The given question asks us to identify which of the listed natural hazards is not considered a hydro-meteorological hazard. Let's begin by understanding what hydro-meteorological hazards are:

• Hydro-meteorological hazards are natural processes or phenomena of atmospheric, hydrological, or oceanographic nature. These include floods, tropical cyclones, storms, and snow avalanches.

Now, let's analyze each option:

1. Snow avalanche: This is a rapid flow of snow down a slope, which primarily involves meteorological factors like snowfall and temperature changes. Hence, it is a hydro-meteorological hazard.
2. Sea erosion: While this involves the ocean, it happens due to wave actions and currents, influenced by atmospheric conditions. It can be linked to hydro-meteorological activities.
3. Tropical cyclone: These are intense circular storms that originate over warm tropical oceans and are characterized by strong winds, heavy rain, and atmospheric pressure changes. They are a classic example of hydro-meteorological hazards.
4. Tsunami: Tsunamis are long high sea waves caused by seismic activity such as earthquakes or volcanic eruptions in the ocean. These are not triggered by atmospheric conditions but by geological activities, thus categorizing them as geological rather than hydro-meteorological hazards.

Based on the above explanation, the correct answer is Tsunami because it is not primarily a result of atmospheric or hydrological phenomena but rather geological events.