How do tsunamis occur?

 LI: I am  learning to write an explanation


Introduction
A tsunami is a series of waves that comes speeding on to the coastline.

How and why a tsunami starts? 
A tsunami is caused by an underwater earthquake,the primary cause of a tsunami. It lifts up the sea floor then drops back down and it creates huge waves that speed up to 500 mph.

What happens next?
The water rushes on to the coastline and it can destroy houses,buildings and anything that in its way.

What happens after?
Usually after a tsunami everything could be destroyed and dozens of injured people and peoples' belongings floating in the water on the roads.

Conclusion
Tsunami usually happens near coastlines and islands.