A tsunami is a large and long wave caused by volcanic activity or an earthquake. Tsunami’s can be generated by actions across an ocean that trigger a ripple of growing waves. In the open sea, the tsunami’s height and affect are not nearly as dramatic as they approach coastal regions and islands. Tsunamis are extremely powerful and dangerous with the ability to travel up to 10 miles inland.
What a Tsunami Is
Tsunami’s are triggered when a massive amount of land is displaced akin to a brick being dropped in a bucket of water. Tsunami triggers are most often earthquakes or volcanic eruption but may also be caused my meteorite landing or calving icebergs, though these are rare. In deep waters, tsunamis travel up to 500 miles per hour but slow as their height increases to over 32 feet in coastal waters.
The word tsunami comes from the Japenese words, tsu for harbor and nami for wave. Unlike the 40-foot monster waves that surfers dare to tackle, tsunamis’ length push them farther into coastal regions with dramatic, powerful pullback and undertow as the water recedes back to the ocean depths.
Where Tsunami’s Occur
Tsunamis can occur in any coastal area exposed to the ocean. While they have been reported in the Mediterranean Sea, Atlantic Ocean and Indian Ocean, they are most prevalent in the Pacific Ocean. More than 59% of the world’s tsunamis have occurred in Pacific waters throughout islands, coastal cities bays.
The Mediterranean and Carribean both have subduction zones, areas where tectonic plates have crashed resulting in frequent earthquake activity. These makes them susceptible to tsunamis.
Is a Tidal Wave a Tsunami?
A tidal wave and a tsunami are two different types of ocean occurrences. While many often use the terms interchangeably, a tidal wave is a regularly occurring large wave resulting from gravitational interactions between the sun, moon and earth. In other words, tidal waves are extremely robust tides with large waves. Tsunamis are not related to tidal activity at all.
When Tsunami’s Are Likely to Occur
Tsunamis can occur with little to no warning. In 2004, a Christmas Day massive earthquake registering 9.1 on the Richter Scale struck offshore of Sumatra, Indonesia. Within minutes, a series of massive 100-foot waves lead to one of the deadliest natural disasters in history, killing more than 227,000 people in 14 different countries. From the moment of the earthquake to the waves breaching the shores, there are merely minutes.
Other triggered tsunamis travel the ocean. For example, earthquakes in Japan often trigger tsunami warnings across the Pacific as far as Mexico and the US West Coast. The Deep-Ocean Assessment and Reporting of Tsunamis (DART) system is a network of deep-sea buoys that measure water displacement across the ocean to determine tsunami occurrences and path. This system gives distant coastal communities such as Hawaii, the Cook Islands and continental coasts the ability to evacuate and plan for disaster.
Signs of a Tsunami
While a tsunami may occur very quickly after a seismic event, there are often warning signs. It is important to react quickly if you feel a tsunami is approaching; you can’t outrun the powerful waves. Often, when a tsunami follows immediately after an earthquake, people are still trying to react to the earth movement.
In 2011, Japan experienced a magnitude 9.1 Richter Scale devastating earthquake with massive destruction. Within minutes, the entire region was hit with a tsunami and its towering 133-foot waves. There was simply not time to react.
The signs of a tsunami are:
- An earthquake: experiencing earthquake activity in coastal areas is the first alert that a tsunami may approach
- Shoreline waters recede: water is sucked out to sea and accumulated in the tsunami wall. Reefs are exposed with boats and fish remaining stranded
- Load roar: as the tsunami approaches shore, it may sound like a train or aircraft moving through
- Rising horizon: the line in the distance where the sky meets the sea becomes higher as the wave approaches
- Tsunami alarms: some coastal areas have installed large networks of warning systems to let coastal communities know to evacuate for an incoming tsunami
What to Do in a Tsunami
You cannot outrun a tsunami. People may find the phenomenon of the receding water intriguing. In fact, there are pictures of old coastal towns where people run out to the reefs to collect fish. This is the last thing you should do. When the waves come, they will be fast, large and like river rapids pulsing through streets and inland areas.
Here is what to do if a tsunami is approaching:
- Stay off the beach
- Head inland
- Seek higher ground away from the coast and rivers
- Heed all alarm warnings and emergency personnel
If you don’t have warning, you need to do what you can to stay above the water as long as possible. Indonesian residents and tourists were captured on video climbing palm trees and balconies to stay as high as possible. The water receding is as dangerous as it coming in.
There isn’t one great big wave. It is a series of waves that come in sets. Think about surfers waiting for the next set with a lull in between. The tsunami will come in similar fashion. Don’t return to shore communities until you have been given the all clear from authorities.
What If I’m in a Boat and a Tsunami Strikes?
If you are in a boat, you will need to get out to deeper water if at all possible. The target depth is greater than 100 meters. The deeper you go out into the open ocean, the less displacement there is of water. This means the tsunami waves are smaller. However, if you are close to shore or in the dock, it is best to moor the boat and head to higher ground. Stay tuned to mariner reports.
Surviving a Tsunami
Surviving a tsunami is directly related to how much time a person has to react. In 1960, a magnitude 9.5 earthquake hit Chile. Many survived the actual earthquake. Those who fled to higher ground immediately were saved. The earthquake triggered a tsunami that also travelled across the Pacific to Hawaii where the small bay town of Hilo devastated.
The warning systems were not effective and many residents returned to their homes after the first series of waves only to be killed by the next series. Growing up in Hawaii, I’ve heard stories of the destruction to Hilo from the 1960 Chilean tsunami. My paternal grandfather showed us the marks on the buildings that still showed how high the water came.
The Sets Continued to Come
That tsunami’s first wave was approximately 4-feet just after midnight. Just before 1 am, a second set came in double in size. The third set came in just after 1 am with waves exceeding 14-feet. Sets continued past 2 am.
On my maternal grandparents’ side, I had heard stories of beach dwellers waiting at their patio homes to watch securing themselves with straps to the patio beams. The extensive reef system seemed to temper the waves there. In fact, the National Tsunami Center sits within a mile from my grandmother’s southern shore home, situated there because a tsunami never crossed the street, some 200 yards from the shoreline.
Final Thoughts on Tsunamis
When a large wave heads to shore, you may not have time to react. Move quickly and get to higher ground immediately. Anytime you experience an earthquake near a coastal region, assume there is a strong chance for a tsunami to follow. What you do in those few minutes could save your life.
Be Safe Smart