Statement I : Tsunami is small in open ocean yet may be over 30 m high when it reaches a coastline. Statement II : Tsunamis have long wavelength and they travel across the open ocean at high speed. As they approach shore, the wavelength decreases and the wave height increases.

Statement I is true as tsunamis in the open ocean have very low amplitudes, often less than one meter, making them nearly imperceptible to ships [2]. However, upon reaching the coastline, they can reach heights exceeding 30 meters due to the shoaling effect [3]. Statement II correctly explains this phenomenon through the principles of wave dynamics and energy conservation. In deep water, tsunamis possess long wavelengths (often over 100 km) and travel at high speeds, sometimes exceeding 800 km/h [4]. As the water depth decreases near the shore, the wave speed and wavelength decrease [5]. To maintain constant energy flux, the wave amplitude (height) must increase significantly [5]. This 'bunching up' of water transforms a low-amplitude deep-sea wave into a towering coastal wave, making Statement II the correct scientific explanation for Statement I [5].

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Characteristics of Tsunami Waves > p. 33
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Normal Waves vs Tsunami Waves > p. 193
3. [3] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 8: Natural Hazards and Disaster Management > Origin of Tsunamis > p. 32
4. [4] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Normal Waves vs Tsunami Waves > p. 192
5. [5] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 15: Tsunami > Propagation of The Waves > p. 191