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As a tsunami leaves the deep waters of the ocean and travels into the shallower waters near the coast, it transforms. Since a tsunami travels at a speed that is related to the water depth, thus, as the water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both its wave speed and height, remains nearly constant. Consequently, as the tsunami's speed diminishes as it travels into shallower water, its height grows. Because of this, a tsunami, indistinct at sea, may grow to be several meters in height near the coast. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore. As a tsunami approaches shore, it slows down and grows in height. Like other water waves, tsunamis lose energy as they rush onshore. Part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through friction and turbulence. Despite these losses, tsunamis still reach the coast with a lot of energy. Tsunamis have great erosional potential, and can remove sand from the beaches that have taken years to accumulate and also undermine trees and other coastal vegetation. Capable of flooding hundreds of meters inland past the typical high-water level, the fast-moving water associated with the flooding tsunami can crush homes and other coastal structures. Tsunamis may reach a maximum vertical height onshore above sea level, often called a runup height, of 10, 20, and even 30 meters. Back (Characteristics of a Tsunami) | Next (Difference between Tsunami and other waves) |