The main characteristics of tsunamis include:

1. Triggering Event: Tsunamis are usually caused by underwater earthquakes, volcanic eruptions, or landslides. These events displace large amounts of water, creating powerful waves.

2. Speed and Energy: Tsunamis can travel at high speeds, often exceeding 500 miles per hour (800 kilometers per hour) in deep ocean waters. This allows them to cover vast distances and retain their energy over long periods.

3. Wave Height: While tsunamis may not appear as towering waves in the open ocean, they can grow significantly in height as they approach shallow coastal areas. This is due to the compression of the wave energy, resulting in a sudden increase in wave height.

4. Long Wavelength: Tsunamis have long wavelengths, which means that the distance between successive wave crests can be several tens or hundreds of kilometers. This characteristic allows them to travel across entire ocean basins without significant loss of energy.

5. Destructive Power: Tsunamis possess immense destructive power due to their large volume of water and high energy. They can cause widespread flooding, damage infrastructure, and result in loss of life and property.

6. Warning Signs: Prior to the arrival of a tsunami, there may be some warning signs such as the rapid retreat of water from the shoreline, unusual ocean behavior, or the sound of an approaching train. However, these signs may not always be present, making it crucial to have early warning systems in place.

7. Multiple Waves: Tsunamis often arrive in a series of waves, with the first wave not necessarily being the largest. This can lead to a false sense of security if people assume that the danger has passed after the initial wave.

It is important to note that tsunamis can vary in their characteristics depending on the specific circumstances of each event.