The term tsunami, derived from Japanese, translates to “harbour wave.” It refers to a succession of extremely long-wavelength oceanic waves produced by substantial disturbances, most often linked to earthquakes occurring beneath or in proximity to the seafloor. Additionally, subaqueous volcanic eruptions and submarine landslides can act as catalysts for tsunami formation. These phenomena present a significant threat to both human life and infrastructure, particularly for populations residing in coastal regions. While some tsunamis have reached towering heights exceeding 100 feet, even those ranging between 10 and 20 feet possess the potential to be profoundly destructive, frequently resulting in notable casualties, widespread injuries, and essential property damage.
Causes
Tsunamis are most commonly triggered by earthquakes; however, not every seismic event results in tsunami formation. For a tsunami to be generated, the earthquake must occur either beneath or in close proximity to the ocean, possess considerable magnitude, and induce significant displacement of the seafloor. Although tsunami events can potentially impact all oceanic zones worldwide, the Pacific Ocean experiences a notably higher frequency of large-scale, destructive tsunamis. This elevated occurrence is due to the prevalence of major seismic activity along the tectonic boundaries that encircle the Pacific basin. In addition to earthquakes, other less frequent yet notable causes of tsunamis include submarine landslides, underwater volcanic eruptions, and, on rare occasions, the impact of a massive meteorite in the ocean.
Propagation
In the open ocean, a tsunami typically exhibits a wave height of only a few feet at the surface; however, as it approaches shallow coastal areas, its height increases rapidly. The wave energy of a tsunami extends vertically from the ocean surface to the seabed, even in profound depths. As the wave advances toward the shoreline, this energy becomes compressed into a shorter wavelength, resulting in intensely destructive and life-threatening waves. The magnitude and impact of these waves are heavily influenced by offshore and coastal features, such as reefs, bays, river mouths, submarine topography, and the beach slope—all of which modify the tsunami’s behavior as it approaches land. Upon reaching the shore and moving inland, the water level may rise significantly. In extreme events, this rise can exceed 50 feet for tsunamis originating from distant sources and surpass 100 feet when generated near the earthquake’s epicenter.
When traveling through ocean depths exceeding 20,000 feet, tsunami waves—though barely noticeable—can attain velocities comparable to commercial jet aircraft, approximately 600 miles per hour. This extraordinary speed allows them to cross the entire Pacific Ocean in less than 24 hours. Due to this rapid movement, early awareness of a tsunami’s generation is crucial. Scientists are able to forecast arrival times, as tsunami speed is directly related to the square root of the water depth. As tsunamis move into shallower coastal zones, their velocities decrease, while their wave heights increase dramatically, intensifying the potential for severe destruction.
Consequences
The consequences of a tsunami range widely, from the loss of livelihood for coastal communities—particularly fishermen—to extensive and often undocumented damage to coral reefs, as well as marine and coastal ecosystems. The recovery of coral reef systems may require several years to restore ecological balance, while mangrove forests and coastal tree plantations often suffer severe destruction or irreversible damage.
The influx of seawater deep into inland areas leads to salination, a critical impact that reduces soil fertility, thereby impeding vegetative growth. This salinity not only undermines agricultural productivity but also heightens susceptibility to erosion, exacerbates the effects of climate change, and contributes to long-term food insecurity. From a human-centric perspective, sectors such as fisheries, housing, and infrastructure experience the most significant and immediate impacts, often requiring substantial time and resources for recovery.
Early Warning and Mitigation
Several major tsunami warning centers operate globally to monitor seismic and oceanographic activity, aiming to provide timely alerts and facilitate effective mitigation strategies.
Pacific Tsunami Warning Center (PTWC):
Functioning as the operational hub of the Pacific Tsunami Warning System (TWS), PTWC is supported by 26 participating international Member States. It monitors data from seismological and tidal stations across the Pacific Basin to assess earthquakes that may generate tsunamis. Upon detection of a tsunami-genic event, PTWC disseminates crucial warning information to national authorities within the Pacific region. Located near Honolulu, Hawaii, it plays an essential role in safeguarding Pacific Rim nations from potential tsunami hazards.
Alaska Tsunami Warning Center (ATWC):
Based in Palmer, Alaska, the ATWC operates as the regional warning authority for Alaska, British Columbia, Washington, Oregon, and California. It delivers timely notifications and risk assessments, serving as a primary node in the tsunami alert network for the North American west coast.
Indian Tsunami Early Warning System (ITEWS):
The Indian Tsunami Early Warning System is responsible for issuing tsunami advisories to both the Indian mainland and its island territories. Recognized as one of the Regional Tsunami Advisory Service Providers (RTSPs) for the Indian Ocean Region, ITEWS collaborates with Australia and Indonesia to offer regional tsunami guidance to the surrounding Indian Ocean Rim countries. Its strategic function contributes significantly to enhancing preparedness and response capabilities across vulnerable zones.
To verify whether an earthquake has indeed resulted in a tsunami, it is essential to record changes in sea level with high precision, especially in close proximity to the fault zone. This determination relies on data obtained from two primary types of sea level measuring instruments: coastal tide gauges and open-ocean buoys.
Tide gauges are typically installed at the land-sea boundary, often in areas that are partially sheltered from the intense wave activity generated by storm systems. Although these gauges may provide minimal advance notice at the immediate site where the tsunami is first detected, they serve a crucial function in informing coastal communities—where the waves have not yet arrived—of the presence of a tsunami, along with estimations of its velocity and potential intensity. This early indication can prove vital in issuing alerts and initiating protective actions before the tsunami reaches populated coastal areas.
Open-ocean tsunami buoy systems, which are outfitted with bottom pressure sensors, have emerged as a reliable and advanced technology capable of delivering early warnings to coastal regions likely to be impacted first by a tsunami. These systems can detect tsunami waves before they arrive at nearby tide gauges, offering critical lead time for issuing alerts. In many cases, open-ocean buoys provide a more accurate prediction of the tsunami’s intensity than tide gauges located farther from the seismic event.
In addition to technological solutions, the use of natural barriers plays a crucial role in mitigating tsunami impacts. Coral reefs function as natural breakwaters, forming a physical obstruction that diminishes wave energy before it strikes the coastline. Similarly, mangrove forests act as natural shock absorbers, absorbing destructive wave force and serving as a buffer against coastal erosion. These ecosystems offer significant protection and enhance the resilience of vulnerable coastal areas against the devastating effects of tsunamis.