The Earth Story

Storytelling Tradition Saved Lives in Boxing Day Tsunami Memorials to those who died in the tsunami on Indonesia’s Banda Aceh do more than offer remembrance; they also provide an education tool to teach school children about tsunamis and to recognize the warning signs. After the Boxing Day earthquake, many people went to the beaches when the waters receded instead of going to higher ground, which cost them their lives. It is a much different story on Indonesia’s island of Simeulue, where 7 people died out of a population of around 70,000. Simeulue is located just 50 kilometers from the epicenter where the 9.2 magnitude earthquake hit. The island received no warning that the tsunami was coming. Simeulue has suffered through earthquakes and tsunamis in the past, and an oral tradition called “smong” developed. Grandparents in particular teach their grandchildren the smong which concludes with, “If a strong tremor occurs, and if the sea withdraws soon after, run to the hills, for the sea will soon rush ashore.” The people on Simeulue’s coast remembered this lesson and ran to the island’s hills, thereby saving their lives. It is hoped that educating school children in Banda Aceh will ensure that they too will know what to do if a tsunami ever happens again. - RE Photo Credit: Tsunami damage in Sumatra by U.S. Navy photo by Photographer's Mate 2nd Class Philip A. McDaniel http://bit.ly/16QHYrM Read More:  http://www.bbc.com/news/magazine-30542317?OCID=fbasia http://unesdoc.unesco.org/images/0018/001831/183133e.pdf

Tsunami wave propagation

This video, produced by the Tectonics Observatory at Caltech, shows a simulation of how the 2004 Tsunami worked its way through the Indian Ocean. You can see which features cause it to bend, slow, or stop, and which features take direct hits. You can also see how there are peaks and troughs formed by the waves as they spread out from the source.

Simulations like these, conducted on modern supercomputers, allow scientists to understand how tsunamis move after they’re generated and allow policy-makers and emergency preparedness organizations a better understanding of how their risks are impacted by different geologic scenarios.

-JBB

Video credit: TO https://www.youtube.com/watch?v=N95rsXj0jDU

Read more: http://nctr.pmel.noaa.gov/propagation-database.html

On Tsunami Waves

This infographic illustrates the basic principles behind the formation and movement of tsunami waves – on the 10th anniversary of the disastrous 2004 Indian Ocean tsunami this seemed like a good reminder.

A tsunami wave forms when things move up or down beneath the ocean, most commonly when a fault breaks in a large earthquake. If either a thrust fault or a normal fault breaks, rocks will move up and down. Compared to the weight of the rocks in Earth’s crust, the weight of ocean waters on top are tiny, almost completely negligible. The crust thrusts the waters upwards or pulls the waters downward as the fault breaks, creating a wave. 

The wave, either up or down, propagates outward from that spot, carrying energy with it. When a thrust fault breaks, it’s kind of like a giant pile of water getting out of the way; it races out in all directions.

When the energy from the tsunami gets close to shore, the waves pile up, slowed at the base by the friction between the flowing water and the rising ocean floor. As the waves pile up, their height increases and the energy of the waves are concentrated, bringing them up against the shore with potentially huge forces. 

Sometimes the trough, the downward part of the wave, will arrive first, causing the ocean to seemingly retreat, but this doesn’t happen every time and it depends on the exact motion of the fault. 

There can be other ingredients in tsunami waves, including undersea landslides, bending of waves around coastlines, and amplification of wave heights at high tide, but those are the basic processes involved in an event like the 2004 Indian Ocean disaster.

-JBB

Image credit: http://en.wikipedia.org/wiki/Tsunamis_in_lakes…

Read more: http://www.tsunami.noaa.gov/basics.html

Bending a wave One of the many scientifically interesting things about the 2004 tsunami was what happened on the island of Sri Lanka.  Sri Lanka sits just across the Indian Ocean from Sumatra and was right in the path of the tsunami; the eastern sides of the island took a direct hit and there were thousands of casualties. But that wasn’t the only part of the island hit; the waves actually hit the backside of the island as well. Tsunami waves behave like other wave types in that they don’t travel in straight lines. In the case of Sri Lanka, as the waves approached the island, the parts of the wave exposed to the coastline slowed down while the parts in deeper water continued traveling at their same pace. This caused the wave energy to bend around the southern edge of the island, slamming into the portions that didn’t face Sumatra.  On the southwestern coast of Sri Lanka, more than 1000 people were traveling on a loaded train between Colombo and Galle as the tsunami hit. That train was hit by waves that were over a meter taller than the top of the train. It was pushed inland, drowning many of the passengers as well as passers-by that climbed on top of the train hoping for safety. That disaster only occurred because of the way the tsunami wave bent around the island. The image showing Sri Lanka’s coastline actually captured the waves as they were moving. NASA’s Terra Satellite passed over the area just as the waves were approaching and the Multi-angle Imaging SpectroRadiometer (MISR) was able to detect the waves due to the changing angle of the ocean’s surface that also changed the angle that sunlight reflected back to the satellite. -JBB Image credits:  https://eosweb.larc.nasa.gov/sites/default/files/project/misr/gallery/tsunami_sri_lanka.jpg http://www.thelongacre.net/2011/03/tsunami-where-you-at.html Read more: http://www.bom.gov.au/tsunami/info/ http://bit.ly/13Bw2bs http://news.bbc.co.uk/2/hi/south_asia/4132247.stm http://sciencelearn.org.nz/Science-Stories/Tsunamis-and-Surf/Behaviour-of-waves

