![]() The continual action of waves beating against a rocky cliff, for example, may cause some rocks to come loose. Over many years, water and wind wear away at the land. Most beach materials are the products of weathering and erosion. Materials such as sand, pebbles, rocks, and seashell fragments cover beaches. NOAA scientists are working to further improve warning center operations and to help communities be prepared to respond.A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river. ![]() Tsunami warning capabilities have become dramatically better since the 2004 Indian Ocean tsunami. They monitor networks of deep-ocean and coastal sea-level observation systems designed to detect tsunamis and use information from these networks to forecast coastal impacts and guide local decisions about evacuation. But the tsunami warning centers know which earthquakes are likely to generate tsunamis and can issue messages when one is possible. Scientists cannot predict when and where the next tsunami will strike. The 2004 Indian Ocean tsunami, for example, impacted 17 countries in Southeastern and Southern Asia and Eastern and Southern Africa. But large tsunamis can also reach distant shorelines, causing widespread damage. Tsunamis typically cause the most severe damage and casualties near their source, where there is little time for warning. Effects can be long-lasting, and felt far beyond the coastline. Large tsunamis are significant threats to human health, property, infrastructure, resources, and economies. Stay out of the tsunami hazard zone until local officials tell you it is safe, as the danger may last for hours or days. The first wave in a tsunami may not be the last, the largest, or the most damaging. ![]() They are also dangerous as they return to the sea, carrying debris and people with them. Tsunamis can be particularly destructive because of their speed and volume. Just six inches of fast-moving water can knock adults off their feet, and twelve inches can carry away a small car. Rushing water from waves, floods, and rivers is incredibly powerful. A tsunami may come onshore like a fast-rising flood or a wall of turbulent water, and a large tsunami can flood low-lying coastal areas more than a mile inland. When they strike land, most tsunamis are less than 10 feet high, but in extreme cases, they can exceed 100 feet near their source. If you do not see an evacuation route, go to high ground or as far inland as possible. Move quickly to a safe place by following posted evacuation signs. Be prepared to respond immediately to any tsunami warnings. Official and natural warnings are equally important. These include strong or long earthquakes, a loud roar (like that of a train or an airplane) coming from the ocean, and a sudden rise or fall of the sea level that is not related to the tide. There may not be time to wait for an official warning, so it is important to be able to recognize natural tsunami warnings. They may also come through outdoor sirens, local officials, text message alerts, and telephone notifications. There are official warnings issued by tsunami warning centers that are broadcast through local radio and television, wireless emergency alerts, NOAA Weather Radios, NOAA websites, and social media. Tsunami warnings come in different forms. The wavelength decreases, the height increases, and currents intensify. As a tsunami enters shallow water near coastal shorelines, it slows offsite link to 20 to 30 mph. NOAA Deep-ocean Assessment and Reporting of Tsunami (DART) systems, located in the deep ocean, are able to detect small changes in sea-level height and transmit this information to tsunami warning centers.Ī tsunami only becomes hazardous when it approaches land. Mariners at sea will not normally notice a tsunami as it passes beneath them in deep water, the top of the wave rarely reaches more than three feet higher than the ocean swell. In the deep ocean, a tsunami can move as fast as a jet plane, over 500 mph, and its wavelength, the distance from crest to crest, may be hundreds of miles. Once a tsunami forms, its speed depends on the depth of the ocean. However, tsunamis can also be caused by landslides, volcanic activity, certain types of weather, and-possibly-near-earth objects (e.g., asteroids, comets) colliding with or exploding above the ocean. According to the Global Historical Tsunami Database, since 1900, over 80% of likely tsunamis were generated by earthquakes. Most tsunamis are caused by earthquakes on converging tectonic plate boundaries.
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