VOLCANOES

Most of us can conduct our daily affairs without ever having to think about volcanoes. Others live in constant threat of danger from volcanoes, and all of us are affected by them. We all know volcanoes are large, noisy, stinky, and dangerous but they are valuable to us. Many of the metals that we use; gold, copper, zinc and others are from mines discovered in the remains of ancient volcanic edifices. The heat from these ancient volcanoes percolated water through the newly formed rocks. Percolating fluids scavenge metals from rocks and redeposit them in concentrated form, on the seafloor or along faults to form rich veins. In some cases the deposits were capped by other rocks and preserved from erosion over the eons to be discovered by our civilization. In order to predict the location of a volcanic-hosted metal deposit the modern geologist has to be familiar with all aspects of volcanic rocks and volcanoes.

Particularly violent eruptions remind us that volcanoes pose a significant risk to those who live nearby them. Mt. St. Helen's in the NW US and Mt. Pinatubo in the Phillipines recently created havoc, but fortunateley the loss of humen lives about 50 and 750 respectiveley, was minimal in comparison to the total population threatened. In contrast Mt.Pelee in Martinique erupted in 1902 and completeley destroyed the city of St.Pierre. