Wind‑generated waves only cause water movement near the surface, while tsunami waves result from the movement of the water from the surface to the sea floor. The speed of tsunami waves depends on the water depth. Unlike in the case of wind‑generated waves, the deeper the water, the faster the waves. Tsunami waves slow down in the shallow water, near the land. But because the energy they carry is still the same, the energy causes the waves' amplitude to rise. Volcanic activity can lead to the formation of tsunamis in several ways. The eruption of an underwater volcano can generate energy which creates the tsunami wave. This happens when hot magma explodes in contact with cold seawater. However, the impact that can generate a tsunami wave can also come from a landslide triggered by the eruption of a coastal volcano.

Iceberg calving is an event when chunks of ice break from the edge of the main ice mass. As the chunks can be enormous and weigh hundreds of thousands of tons, the energy released at the moment of their collapse into the water can trigger tsunami waves. Since climate change causes increased melting of the Earth’s ice caps, calving is becoming a more and more common occurrence.

Large earthquakes on the seafloor are the most common causes of tsunamis. Movement of tectonic plates can result in an abrupt rise or fall of the Earth's crust, which in turn releases energy that pushes the water up to the surface. When the water rises above the standard sea level, it falls gravitationally and splits into tsunami waves that disperse in different directions from the epicentre.

A wave has its crest, the top part, trough, the bottom part, and amplitude, which is the distance between the sea level and the crest or trough. If the tsunami's trough reaches shore first, an interesting phenomenon occurs. The water suddenly retreats and exposes the seafloor. It’s crucial to know that it is a very important warning sign pointing out that a tsunami is coming. It usually gives people only a couple of minutes to move as far from the coast as they can, or at least to higher ground. The wave's crest usually hits shore about five minutes later.

Indian Ocean Earthquake and Tsunami, December 26th, 2004. It’s been categorised as the deadliest tsunami recorded in history. The waves which hit Sumatra, Thailand, Sri Lanka, and many other locations around the Indian Ocean were triggered by a 9.1 magnitude earthquake and reached 50 metres. The effect was hundreds of thousands of deaths, many of them tourists spending their Christmas in the region, thousands of local people displaced from their homes, and billions of dollars in damage.

Tōhoku Tsunami, Japan, March 11th, 2011. The 10‑metre high waves were triggered by a magnitude‑9 earthquake . It was the strongest earthquake in Japan’s recorded history. Apart from levelling more than 100,000 buildings and claiming almost 20,000 deaths, it caused a nuclear disaster. The defences were not strong enough to prevent the gigantic wave from flooding the plant. Three reactors in the Fukushima Daiichi nuclear power plant melted down, releasing radioactive discharge. Over 150,000 people were evacuated from the area and haven’t returned till today.

Krakatoa Eruption and Tsunami, May 20th, 1883. Krakatoa, a volcano situated on an island near Sumatra, exploded on August 27, 1883. It was heard 3,000 miles away. The eruption threw five cubic miles of earth 50 miles into the air, which led to a so‑called volcanic winter. In the four years after the explosion, winters worldwide were exceptionally cold with frequent blizzards and heavy snowfalls. It also triggered an almost 60‑metre‑high tsunami wave whose impact was felt as far as South Africa. Krakatoa is still active, and it is predicted to erupt again in the future, causing more tsunamis.

Apart from constructions aimed at lessening the impact of tsunami waves, such as seawalls and sea gates, or channels which are supposed to collect and divert the water away from the main infrastructure, people in the regions most afflicted by tsunamis started to build houses designed to resist forceful waves. One of the solutions in such buildings is building up in order to provide a chance for the inhabitants to escape the wave to higher floors of the buildings.

CWarn is an international organisation which constantly monitors seismic activity around the world. It has a global tsunami warning and alert system. Countries which want their citizens to be informed via a text message about a potential danger have to register with the system, but membership is free of charge. Registered members are sent text messages, including information about the earthquake magnitude, time, date, location, and threat level.