Tsunami Formation and Causes

Overview

The lecture explains the formation, causes, and impacts of tsunamis, the role of tectonic plates, and methods for early warning and mitigation.

Tsunami waves travel fast in open ocean but have low amplitude and are hard to notice.
As tsunamis approach shallow water, their speed decreases and amplitude increases dramatically, causing devastation.
The increase in amplitude near shore is called wave shoaling, caused by reduced wavelength and constant wave energy.
Tsunami waves involve energy transfer, not horizontal water movement; particles oscillate in place.
Tsunami crests or troughs may reach shore first; a receding shoreline can indicate an incoming tsunami but is not always present.

The Earth's surface consists of seven major tectonic plates floating on the molten core due to convection.
Plates interact by diverging (rift valleys), converging (mountains, trenches, volcanoes), or sliding past each other.
Most earthquakes and tsunamis occur at tectonic plate boundaries.
Subduction zones, where denser oceanic plates sink under continental plates, store and suddenly release strain energy, triggering earthquakes and tsunamis.

The 2004 Indian Ocean tsunami was caused by a major subduction zone earthquake near Sumatra, measuring 9.1–9.3 on the Richter scale.
The tsunami killed over 340,000 people, with waves up to 30 meters high and speeds up to 800 km/h.

Underwater earthquakes are the leading cause of tsunamis.
Other causes include underwater volcanic eruptions, underwater or coastal landslides, and rare meteorite impacts.

Prior to 2004, the Indian Ocean had no tsunami warning system; now, buoys and seabed sensors detect water level changes and transmit warnings via satellite.
Early warnings can help evacuate coastal regions before tsunami arrival.
Japan built sea walls up to 15 meters high for tsunami protection, but exceptional waves have overtopped these defenses.
Early predictions of wave height may underestimate tsunami risk, as seen in the 2011 Japan tsunami.

Tsunami — A series of ocean waves caused by large displacements of water, usually from underwater earthquakes.
Tectonic Plates — Large sections of the Earth's crust that move over the molten mantle.
Subduction Zone — A region where one tectonic plate slides beneath another, often causing earthquakes and tsunamis.
Wave Shoaling — The increase in wave amplitude as it moves into shallower water.
Seawall — A structure built along the coast to reduce the impact of waves, including tsunamis.

Review the main causes and warning signs of tsunamis.
Study diagrams of tectonic plate boundaries and subduction zones.
Understand how early warning systems work and investigate local evacuation plans in tsunami-prone areas.