When the waters retreated Today is December 26, 2014. I had to write out the date because the day after Christmas is locked in my memory from what happened 10 years ago.  Just before 8:00 a.m. local time, the earth’s crust off the western coast of the island of Sumatra broke. The crack started near Sumatra and propagated a huge distance to the North, over 2000 kilometers. The ground shook violently and so much energy was released that the entire planet bent and swelled for days afterwards.  The incredible shaking was only the smallest part of the disaster. On the floor of the ocean where the crack formed, areas where the crack reached the surface were pushed upward, in some cases by as much as twenty meters. That rupture lifted up the ocean waters into a giant pile that the waters flowed away from as a series of giant waves – a tsunami.  A few minutes after the shaking stopped, this spot was hit by waves tens of meters high. The upper image shows Banda Aceh, the closest community to the quake’s epicenter, after the quake in 2004.  The tsunami wave was a slow-motion disaster. It moved across the Indian Ocean over several hours, striking people in Sri Lanka, Thailand, and India who received no warning. It even hit the continent of Africa with enough force to cause damage and deaths on the other side of the ocean. Over 225,000 people were killed, making the quake estimated to be the 5th deadliest earthquake in recorded human history. Much has changed in the 10 years since this disaster. As you see in the second photo, taken recently on the same spot, many communities have rebuilt from the damage. The debris and pollution spread by the tsunami has mostly washed away. That day likely still leaves scars on the survivors and memories of those who were lost, but the outward scars seen around the ocean in the following days have mostly healed. The earth science community and the world also were changed by the tsunami. In 2004, tsunami science was thought of as important, but there wasn’t a recent event to spur work in that field. By some estimates, since 2004 the number of researchers working on tsunamis has multiplied by a factor of 10. Those scientists have made some remarkable findings, such as ways to build structures able to survive the waves, predictions of tsunami heights depending on earthquake locations and energies, and how to interpret geologic records of tsunami as evidence of earthquakes across the ocean. But even with that progress, the overtopping of sea walls by the Japanese tsunami in 2011 still shows that we have work to do.  The most tangible evidence of a response to the 2004 quake can be found in tsunami preparation. In 2004, the only tsunami warning office in the world was the Pacific Tsunami Warning Center. It had a staff of 8, would close for part of the day, and had access to 6 tsunami-monitoring buoys. Today, the Pacific Tsunami Warning Center has a staff of 15, is open 24 hours a day, 7 days a week, and controls a network of 60 tsunami-monitoring buoys. The Pacific system also helped Australia, India, and Indonesia establish a warning system in the Indian Ocean, which opened in 2006 and is gradually improving its capabilities and being linked to at-risk coastal communities.  Had these systems been in place in 2004, they literally could have saved hundreds of thousands of lives. Perhaps that is one positive legacy of this disaster worth remembering today, 10 years later, as we look back on the recovery of those communities. Image credit: AFP/AP/Getty http://www.theguardian.com/world/gallery/2014/dec/11/then-and-now-the-aftermath-of-the-2004-indonesian-tsunami-in-pictures Read more: http://earthquake.usgs.gov/earthquakes/world/most_destructive.php http://www.nsf.gov/news/news_summ.jsp?cntn_id=106726 http://news.yahoo.com/scientists-strides-tsunami-warning-since-2004-155016481.html http://www.gns.cri.nz/Home/Our-Science/Natural-Hazards/Tsunami/2004-Boxing-Day-Tsunami http://www.bbc.com/news/world-asia-30572079 http://portal.unesco.org/en/ev.php-URL_ID=33442&URL_DO=DO_TOPIC&URL_SECTION=201.html http://soundwaves.usgs.gov/2005/02/