Volcanism:
Volcanism refers to the geological processes through which molten rock (magma) from the Earth’s interior is ejected onto the surface. It involves the formation of volcanoes, volcanic islands, and other landforms. The process occurs due to the movement of tectonic plates, which creates fissures and allows magma to escape.
Mechanism: Magma forms beneath the crust due to high temperature and pressure. When the overlying rock weakens, magma rises through fissures, creating volcanic activity. Upon reaching the surface, it becomes lava.
Example: The Hawaiian Islands were formed through continuous volcanic eruptions.
Types of Volcanoes
- Active Volcanoes: These volcanoes frequently erupt or show continuous activity.
Example: Mount Etna (Italy), Kilauea (Hawaii). - Dormant Volcanoes: These volcanoes have not erupted for a long time but may erupt again.
Example: Mount Vesuvius (Italy). - Extinct Volcanoes: These volcanoes have not erupted in recorded history and are unlikely to erupt again.
Example: Mount Kilimanjaro (Tanzania).
Volcanic Landforms
- Lava Plateaus: Formed by extensive lava flows covering large areas.
Example: Deccan Plateau in India. - Shield Volcanoes: Broad, dome-shaped volcanoes with gentle slopes formed by fluid lava flows.
Example: Mauna Loa (Hawaii). - Composite Volcanoes (Stratovolcanoes): Steep, conical volcanoes built from alternating layers of lava and ash.
Example: Mount Fuji (Japan). - Calderas: Large, basin-shaped depressions formed after the collapse of a volcanic cone.
Example: Crater Lake (USA).
Volcanic Materials
- Lava: Molten rock expelled by a volcano during an eruption. It solidifies upon cooling.
- Ash and Dust: Fine particles ejected during explosive eruptions, which can travel over large distances.
- Pyroclastic Flows: Fast-moving currents of hot gas, ash, and volcanic debris.
- Volcanic Bombs: Large molten rock fragments ejected during eruptions.
Example: The 1883 Krakatoa eruption released massive pyroclastic flows.
Extrusive Landforms
Extrusive landforms are created when magma reaches the Earth’s surface and solidifies as lava. These landforms vary based on the viscosity, volume, and type of lava.
- Lava Plateaus: Formed by repeated lava flows over large areas, resulting in flat, elevated surfaces.
Example: Deccan Plateau (India). - Volcanic Cones: Conical hills or mountains formed by successive eruptions of lava and ash.
Example: Mount Mayon (Philippines). - Cinder Cones: Steep, conical hills made of volcanic debris, with short-lived eruptions.
Example: Parícutin (Mexico). - Basalt Plains: Extensive flatlands formed by the outpouring of low-viscosity basaltic lava.
Example: Columbia Plateau (USA). - Calderas: Large, circular depressions formed when a volcano collapses after an eruption.
Example: Yellowstone Caldera (USA).
6. Some Notable Volcanic Eruptions
- Krakatoa (Indonesia, 1883): One of the deadliest eruptions, producing massive tsunamis and altering global weather patterns.
- Mount Vesuvius (Italy, 79 AD): Destroyed the Roman cities of Pompeii and Herculaneum, burying them under volcanic ash.
- Mount St. Helens (USA, 1980): A major eruption that caused massive landslides, ashfall, and pyroclastic flows.
- Eyjafjallajökull (Iceland, 2010): Disrupted European air travel due to ash clouds, highlighting the far-reaching impacts of volcanic eruptions.
- Mount Tambora (Indonesia, 1815): Triggered the “Year Without a Summer” due to massive ash emissions, causing global cooling.
7. Distribution of Volcanoes Around the World
Volcanoes are unevenly distributed, mainly along tectonic plate boundaries and hotspots.
- Circum-Pacific Belt (Ring of Fire): The most active volcanic zone, encircling the Pacific Ocean. It contains around 75% of the world’s active volcanoes.
Example: Mount Fuji (Japan), Mount St. Helens (USA). - Mid-Atlantic Ridge: An underwater volcanic range, formed by divergent tectonic plates.
Example: Iceland’s volcanoes. - East African Rift Valley: An area of tectonic divergence with several volcanoes.
Example: Mount Kilimanjaro and Mount Nyiragongo. - Mediterranean Belt (Alpide Belt): A seismically active zone running from Southern Europe to Asia.
Example: Mount Etna (Italy). - Hotspots: Volcanism occurring away from plate boundaries due to mantle plumes.
Example: Hawaiian Islands (USA).
8. Geysers
Geysers are hot springs that intermittently eject columns of water and steam due to underground geothermal activity. They occur when groundwater comes into contact with hot volcanic rocks.
Mechanism:
- Water seeps into the ground and reaches areas of high temperature.
- The water heats up, turning into steam, creating pressure.
- When the pressure exceeds the rock’s capacity, it erupts as a geyser.
Example: Old Faithful in Yellowstone National Park (USA) erupts at regular intervals.
9.Hot Springs
Hot springs are natural outflows of heated groundwater, often enriched with dissolved minerals. They are found in geothermal regions where magma heats underground water.
Mechanism:
- Water percolates through permeable rocks and reaches heated areas near magma chambers.
