Landslides, as secondary hazards, are often triggered by heavy precipitation. Areas with medium to steep slopes become oversaturated and failure occurs along the weakest zones. Thus, low-lying valley areas are not the only sites vulnerable to precipitation. Chapter 10 is devoted to this phenomenon.

c. Storm Surge

A storm surge is a temporary rise in sea level caused by the water being driven over land primarily by the on-shore hurricane force winds and only secondarily by the reduction in sea-level barometric pressure between the eye of the storm and the outer region. A rough relationship between atmospheric pressure and the storm surge level was shown in Figure 12-3. Another estimate is that for every drop of 100 millibars (mb) in barometric pressure, a 1m (3.28 feet) rise in water level is expected. The magnitude of the surge at a specific site is also a function of the radius of the maximum hurricane winds, the speed of the system's approach, and the foreshore bathymetry. It is here that the difficulty arises in predicting storm surge levels. Historical records indicate that the increase in mean sea level can be negligible or can be as much as 7.5 meters (24.6 feet) (ECLAC/UNEP, 1979). The most vulnerable coastal zones are those with the highest historical frequencies of landfalls. Regardless of its height, the great dome of water is often 150km (93 miles) wide and moves toward the coastline where the hurricane eye makes landfall.

Country	Year/Month	Casualties	People Affected	Damage thousands/ us$	Hurricane name	Source
Nicaragua	1971 09	35	2,800	380	Edith	OFDA
	1988 10	120	300,000	400,000	Joan	OFDA