Consider the following statements about Tsunami: 1. The speed of Tsunami waves depends upon the depth of water. 2. All earthquakes and volcanoes that occur on the sea floor lead to the formation of Tsunami. Which of the statements given above is/are correct?

• Earthquakes and volcanic eruptions that cause the sea-floor to move abruptly, resulting in sudden displacement of ocean water in the form of high vertical waves, are called Tsunamis (Harbour Waves) or seismic sea waves.
• It should be noted that only those earthquakes, which have high magnitude and which cause the ocean floor to move up and down, lead to Tsunami events.
• Normally, the seismic waves cause only one instantaneous vertical wave; but, after the initial disturbance, a series of after waves are created in the water, that oscillate between high crest and low trough, in order to restore the water level.
• The speed of wave in the ocean depends upon the depth of water.
• It is more in the shallow water, than in the ocean deep. As a result of this, the impact of Tsunami is less over the ocean and more near the coast, where they cause large-scale devastations.

Therefore, a ship at sea is not much affected by Tsunami and it is difficult to detect a Tsunami in the deeper parts of the sea. It is so, because over deep water, the Tsunami has very long wave-length and limited wave-height.

• Thus, a Tsunami wave raises the ship only a metre or two, and each rise and fall takes several minutes.
• As opposed to this, when a Tsunami enters shallow water, its wave-length gets reduced and the period remains unchanged, which increases the wave height.
• Sometimes, this height can be up to 15 m or more, which causes large-scale destructions along the shores. Thus, these are also called Shallow Water Waves.
• Tsunamis are frequently observed along the Pacific Ring of Fire, particularly along the coast of Alaska, Japan, Philippines, and other islands of south-east Asia, Indonesia, Malaysia, Myanmar, Sri Lanka and India etc.