VULCANISM AND EARTHQUAKES

1. Volcanic Intrusive Landforms

Volcanic intrusive landforms are geological features sculpted beneath the Earth's surface, created by the intrusion of magma. These formations play a vital role in shaping the Earth's crust and contribute to the diverse landscapes we observe. Among the prominent intrusive landforms are laccoliths, lopoliths, phacoliths, batholiths, sills, and dykes.

• Laccolith: Laccoliths emerge as magma intrudes between rock layers, causing the overlying rocks to arch upward. This process results in a distinctive lens-shaped structure, with a flat base and a domed top. The Henry Mountains in Utah showcase notable laccolithic formations.
• Lopolith: Lopoliths form when magma is injected into the Earth's crust, inducing a sagging effect on the overlying rock layers. These landforms exhibit a basin-shaped structure, characterized by a flat top and a concave base. The Duluth Complex in Minnesota is an exemplar of lopolithic features.
• Phacolith: Phacoliths take shape as curved or arched intrusions of magma, causing the surrounding rock layers to bend. These structures often develop in zones of geological weakness, such as folds or faults. Phacoliths contribute to the deformation of rock layers in the Earth's crust.
• Batholith: Batholiths are massive intrusive landforms, representing irregularly shaped bodies of solidified magma beneath the Earth's surface.  These formations cover extensive areas and are often associated with mountain-building processes. The Sierra Nevada Batholith in California is a prominent illustration.
• Sills: Sills are tabular intrusions of magma that run parallel to existing rock layers. Magma is injected horizontally between sedimentary layers, creating sheet-like structures. Sills contribute to the horizontal expansion of intrusive features.
• Dykes: Dykes are vertical or near-vertical intrusions of magma that cut across existing rock layers.  Magma rises along fractures, creating wall-like structures that traverse different geological formations. The Giant's Causeway in Northern Ireland showcases remarkable basaltic dykes.

2. Origins and Geological Processes

• The term "volcano" finds its roots in Vulcan, the Roman god of the underworld and fire.
• Intrusive landforms often occur at zones of geological vulnerability, such as folds or faults.
• Magma's upward movement is fueled by temperature increases, averaging about 1°F for every 65 feet of depth.

Intricacies of Magma: Magma carries gases like CO2, sulfur, nitrogen, and chlorine, which are released through vents or openings. The Earth's surface is altered by the presence of these gases, contributing to various geological phenomena.

3. Volcanic Origin and Characteristics

• Temperature Dynamics: Magma's ascent involves a temperature increase of approximately 1°F for every 65 feet of depth. This gradual temperature rise contributes to the molten nature of magma.
• Magma Composition: Magma is laden with gases, including 𝐶𝑂2 (carbon dioxide), sulfur, nitrogen, and chlorine. These gases are expelled through volcanic vents or openings during eruptions.

4. Types of Lava

Acidic Lava: Light-colored, highly viscous (thick and sticky), slow-flowing. Results in steep-sided volcanoes. Produces pyroclasts (fragmented rock and volcanic ash), bombs, and may form a spine or plug. Mount Pelée in Martinique, where the eruption led to the destruction of St. Pierre, and Puy de Dôme in France, featuring a volcanic plug.

Basic Lava: Hottest, highly fluid (runny), dark-coloured due to high content of iron (Fe) and magnesium (Mg). Flows quietly and spreads over large areas, forming thin sheets. Creates shield or dome-shaped volcanoes. Shield volcanoes, such as those in Hawaii, exemplify basic lava characteristics.

5. Exploring the Lifecycle of Volcanoes

Volcanoes are dynamic geological features, and their classification into active, dormant, or extinct categories provides insights into their current state of activity. Let's delve into the characteristics of each type:

• Active Volcano: An active volcano is currently erupting, has erupted recently, or is expected to erupt shortly. Kilauea in Hawaii is a quintessential active volcano. It has been consistently erupting since 1983, with lava flows and intermittent explosive eruptions.
• Dormant Volcano: A dormant volcano is not currently erupting but has the potential to erupt in the future. It has experienced recent activity, but an eruption is not imminent. Mauna Kea in Hawaii is considered dormant. While it hasn't erupted in about 4,600 years, it is still considered capable of erupting in the future.
• Extinct Volcano: An extinct volcano has not erupted in the last several thousand years and is not expected to erupt again. Kohala in Hawaii is classified as extinct. It last erupted over 60,000 years ago, and there is currently no geological evidence suggesting future activity.

6. Diverse Forms of Volcanic Landscapes

Volcanic extrusive landforms result from the eruption of magma onto the Earth's surface, shaping the landscape in various ways. 

• Lava Plains and Basalt Plateaux: Formed by highly fluid lava, resulting in expansive plains and plateaus. Examples: Snake Basin, USA; Deccan Plateau, India; Iceland.
• Lava Domes or Shield Volcanoes: Constructed by the accumulation of lava, creating a broad, shield-like structure. May have calderas with active vents, such as Mauna Loa and Kilauea in Hawaii. Halemaumau is a caldera with an active vent, forming a lava pit.
• Ash & Cinder Cones: Formed by less fluid lava, resulting in steep-sloped cones. Often found in groups and feature large craters. Examples: Mt. Nuovo in Naples, Italy; Mt. Paricutin in Mexico.
• Lava Tongues & Lava-Dammed Lakes: Lava flows confined in valleys can create tongues or dams, altering the local topography.
• Lava Bridges: These occur when lava flows solidify over a depression or gap, forming a bridge-like structure.
• Lava Tunnels: Formed when the outer layer of a lava flow solidifies while the molten interior continues to flow, creating tunnel-like structures.
• Volcanic Dust: Composed of fine particles released during volcanic eruptions.
• Dust and Ash - Black Snow: Volcanic ash, when settled, can resemble black snow, covering the landscape.
• Pyroclast - Coarse Fragments: Includes cinders/lapilli, scoria, pumice, and volcanic bombs, which are ejected during explosive eruptions.

