Evidence drawn from the long-term geological history of a volcano can rarely contribute to short-term prediction of a particular event. Only very general prophesies are possible from such an approach, though these are by no means without value. Geological study gives perspective to the historic record, creating a more realistic awareness of a volcano's potential and providing a constraining background for planning and further development around the volcano. Since volcanoes tend to have somewhat individual characteristics, in the event of an eruption it is important to have some knowledge of the previous history and behaviour as a possible guide to the come that the current eruption may take. In many instances precedents are available from well-documented historic eruptions but this is not always so and it is often necessary to rely upon geological evidence of prehistoric activity. Very occasionally the detailed reconstruction of short-term events from the geological record and the recognition of past patterns of activity may allow comparisons to be made with the current situation and have some predictive value.