surges occur in association with tropical cyclones, the phenomenon is not confined to the tropics alone. Any low-lying coastal region may experience storm surge when a deep depression over the sea accompanied by strong winds, approaehes the shore. The most vulnerable parts of a coastline lying in the path of tropical cyclones are bays and shallow estuaries. To assess the hazard it is necessary to make a frequency analysis of storm surge heights along different sections of vulnerable coastlines, and to consider, in addition, the possible combined effects of the meteorological surge and the astronomical tide. Confidence in the assessment of the hazard will depend greatly on the quality of the data received.* 5.5 Avalanches The estimation of avalanche hazards is based on studies of past records of avalanche events and also, on climatological data and terrain conditions. However, it should be stated that ava- lanche hazard assessment is extremely difficult because there is no accepted theory of avalanches, and little is known about the mechanism that triggers them. A great deal remains to be learned about the interaction of weather, terrain and snow conditions. 5.6 Landslides The subject of landslides is discussed in greater detail in Section VI, in conjunction with earthquakes. However, consideration should also be given to the possibility of landslides where heavy rains and floods may occur. Landslides hazard is difficult to estimate as an independent phenomenon. It seems appro- priate, therefore, to associate landslides with other hazards such as tropical cyclones, severe local storms and river floods. This consideration is clearly obsemed in countries which, for the purpose of preventing or mitigating flood damage, also adopt measures to prevent hillside erosion and landslides. *For more detailed discussion of data requirements, reference should be made to Publication No. 500: Present Techniques of Tropical Storm Surge Prediction. Report on Marine Science Affairs, No. 13, 1978. Set- 
**Analysis**
The text appears to be discussing natural hazards and risks, such as storm surges, avalanches, and landslides, and how to assess and mitigate them. The language used is technical and scientific, suggesting that the text is focused on a specific field of study or profession. The mention of publications and references also suggests an academic or professional context.

**Category**
Natural resources and environment, Science and technology