7. Composite Cones

Composite cones, also known as stratovolcanoes or stratocones, are among the most impressive volcanic formations on Earth. 

Characteristics of Composite Cones

• Composite cones are renowned for their significant height, making them some of the tallest volcanic structures.
• They are formed through the alternating eruption of lava flows and pyroclastic material (ash, rocks, and volcanic gases).
• The name "composite" arises from the layered structure, representing different types of volcanic deposits.

Stratocones - Main Conduit and Subsidiary Dykes and Pipes

• Main Conduit: Composite cones have a central vent or main conduit through which magma ascends from the Earth's mantle.
• Subsidiary Dykes and Pipes: Additional channels, known as subsidiary dykes and pipes, facilitate the movement of magma from deeper reservoirs.

Notable Examples of Composite Cones

• Mt. Etna (Sicily, Italy): One of the most active volcanoes in the world, Mt. Etna stands as the highest and most prominent composite cone in Europe.
• Mt. Stromboli (Lighthouse of the Mediterranean): This iconic volcano is characterized by nearly continuous minor eruptions, earning it the nickname "Lighthouse of the Mediterranean."
• Mt. Vesuvius: Famous for its eruption in 79 AD, which buried the Roman cities of Pompeii and Herculaneum.
• Mt. Fuji: A symbol of Japan, Mt. Fuji is an iconic stratovolcano with a near-perfect cone shape.
• Mt. Popocatepetl: Located in Mexico, it is the second-highest peak in the country and is part of the Trans-Mexican Volcanic Belt.
• Mt. Chimborazo: A stratovolcano in Ecuador, its summit is the farthest point on Earth's surface from the Earth's centre due to the equatorial bulge.

9. Distribution of Volcanoes 

• Circum-Pacific Ring of Fire: This horseshoe-shaped zone, containing nearly 75% of the world's active volcanoes, circles the Pacific Ocean like a fiery necklace. Think of it as a hot spot where tectonic plates collide, creating a recipe for volcanic activity. Active volcanoes abound in this region, with countries like the Philippines (100), the Andes (40), Japan (35), and Indonesia (70) boasting impressive numbers.
• Pacific Coast: A Hotbed of Activity: The Pacific side of the ring reigns supreme in terms of active volcanoes. Think of fiery chains like the Aleutian Islands, Java and Sumatra in Indonesia, Kamchatka in Russia, the Solomon Islands, and New Hebrides.
• Atlantic Coast: A Smoldering Echo: While less active than the Pacific side, the Atlantic coast still boasts its share of volcanic heat. Madeira, Ascension, Helena, Cape Verde, and the Canary Islands are just a few examples.
• Iceland and Azores: Volcanic Outposts: These islands, nestled in the middle of the Atlantic, are volcanic gems, offering stunning landscapes and geothermal wonders.
• Mediterranean: Echoes of Ancient Fury: The Mediterranean region, associated with the Alpine fold mountains, boasts iconic volcanoes like Vesuvius, Etna, Stromboli, and Volcano, each with a history of fiery eruptions.
• Himalayan Enigma: No Fire in the Ice: Despite the towering peaks of the Himalayas, no active volcanoes grace their slopes. This highlights the complex interplay of tectonic forces that dictate volcanic distribution.
• Africa: Rift Valley Rumble: The East African Rift Valley, a zone of continental rifting, hosts active volcanoes like Cameroon, while extinct giants like Kilimanjaro and Kenya stand as majestic reminders of past fiery episodes.
• Geysers and Hot Springs: Nature's Boiling Beauty: While not volcanoes themselves, geysers and hot springs are often associated with volcanic regions. Think of the majestic eruptions of Old Faithful in Yellowstone National Park, the bubbling geysers of Iceland and Rotorua in New Zealand, or the serene hot springs of Hawaii and Japan.

10. Earthquakes

Earthquakes, the powerful expressions of tectonic forces beneath the Earth's surface, leave an indelible mark on our planet.

• Frequency and Magnitude: Earth experiences around 50,000 tremors annually. Tremors range from minor vibrations to major events occurring along faults, causing significant ground movement.
• Tsunamis and Secondary Effects: Earthquakes beneath the ocean floor can trigger tsunamis, causing massive oceanic waves. Fires, building collapses, surface fissures, and infrastructure damage are common aftermaths.
• Monitoring and Measurement: Sophisticated instruments like seismographs measure seismic waves, aiding in earthquake monitoring.  Earthquakes are measured on the Richter scale, indicating their magnitude and impact.

Historical Significance

• Great Lisbon Earthquake (1755): Striking the Atlantic west, it generated tidal waves, claiming 60,000 lives.
• Tokyo-Yokohama (1923): Caused extensive damage in Japan.
• San Francisco (1906): Infamous for its destruction.
• Agadir, Morocco (1960): Resulted in a tragic loss of 10,000 lives.
• Kakh, E. Iran (1968): Significant seismic activity in Eastern Iran.

Global Distribution

• Coincidence with Volcanoes: Earthquake-prone regions often coincide with volcanic activity.
• Circum-Pacific Belt (Ring of Fire): About 70% of earthquakes occur in the Circum-Pacific belt, known for intense seismic activity.
• Mediterranean-Himalayan Belt: This belt, covering 20% of global earthquakes, extends from the Mediterranean region to the Himalayas.