Natural Phenomenon
Natural Phenomenon
🌍 Earthquakes
🔬 Causes of Earthquakes
- Tectonic Activity: Most earthquakes are caused by the sudden release of energy due to the movement of tectonic plates.
- Volcanic Activity: Earthquakes can occur due to magma movement beneath the Earth’s surface.
- Human Activity: Induced earthquakes can result from activities like mining, reservoir-induced seismicity, and hydraulic fracturing.
- Faulting: Earthquakes occur when stress builds up along faults and is suddenly released.
📊 Types of Earthquakes
| Type | Description | Example |
|---|---|---|
| Tectonic Earthquakes | Caused by movement of tectonic plates | San Francisco 1906 |
| Volcanic Earthquakes | Result from magma movement | Mount St. Helens 1980 |
| Collapse Earthquakes | Due to cave collapses or landslides | Not commonly recorded |
| Induced Earthquakes | Caused by human activities | Oklahoma (2016) |
📏 Measurement of Earthquakes
- Richter Scale: Measures the magnitude of an earthquake based on the amplitude of seismic waves.
- Moment Magnitude Scale (Mw): More accurate for large earthquakes, measures the total energy released.
- Mercalli Scale: Qualitative scale based on observed effects.
- Seismographs: Instruments used to record seismic waves.
📌 Important Facts for Exams
- Great Earthquake of 1906 (San Francisco): Magnitude 7.8 on the Richter scale.
- Earthquake in Japan (2011): Magnitude 9.0, caused by the Pacific Plate and Eurasian Plate.
- Earthquake in Nepal (2015): Magnitude 7.8, killed over 9,000 people.
- Earthquake in India (2001): Gujarat earthquake, magnitude 7.7, killed over 20,000 people.
🌋 Volcanoes
🧱 Types of Volcanoes
| Type | Description | Example |
|---|---|---|
| Shield Volcanoes | Broad, gently sloping shape | Mauna Loa (Hawaii) |
| Stratovolcanoes (Composite Volcanoes) | Steep, conical shape with explosive eruptions | Mount Fuji (Japan), Mount Vesuvius (Italy) |
| Cinder Cone Volcanoes | Small, steep-sided cones made of volcanic ash and cinders | Parícutin (Mexico) |
| Lava Dome Volcanoes | Formed by viscous lava extrusion | Mount St. Helens (USA) |
| Caldera Volcanoes | Large depressions formed by collapse | Yellowstone Caldera (USA) |
🌍 Distribution of Volcanoes
- Ring of Fire: A major area of volcanic and seismic activity around the Pacific Ocean.
- Mid-Atlantic Ridge: Active volcanic zone in the Atlantic Ocean.
- Continental Volcanoes: Found in areas like the East African Rift Valley.
- Hotspots: Volcanic activity not related to plate boundaries, e.g., Hawaii, Iceland.
🧪 Effects of Volcanoes
- Positive Effects:
- Fertile soil due to volcanic ash.
- Geothermal energy sources.
- Tourism and economic benefits.
- Negative Effects:
- Lava flows, pyroclastic flows, and ashfall.
- Volcanic gases (e.g., sulfur dioxide) can affect climate.
- Ashfall can damage infrastructure and agriculture.
📌 Important Facts for Exams
- Mount Vesuvius (Italy): Erupted in 79 AD, destroyed Pompeii and Herculaneum.
- Mount Fuji (Japan): Active stratovolcano, last eruption in 1707.
- Mount St. Helens (USA): Erupted in 1980, one of the most destructive eruptions of the 20th century.
- Mount Pinatubo (Philippines): Erupted in 1991, one of the largest eruptions of the 20th century.
- Volcanic Winter: Eruption of large volcanoes can lead to global cooling due to atmospheric ash and sulfur dioxide.
🌍 Plate Tectonics
🧠 Theory Overview
- Plate Tectonics Theory: Explains the movement of the Earth’s lithosphere, divided into tectonic plates.
- Key Concepts:
- Lithosphere: The rigid outer layer of the Earth.
- Asthenosphere: The semi-fluid layer beneath the lithosphere.
- Convection Currents: Heat from the Earth’s core drives the movement of tectonic plates.
- Plate Boundaries: Divergent, convergent, and transform boundaries.
📌 Types of Plate Boundaries
| Boundary Type | Description | Example |
|---|---|---|
| Divergent Boundaries | Plates move apart, creating new crust | Mid-Atlantic Ridge |
| Convergent Boundaries | Plates move towards each other, leading to subduction or collision | Himalayas (India-Eurasia), Andes (South America) |
| Transform Boundaries | Plates slide past each other | San Andreas Fault (USA) |
📌 Important Facts for Exams
- Continental Drift Theory (Alfred Wegener): Proposed in 1912, suggested continents were once joined.
- Seafloor Spreading (Harry Hess): Proposed in 1960, explained the creation of new oceanic crust.
- Plate Tectonics Theory (1960s): Unified the concept of continental drift and seafloor spreading.
- Mid-Atlantic Ridge: A divergent boundary where new oceanic crust is formed.
- Himalayas Formation: Result of the collision between the Indian and Eurasian plates (started ~55 million years ago).
- San Andreas Fault: A transform boundary in California, responsible for frequent earthquakes.
📌 Key Terms
- Tectonic Plates: Large sections of the Earth’s lithosphere.
- Subduction Zone: Area where one plate is forced under another.
- Volcanic Arcs: Form along subduction zones.
- Isostasy: The balance between the Earth’s crust and the mantle.
- Hotspots: Areas of volcanic activity not related to plate boundaries.
📌 Exam-Focused Summary
- Plate Tectonics is the unifying theory of geology.
- Divergent boundaries create new crust.
- Convergent boundaries lead to mountain building and subduction.
- Transform boundaries cause earthquakes.
- Key examples: Himalayas, Mid-Atlantic Ridge, San Andreas Fault.
BETA