- The heated water rises to the surface, creating a hot spring.
- The temperature and mineral content vary based on local geology.
Example: Manikaran Hot Springs (India) in Himachal Pradesh are famous for their religious and therapeutic significance.
10. Earthquakes
An earthquake is a sudden shaking or vibration of the Earth’s surface caused by the release of energy in the lithosphere. It occurs due to tectonic movements, volcanic activity, or human-induced factors.
Causes:
- Tectonic Movements: Earthquakes occur at plate boundaries due to collision, subduction, or slipping.
- Volcanic Activity: Magma movement can create seismic waves.
- Human Activities: Mining, reservoir-induced seismicity, and nuclear tests can trigger earthquakes.
Example: The 2015 Nepal earthquake was caused by the collision of the Indian and Eurasian plates.
11. Seismic Waves
- Primary Waves (P-Waves): Fastest seismic waves that travel through solids, liquids, and gases.
- Secondary Waves (S-Waves): Slower waves that only travel through solids.
- Surface Waves: Slowest waves that cause the most damage, moving along the Earth’s surface.
Example: The 2004 Indian Ocean earthquake generated massive surface waves, causing a devastating tsunami.
12. Earthquake Zones and Distribution
- Circum-Pacific Belt (Ring of Fire): The most seismically active zone, encircling the Pacific Ocean.
- Alpide Belt: Extends from the Mediterranean region to the Himalayas.
- Mid-Atlantic Ridge: An underwater mountain range prone to earthquakes.
Example: The 2011 Tōhoku earthquake in Japan occurred in the Ring of Fire.
13. Earthquake Measurement
- Richter Scale: Measures the magnitude of an earthquake based on the energy released.
- Modified Mercalli Scale: Measures the intensity based on observed damage and human perception.
- Moment Magnitude Scale (Mw): Used for large earthquakes, measuring the total energy released.
Example: The 2001 Gujarat earthquake had a magnitude of 7.7 on the Richter scale.
14. Earthquake Hazards and Mitigation
- Hazards: Ground shaking, surface rupture, landslides, tsunamis, and infrastructure damage.
- Mitigation: Seismic-resistant construction, earthquake drills, and early warning systems.
- Disaster Management: Evacuation plans, relief measures, and international cooperation are essential.
Example: Japan’s advanced early warning system reduces earthquake casualties.
15. Some Major Earthquakes
- 2004 Indian Ocean Earthquake and Tsunami (Magnitude 9.1)
- Location: Off the west coast of Sumatra, Indonesia.
- Impact: Triggered a massive tsunami, affecting 14 countries and causing over 230,000 deaths.
- Cause: Subduction of the Indian plate beneath the Burma plate.
- 2011 Tōhoku Earthquake (Magnitude 9.0)
- Location: Off the northeastern coast of Honshu, Japan.
- Impact: Generated a devastating tsunami, damaging the Fukushima Daiichi nuclear plant.
- Cause: Pacific Plate subducting beneath the Okhotsk Plate.
- 2015 Nepal Earthquake (Magnitude 7.8)
- Location: Gorkha District, Nepal.
- Impact: Over 9,000 deaths and widespread destruction in Kathmandu Valley.
- Cause: Collision of the Indian and Eurasian plates.
- 1906 San Francisco Earthquake (Magnitude 7.9)
- Location: San Andreas Fault, California, USA.
- Impact: Widespread fires and structural damage, with over 3,000 deaths.
- Cause: Lateral movement along the San Andreas Fault.
- 2001 Gujarat Earthquake (Magnitude 7.7)
- Location: Bhuj, Gujarat, India.
- Impact: Over 20,000 deaths and extensive damage to infrastructure.
- Cause: Intraplate seismic activity along the Kutch fault.
16. Distribution of Earthquakes Around the World
Earthquakes are primarily concentrated along tectonic plate boundaries, where the Earth’s crust experiences the greatest stress.
- Circum-Pacific Belt (Ring of Fire):
- The most seismically active zone, encircling the Pacific Ocean.
- Accounts for nearly 90% of the world’s earthquakes.
- Major Earthquakes: 2011 Tōhoku earthquake (Japan), 1960 Valdivia earthquake (Chile).
- Alpide Belt:
- Extends from Southern Europe through the Himalayas to Southeast Asia.
- Formed due to the collision of the Eurasian, African, and Indian plates.
- Major Earthquakes: 2005 Kashmir earthquake, 2015 Nepal earthquake.
- Mid-Atlantic Ridge:
- An underwater seismic zone where the Eurasian and North American plates diverge.
- Earthquakes here are mostly of moderate intensity.
- Major Earthquakes: 2022 earthquake near the Azores Islands.
- East African Rift Valley:
- A zone of tectonic divergence in Eastern Africa.
- Earthquakes here are associated with rift valley formation.
- Major Earthquakes: 2006 Mozambique earthquake.
- Intraplate Earthquakes:
- Occur within tectonic plates rather than at boundaries.
- Often less frequent but can be destructive.
- Major Earthquakes: 2001 Gujarat earthquake (India), 1811–1812 New Madrid earthquakes (USA).
