Tsunamis are powerful ocean waves triggered by underwater disturbances like earthquakes or landslides. They can travel at incredible speeds across vast distances, growing in height as they approach land. These destructive waves pose a significant threat to coastal areas worldwide.

Understanding tsunami formation and impacts is crucial for coastal communities. From early warning systems to land-use planning, various strategies can help mitigate the devastating effects of these natural disasters. This knowledge is vital for protecting lives and infrastructure in vulnerable coastal regions.

Causes of Tsunamis

Seismic Activity

• Submarine earthquakes occur when tectonic plates suddenly move vertically along a fault line beneath the ocean floor, displacing massive volumes of water and generating tsunami waves
• Thrust faults, where one plate is forced under another (subduction zones), are particularly prone to generating tsunamis as they cause significant vertical displacement of the seafloor
• The magnitude and depth of the earthquake determine the size and speed of the resulting tsunami waves, with shallow, high-magnitude earthquakes posing the greatest tsunami risk

Submarine Mass Movements

• Submarine landslides, triggered by earthquakes, volcanic activity, or slope instability, can displace large volumes of water and generate localized tsunamis
• Rockfalls and debris flows occurring above or below the water surface can also cause sudden water displacement and tsunami formation
• Volcanic island collapses, such as the potential failure of the Cumbre Vieja volcano on La Palma (Canary Islands), could generate massive tsunamis capable of traversing entire ocean basins

Tsunami Dynamics

Wave Propagation and Characteristics

• Tsunami waves in deep ocean have long wavelengths (up to hundreds of kilometers), low amplitudes (less than a meter), and high velocities (up to 800 km/h), making them difficult to detect in open waters
• As tsunami waves approach shallower coastal waters, their wavelength decreases, velocity slows, and amplitude increases dramatically, potentially reaching heights of tens of meters
• Tsunami wave trains can consist of multiple waves, with subsequent waves often being more destructive than the initial wave due to constructive interference and resonance effects

Coastal Interactions

• Run-up refers to the maximum vertical height a tsunami wave reaches above normal sea level as it moves onshore, and is influenced by factors such as coastal topography, bathymetry, and wave characteristics
• Inundation describes the horizontal distance inland that a tsunami wave penetrates, which depends on run-up height, coastal elevation, and land use (e.g., urban areas, forests)
• Drawback occurs when the trough of a tsunami wave reaches the shore, causing a temporary retreat of the waterline and exposing the seafloor, often luring curious onlookers into dangerous areas before the next wave arrives

Coastal Impact and Mitigation

Vulnerability Factors

• Low-lying coastal areas, such as beaches, estuaries, and river deltas, are particularly vulnerable to tsunami inundation due to their low elevation and flat topography
• Densely populated coastal cities and towns are at high risk of casualties and infrastructure damage during a tsunami event, as seen in the 2004 Indian Ocean tsunami (affected countries like Indonesia, Sri Lanka)
• Inadequate coastal defenses, such as seawalls and breakwaters, can exacerbate the impact of tsunamis on coastal communities and ecosystems

Mitigation Strategies

• Early warning systems, such as the Pacific Tsunami Warning Center (PTWC) and the Indian Ocean Tsunami Warning System (IOTWS), use seismic data, deep-ocean buoys, and coastal tide gauges to detect tsunamis and issue alerts to at-risk populations
• Tsunami hazard maps and evacuation plans help identify vulnerable areas and guide people to safe zones or evacuation routes, improving preparedness and response times
• Coastal land-use planning, such as preserving natural barriers (mangrove forests, coral reefs) and limiting development in high-risk areas, can reduce the exposure and vulnerability of coastal communities to tsunami impacts