question: What makes tsunamis dangerous? answer: They can cause flooding paragraph: Not all waves are caused by winds. A shock to the ocean can also send waves through water. A tsunami is a wave, or set of waves, that is usually caused by an earthquake. As we have seen in recent years, the waves can be enormous and extremely destructive. Tsunamis can travel at speeds of 800 kilometers per hour (500 miles per hour). Usually tsunami waves travel through the ocean unnoticed. Tsunami waves have very small wave heights. In contrast, they have very long wavelengths. If you were at sea, you would not notice it pass under your ship. But when they reach the shore they become enormous. Tsunami waves can flood entire regions. They destroy property and cause many deaths. 