Plate Tectonics & Earth Hazards

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Plate Tectonics: Global Distribution The distribution of active volcanoes, earthquake epicenters, and major mountain belts are closely linked to the Earth's plate boundaries. These features primarily occur along divergent, convergent, and transform plate boundaries. 1. Active Volcanoes Location and Distribution: Ring of Fire: A major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur. It's a horseshoe-shaped belt, approximately 40,000 km long, home to over 75% of the world's active and dormant volcanoes. Mid-Ocean Ridges: Occur along divergent plate boundaries where new oceanic crust is formed. Examples include the Mid-Atlantic Ridge. Subduction Zones: Common along convergent plate boundaries where one plate slides beneath another. Volcanic arcs (e.g., Andes Mountains, Japanese Islands) form above the subducting plate. Rift Valleys: Found at divergent plate boundaries on continents, like the East African Rift Valley. Hotspots: Isolated volcanic activity away from plate boundaries, caused by mantle plumes (e.g., Hawaii, Yellowstone). Types of Plate Boundaries: Convergent (Oceanic-Continental/Oceanic-Oceanic): Most common location for explosive volcanoes due to subduction. Divergent: Produce effusive (non-explosive) volcanism, often underwater. 2. Earthquake Epicenters Location and Distribution: Plate Boundaries: Over 90% of all earthquakes occur along plate boundaries. Ring of Fire: The same region that hosts most volcanoes also accounts for about 90% of the world's earthquakes. Oceanic Trenches: Deep earthquakes are characteristic of subduction zones where oceanic crust descends into the mantle. Mid-Ocean Ridges: Shallow, frequent earthquakes occur here as plates pull apart. Transform Faults: Characterized by shallow to intermediate depth earthquakes, often with significant magnitudes (e.g., San Andreas Fault). Continental Collision Zones: Produce broad zones of shallow to deep earthquakes (e.g., Himalayan region). Intraplate Earthquakes: Less common, but can occur within tectonic plates due to accumulated stress (e.g., New Madrid Seismic Zone). Depth of Earthquakes: Shallow Earthquakes ($ Occur at all plate boundaries, especially divergent and transform. Intermediate Earthquakes ($70-300 \text{ km}$): Primarily found in subduction zones. Deep Earthquakes ($>300 \text{ km}$): Exclusively found in subduction zones where cold, dense oceanic crust penetrates deep into the mantle. 3. Mountain Belts Location and Distribution: Convergent Plate Boundaries: The primary mechanism for mountain building. Continental-Continental Collision: When two continental plates collide, neither subducts significantly, leading to intense folding, faulting, and uplift of crustal material to form massive mountain ranges (e.g., Himalayas, Alps). Oceanic-Continental Convergence: Subduction of an oceanic plate beneath a continental plate creates volcanic mountain ranges along the continental margin (e.g., Andes Mountains, Cascade Range). Oceanic-Oceanic Convergence: Subduction leads to the formation of volcanic island arcs (e.g., Japanese Alps, Aleutian Islands). While not always "mountain belts" in the continental sense, they are elevated landforms due to volcanic activity. Rift Mountains: Formed along divergent plate boundaries where blocks of crust are uplifted as the land stretches and thins (e.g., Basin and Range Province in the US, East African Rift mountains). Erosion/Uplift: Older mountain ranges (e.g., Appalachians, Urals) are remnants of ancient plate collisions, now significantly eroded. Key Characteristics: Often characterized by folded and faulted sedimentary and igneous rocks. Associated with intense seismic and volcanic activity, especially at active convergent boundaries.