Completely unrelated events. A typhoon is a storm — a tropical cyclone in the northwest Pacific, made of wind and rain. A tsunami is a series of ocean waves, almost always caused by an undersea earthquake, and it has nothing to do with weather. Typhoons are atmospheric; tsunamis are seismic.
The core difference
- typhoon — a weather system: a rotating tropical storm with sustained high winds, the northwest Pacific name for what the Atlantic calls a hurricane.
- tsunami — a geological event: waves generated by the sudden displacement of a large volume of water, usually by an undersea earthquake, and also by landslides, volcanic eruptions or, in principle, impacts.
They are confused mainly because both arrive from the sea and both cause coastal flooding. The causes have nothing in common.
How a tsunami behaves
In deep water a tsunami is barely noticeable — a long, low wave crossing the ocean at the speed of a jet aircraft. It only becomes destructive as it reaches shallow water, where it slows and its energy is forced upward. That is why ships at sea can be unaware of one passing beneath them while the coast is devastated.
It is also a series of waves, not one, and the first is often not the largest — which is why the danger persists long after the initial arrival.
Why "tidal wave" is misleading
Tidal wave was the old English name and it is inaccurate: tides are driven by the gravitational pull of the moon and sun, and have nothing to do with the mechanism. Tsunami — Japanese for "harbour wave" — has largely replaced it in careful use.
Storm surge, which is the genuine overlap
A typhoon does raise sea level and flood coasts, through a storm surge: water pushed ashore by wind and low pressure. A surge is meteorological and a tsunami is seismic, but the damage can look similar, which is the root of most of the confusion.
Frequently asked questions
Is a typhoon the same as a tsunami?
No. A typhoon is a storm made of wind and rain; a tsunami is a series of ocean waves caused by an undersea earthquake or similar displacement. They are unrelated.
Why is "tidal wave" wrong?
Tsunamis have nothing to do with tides, which are driven by the moon and sun. Tsunami, Japanese for "harbour wave", is the accurate term.
What is a storm surge?
Coastal flooding caused by a storm pushing water ashore through wind and low pressure. It is meteorological, unlike a tsunami, though the damage can look similar.