What are the causes and effects of tsunamis?

The typical cause is an earthquake under the ocean floor. Tsunamis can also be caused by huge landslides into bodies of water, or by the impact of a large enough meteorite into an ocean or very large body of water. These things produce a wave that shifts not just a few meters of surface water, but the entire column of water from the floor to the surface. They contain enormous amounts of energy. Tsunamis can push huge amounts of water over islands and coastal regions causing the deaths of hundreds of thousands or millions of people, and they can cause millions or even billions of dollars worth of damage. Depending on whether the leading element of the tsunami is a trough or a crest (it can be either) there may be an eerie ebbing or pulling back of the water along the shore; it must appear to observers like an unnatural pulling back of the tide. This would happen if the leading element is a trough. If you ever witness this, run with all your might; seek high ground.
underwater earthquakes, volcanic eruption or land slides
the cars will flow wherever and sometimes some houses may fall it depends on the power of the wave.Some people may drown because of the big wave... even when a person is in the water holding on to something who knows if there will be a big object flowing towards the person.