一 寸 光 阴 不 可 轻 1 Today, our lecture is about tidal waves. Ill define what a tidal wave is and what a tidal wave is not. Ill also define some other terms related to tidal waves. So, what is a tidal wave? A tidal wave is a very large and very destructive wall of water. This wall of water rushes in from the ocean toward the land. Scientists use the Japanese word ”tsunami” to describe this waves. In Japanese, tsunami actually means harbor wave, you see the waves are tallest when they reach a harbor which is an area of the ocean just before the land where boats are kept. Now, normal waves are caused by tides or storms over the water. But did you know that tidal waves are not caused by storms and that tidal waves are not really tides at all? A true tide can be defined as the regular rise and fall of ocean waters at definite times each day. A tidal wave or tsunami comes rushing in suddenly and unexpectedly at any time. It could come rushing in during the morning, in the afternoon or during the night. A tidal wave is caused by an underwater earthquake, to quake means to move up and down or from side to side very quickly, to quake also means to shake or to tremble, when an earthquake takes place under the ocean, the ocean floor shakes and trembles, and sometimes the ocean floor shifts. That is the ocean floor moves. It is the shifting of the ocean floor that produces the tidal wave. The earth and water move, causing a tidal wave. The tidal wave begin to move across the sea at great speed. In XXXX, a massive earthquake occurred of the coast of Japan, the quake caused a double wave tsunami. A double wave tsunami can also be called a merging tsunami. When a merging tsunami or double-wave tsunami occurs, two very large waves combined. This increases the destruction when the tidal wave reaches land. Tsunamis have taken many lives in the past, for instance, the tsunami caused by a 9.0 magnitude earthquake off the coast of Japan on March 11,XXXX, took the lives of more than 20 thousand people. The tsunami also destroyed large areas of northeastern Japan. Today, scientists can predict that a tidal wave will hit land, these scientists use a seismograph, a seismograph is a type of instrument that recalls the strength, direction and length of an earthquake. The seismograph tells the scientists if the earthquake under the ocean is likely to cause a tidal wave. So although it is not possible to stop a tidal wave, its possible to warn people that a tidal wave is coming. This warning can save many lifes.