
  • ↔️ Slide sideways relative to each other.
• 🌋 Volcanic eruptions: Violent volcanic eruptions can place solid rock under stress, causing vibrations in the earth’s crust.

Nature of Earthquakes:

Earthquakes vary in intensity, from very severe to mild, and sometimes barely noticeable.

• 🎯 Focus: The point within the earth's crust where the earthquake originates. Also known as the hypocenter or seismic focus.
• 📍 Epicenter: The point on the earth's surface directly above the focus, where shock waves first hit the surface.

Types of Seismic Waves:

• 🔴 Primary Waves (P-Waves):
  • 🔄 Caused by compression.
  • 🌍 Travel through both solid rock and the Earth's liquid core.
  • ↔️ Move crustal rock back and forth in the wave direction.
• 🟢 Secondary Waves (S-Waves):
  • 🌍 Travel through surface rocks.
  • ↗️ Move at right angles to the wave direction.
  • 🐢 Slower than P-waves.
• 💨 Love Waves (L-Waves): Travel along surface rocks and cause rocks to move side-to-side in a horizontal plane.
• 🌊 Rayleigh Waves (R-Waves): Surface waves that cause particles to move in a vertical circular motion, like water in the sea.

Measurement of Earthquakes:

• 📊 Seismograph: The instrument used to record earthquake vibrations and measure intensity.
• 📏 Magnitude: Total energy released during an earthquake, measured on the Richter scale.
• 🌍 Intensity: The effect of the earthquake at the epicenter.

Effects of Earthquakes:

• 💔 Loss of life (human and wildlife).
• 🏚️ Destruction of infrastructure (roads, buildings, communication, and electric lines).
• 🔥 Breakout of fires from ruptured gas and water pipes.
• 🌍 Pollution of water, land, and air.
• 🦠 Spread of epidemics (e.g., cholera).
• 🏠 Displacement of people.
• 🌄 Landslides, rockfalls, and avalanches due to weakened natural slopes.
• 🌊 Tsunamis and soil liquefaction.
• ⬆️⬇️ Raising and lowering of parts of the seafloor.
• 🌧️ Flooding from river course damming.

Factors Contributing to the Intensity of Earthquakes:

• ⏳ Duration of shaking: Longer shaking causes more damage.
• 👥 Population density: More people are at risk in densely populated areas.
• 🌍 Distance from the epicenter: Shaking decreases with distance from the epicenter.
• 🏗️ Building quality: Poorly constructed buildings collapse more easily.
• 🪨 Local conditions: Soil and rock properties can affect wave characteristics and the intensity of shaking.

Measures to Reduce Adverse Effects of Earthquakes:

• 📚 Public education: Teach the public about earthquake preparedness.
• 🤝 Sensitization programs: Train teachers, architects, engineers, and community leaders.
• 🏢 Engineered buildings: Use designs that withstand seismic activity.
• 👨‍👩‍👧‍👦 Community preparedness: Engage the community in earthquake drills and response plans.
• 📜 Planning: Implement zoning laws and regulations that consider earthquake risks.

Distribution of Earthquakes:

Most earthquakes occur around the Pacific Ring of Fire, associated with tectonic plate activity.

• 🌍 Common earthquake regions:
  • 🌊 Mid-ocean ridges.
  • 🏝️ Volcanic islands and ocean deeps.
  • 🗻 Areas of crustal compression.

📝 REVISION QUESTIONS

1. 🔍 Mention any five causes of volcanic activity and volcanic eruption.
2. ⚡ Discuss factors contributing to the intensity of an earthquake.
3. 📡 The instrument used to record vibrations produced by earthquakes is called ___.
4. 💡 Discuss measures to reduce adverse effects of earthquakes.
5. 🏙️ Show how earthquakes can affect human life.
6. 🌋 ___ are fountains of super-heated hot steam that may spout up to the height of 45 meters from the earth’s crust.