Introduction
Earthquakes and volcanism are primary endogenic geomorphic phenomena driven by the release of Earth's internal thermal energy and mantle convection. While earthquakes represent the sudden release of strain energy radiating seismic waves through the lithosphere, volcanism involves the ascent and eruption of molten rock (magma) onto the Earth's surface.
Causes of Earthquakes
Earthquakes occur primarily due to the sudden dislocation of rock along fractures or faults within the crust and upper mantle, explained fundamentally by Reid's Elastic Rebound Theory.
- Tectonic Dislocation: Accumulation of tectonic stress exceeds rock friction along plate boundaries, causing sudden failure.
- Convergent Margins: High-magnitude megathrust earthquakes generated along subduction zones (e.g., the Magnitude 7.4 Noto Peninsula earthquake in Japan, January 2024).
- Transform Margins: Lateral shearing where plates grind horizontally past each other without creation or destruction of crust (e.g., the San Andreas Fault system).
- Divergent Margins: Normal faulting along rift valleys and mid-oceanic ridges as crust is pulled apart.
- Volcanic Seismicity: Movement and ascent of magma generate harmonic tremors and fracture surrounding bedrock, serving as pre-eruptive precursors.
- Anthropogenic and Induced Seismicity: Human engineering interventions altering local crustal stress regimes, such as Reservoir-Induced Seismicity (e.g., the 1967 Koyna Dam earthquake), deep-well fluid injection, and deep-shaft mining operations.
- Intraplate and Isostatic Adjustments: Reactivation of ancient palaeo-faults within cratonic interiors and post-glacial crustal rebound.
Causes of Volcanic Activities
Volcanism requires generation of magma, driven by specific thermodynamic conditions that induce melting of the asthenosphere and lithosphere.
- Decompression Melting at Divergent Boundaries: Upwelling convective mantle beneath rift zones experiences a drop in lithostatic pressure without loss of heat, crossing the solidus and melting peridotite into basaltic magma (e.g., Mid-Atlantic Ridge and Iceland's Fagradalsfjall volcanic systems).
- Flux Melting (Hydration Melting) at Convergent Boundaries: Subducting oceanic lithosphere releases trapped hydrated minerals and water into the overlying mantle wedge. These volatiles lower the melting temperature of mantle rock, creating silica-rich, viscous, and explosive magma (e.g., Pacific Ring of Fire; Mount Lewotobi Laki-laki in Indonesia).
- Mantle Plumes and Intraplate Hotspots: Localised thermal anomalies rising from the core-mantle boundary (D″ layer) induce partial melting far from active plate margins, forming persistent volcanic tracks across moving plates (e.g., the Hawaiian-Emperor seamount chain and the active shield volcanism of Mauna Loa).
Conclusion
While endogenic forces driving seismicity and volcanism cannot be halted, comprehensive seismic micro-zonation, resilient construction engineering, real-time geochemical monitoring, and multi-hazard Early Warning Systems are indispensable for reducing vulnerability and safeguarding life.