big floods
Tsunamis do not affect the atmosphere.
If a large meteor or asteroid were to strike in a sea or ocean, it could certainly cause a large tsunami. We have no records of this occurring recently, although it almost certainly has happened in the distant past.
Tsunami's happen most around the Pacific ocean because that's where the worlds tectonic plates are situated, so when one shifts, it often results in a Tsunami...
Tsunamis typically occur in oceanic regions with tectonic activity, such as the Pacific Ring of Fire. This includes areas like the coastlines of Japan, Indonesia, Chile, and the western United States. Tsunamis can also be triggered by underwater volcanic eruptions or landslides.