Understanding Tsunamis: What Causes Them and Why They’re So Deadly

News Desk

Islamabad: A massive 8.7 magnitude earthquake struck off Russia’s Far East coast on Wednesday, sending tsunami alerts reverberating across the Pacific and reigniting global concerns about one of nature’s most catastrophic and unpredictable phenomena.

Although rare, tsunamis have a devastating history of reducing entire coastal communities to rubble within minutes with waves racing as fast as jetliners and powerful enough to fling ships onto rooftops.

The latest seismic jolt has renewed focus on the science behind tsunamis, their deadly potential, and the lessons still being learned from past tragedies around the world including Pakistan.

What is a Tsunami?

A tsunami — from the Japanese words tsu (harbour) and nami (wave) is a massive sea wave triggered mainly by undersea earthquakes. These quakes often occur when tectonic plates shift suddenly, displacing colossal volumes of water either by thrusting the ocean floor upward or causing it to drop.

Unlike regular waves driven by wind, tsunami waves are generated by seismic forces and can silently traverse entire oceans. In deep water, they may rise only a few centimetres but travel at speeds up to 800 km/h — akin to a commercial airliner. On reaching shallower coastal zones, these waves slow down and rise dramatically in height, transforming into destructive walls of water.

Other Triggers

While most tsunamis originate from seismic activity beneath the ocean, they can also be caused by volcanic eruptions, underwater landslides, glacier collapses, or even meteorite impacts.

One of the earliest recorded tsunamis struck in 365 AD off Crete’s coast, with Roman historian Ammianus Marcellinus documenting the sea’s abrupt retreat and its monstrous return — flinging ships into buildings in Alexandria.

In 1883, the eruption of Indonesia’s Krakatoa volcano unleashed a tsunami that killed over 30,000 people. The eruption’s thunder was reportedly heard more than 4,500 kilometres away.

The Science Behind the Devastation

Several factors influence how destructive a tsunami can be:

Magnitude of the triggering event – Stronger quakes generate more powerful tsunamis.

Seafloor topography – Shallow coastal shelves can increase wave height.

Proximity to populated areas – Densely populated coastlines near seismic zones are especially at risk.

Natural barriers – Mangroves, coral reefs, and forests can absorb some of the energy, reducing the impact inland.

The Pacific “Ring of Fire,” a belt of intense seismic and volcanic activity circling the Pacific Ocean, remains the most tsunami-prone region globally. Countries like Japan, Indonesia, Chile, and the US (especially Alaska) have robust early warning systems in place due to their exposure.

Telltale Signs and Multiple Waves

Tsunamis often strike with little to no warning, but some natural cues may serve as life-saving alerts. A sudden and unusual withdrawal of water from the shoreline — often mistaken for an extreme low tide — is a notorious sign of an impending tsunami.

Survivors of past disasters report that tsunamis frequently consist of multiple waves. While the first may cause substantial damage, it’s often followed by larger, more devastating surges minutes or even hours later.

The 2004 Indian Ocean Catastrophe

On December 26, 2004, a colossal 9.1 magnitude earthquake off the coast of Sumatra triggered the deadliest tsunami in modern history. The event released energy equal to nearly 23,000 Hiroshima bombs, killing around 220,000 people across 11 countries, including Indonesia, Sri Lanka, India, and Somalia.

Most victims received no warning. The Indian Ocean lacked a tsunami detection or alert system at the time, leading to a global push to install seismic and satellite-based technologies for future preparedness.

Pakistan’s Tsunami Risk

Pakistan’s 990-kilometre coastline, particularly the Makran Subduction Zone along Balochistan, remains vulnerable to tsunamis. In 1945, an 8.1 magnitude earthquake in the region triggered waves that struck Karachi and Gwadar, killing approximately 4,000 people.

While the Pakistan Meteorological Department (PMD) has since collaborated with regional bodies to bolster tsunami monitoring and warning capabilities, experts caution that community awareness remains dangerously inadequate.

“The 2004 tsunami showed us that even distant countries can suffer massive damage,” warned Dr. Rafiq Shah, a geophysicist at the University of Karachi. “Pakistan must invest in public education, conduct regular evacuation drills, and strengthen its coastal infrastructure.”

Though climate change does not cause tsunamis, it could worsen their impact. Rising sea levels may allow waves to travel further inland, while more frequent extreme weather could hamper timely disaster response.

Awareness and Technology

Advancements like deep-sea pressure sensors, real-time satellite tracking, and AI-powered early warning systems are significantly improving response times worldwide. Yet, scientists and disaster experts agree that no technology can replace a well-informed public and coordinated emergency planning.

As tsunami alerts remain in effect across parts of the Pacific, the latest quake off Russia’s coast is a stark reminder that tsunamis, though infrequent, wield immense destructive power and demand constant vigilance, particularly for vulnerable coastal nations like Pakistan.