Question

Чем объяснить, что высота цунами в открытом море небольшая, но может значительно увеличиваться у берега?

Answer 1

Если бросить камень в центр большой лужи, то от него пойдут круги - представили. Первый круг - в виде круговой волны будет самый высокий
и он имея какую-то скорость будет стремительно удаляться от центра, все время увеличивая свой радиус. Но это поверхностные волны - вся их энергия сосредоточена на поверхности воды - в лучшем случае энергии волны хватит чтобы переместить спичку.
Другое дело если волна внутренняя - создалась на дне или в толще воды. В этом случае к берегу пойдет незаметная маленькая поверхностная волна, но вся энергия волны будет внутри - в более нижних слоях. И внешне не чем не примечательная волна движущаяся по поверхности, при подходе к берегу и подпитываемая из глубины, (Слон плывет - мы видим уши.) ведет себя по другому, чем обычная волна. Такая волна набежав на берег не может отхлынуть обратно как обычная волна, так как она будет подпитываться изнутри.

Answer 2

Explanation of the Difference in Tsunami Height in Open Sea and at the Coast

The height of a tsunami in open sea is generally small compared to its height when it reaches the coast. This difference can be explained by several factors:

1. Shoaling Effect: As a tsunami approaches the coastline, the ocean floor becomes shallower, causing the wave to slow down and compress. This compression leads to an increase in wave height. The shoaling effect is particularly significant in areas with a steep continental shelf or underwater canyons.

2. Convergence of Wave Energy: When a tsunami wave approaches the coast, it encounters the resistance of the shallow water and the friction of the seabed. This causes the wave to slow down further and the energy to concentrate, resulting in an increase in wave height. The convergence of wave energy can amplify the tsunami's impact on the coast.

3. Refraction: As a tsunami wave approaches the coast, it encounters variations in the shape of the coastline and underwater topography. This leads to the bending or refraction of the wave, causing it to focus its energy on certain areas. Refraction can result in localized areas of increased wave height along the coast.

4. Reflection: When a tsunami wave reaches the coast, it can be partially reflected back into the open sea. This reflection can cause the wave to interact with incoming waves, leading to the formation of standing waves or amplification of the initial wave height. Reflection can contribute to the increase in tsunami height at the coast.

It is important to note that the specific characteristics of a tsunami, such as its initial size, shape, and energy, as well as the coastal geography and bathymetry, can also influence the difference in tsunami height between open sea and the coast. Additionally, local factors such as coastal structures and vegetation can further modify the impact of a tsunami at the coast.

Conclusion

In summary, the height of a tsunami in open sea is relatively small compared to its height when it reaches the coast. This difference can be attributed to the shoaling effect, convergence of wave energy, refraction, and reflection. These factors, along with the specific characteristics of the tsunami and the coastal geography, contribute to the significant increase in tsunami height at the coast.