|You have just taken off on a jet from Anchorage, Alaska bound for Hawaii. At the same time a terrible underwater earthquake occurs off the coast of Alaska. Lucky you! As you relax in the jet, there is something moving through the ocean below you at around the same speed (about 450 miles per hour). It is a special type of wave generated by the underwater earthquake called a tsunami wave. The earthquake pushes the ocean floor up, and the water above it. This causes a wave to be generated on the ocean surface. Itís like when youíre getting into the tub. If you gently ease yourself in, you donít disturb the water surface too much. However, if you sit down very quickly, you cause big waves that can splash the water out of the tub. The tsunami wave transports the energy from the earthquake (called seismic energy) away from the initial site through the backward and forward motions of the water. Will the wave reach Hawaii at the same time as you? In fact, no. As the wave travels through the ocean, the shape of the ocean floor can direct the wave in a different direction altogether, as well as cancel out the waveís energy. However, if the conditions are just right, the wave can carry a substantial amount of the initial seismic energy toward Hawaii. As the wave enters the shallower water off the coast of Hawaii, the friction from the oceanís bottom causes the wave to slow down substantially. This is where the makeup of the ocean floor really causes the wave to do one of two things. It can run ashore as a tidal flood, causing typical flood damage. It can also build into a single, gigantic wave that can exceed heights of 100 feet as it comes crashing onto the shore of Hawaii. So, as you settle in at your hotel in Hawaii you may be in for quite a shock, and you might want to look for a high place to stay when you go to Hawaii!
I am the director for the Tsunami Inundation Mapping Efforts at the Pacific Marine Environmental Laboratory in Seattle. Basically, my job is to find ways to detect tsunamis so that we can minimize the death toll and property damage sustained by high-risk areas. We are working on a system to detect tsunami waves while they are in the deep ocean so that we will have warning as to when and where a tsunami might strike next. The system consists of a network of six deep-ocean stations that can track tsunamis and report them in real time, a project known as Deep-Ocean Assessment and Reporting of Tsunamis (DART). The difficulty in detecting a tsunami wave is that it may only be a few yards high on the oceanís surface; however, the length of the tsunami wave can extend hundreds of miles into the open ocean. This makes a tsunami wave very difficult to detect, especially from above the surface of the ocean. So weíve placed recorders at the bottom of the ocean that can detect a change of pressure, signifying a large, possible tsunami, wave passing by it. The detectors will then inform a buoy at the oceanís surface when it detects a tsunami, which in turn sends a signal to a satellite up in orbit around the earth. The information is relayed to officials who will sound an alarm to high-risk places where the tsunami poses a threat. I am also involved in educating people in high-risk areas of the potential danger they constantly live in, with the hope of making it possible for DART to be a successful endeavor.