Shorelines
Wave Definitions
Wave Physics
Longshore Transport
Shoreline features Erosional (mostly)
Shoreline features Erosional (mostly)
Depositional (mostly) Shoreline features Depositional (mostly)
Shoreline Erosion Breakwater
Shoreline Erosion Jetties and Groins
Shoreline Erosion Jetties and Groins
Tides
Tides Types
Tsunamis Not all earthquakes generate tsunamis. Shallow focus-near sea bottom. Must displace seafloor. Large magnitude ( > 7.5 ) Open Ocean Jetliner Speed Small Height (1-2 feet) Source: Earthquakes by Bruce A. Bolt
Tectonic earthquake-generated tsunamis The tsunami behaved very differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a small hump, barely noticeable and harmless, which generally travels at a very high speed of 310 to 620 mph; in shallow water near coastlines, a tsunami slows down to only tens of kilometres an hour but in doing so forms large destructive waves Global Security: http://www.globalsecurity.org/eye/andaman-pix2.htm
Characteristics of Tsunamis The tsunami was not a single devastating wave, but actually a succession of several ones, occurring in retreat and rise cycles with a period of over 30 minutes between each peak. The third wave was the most powerful, and reached highest, occurring about an hour and a half after the first wave. Several smaller tsunamis continued to occur for the rest of the day.
Water Recession: A Precursor Draw Down Effect From: Nature Publishing Group Kalutara Beach, Sri Lanka The first visible indication of an approaching tsunami may be recession of water (drawdown). When a tsunami is generated, a crest and trough make up the shape of the wave. Sometimes the trough reaches land first; sometimes the crest does. If the trough reaches land before the crest, observers will see a recession of the ocean water at the shore. In this tsunami, the areas to the east of the earthquake epicenter experienced recession. Reports from witnesses in Thailand say that the ocean receded just before the first tsunami waves hit, exposing several hundred meters of beach and seabed. The satellite image shows the extent to which the ocean receded between tsunami waves at Kalutara Beach in Sri Lanka. It gives a sense of phenomenon that many observed before the tsunami waves reached the shore. From: Digital Globe
Tsunami Propagation The red color is the high water and the blue color is the low water. Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines. National Institute of Advanced Industrial Science and Technology, Japan
Tsunami Damage Location: Lhoknga, Indonesia Before Tsunami January 10, 2003 The town of Lhoknga, on the west coast of Sumatra near Banda Aceh, was completely destroyed by the tsunami, with the exception of the mosque (white circular feature) in the city's center. Lhoknga faces the open Indian ocean and had no shelter from the direct tsunami waves. This area of Sumatra’s west coast is closest to the earthquake epicenter. These high-resolution satellite images, acquired by Space Imaging's Ikonos satellite, show Lhoknga before (above) and after (below) the earthquake and tsunami. Almost all the trees, vegetation, and buildings in the area were washed away. Behind the town, low-lying agricultural areas remained covered with water four days after the disaster, and sand on the nearby beaches was completely removed. After Tsunami December 29, 2004 Source: National University of Singapore
Tsunami Damage Location: Lhoknga, Indonesia Exposed bridge piers of road that washed away. Photo: Jose Borrero These photos show the strength of the tsunami waves around Lhoknga. The water was strong enough to break trees, wash away a bridge and capsize a tanker moored on the jetty. The run-up height shown by the stripped vegetation in the lower picture is measured between 20 – 30 m. This suggests a sustained flow depth of 12 – 15 m. High Water Mark Overturned ship Damage zone showing an overturned tanker, trees snapped in half, and the high water mark on islands where vegetation was stripped away. Broken Trees Photo: Jose Borrero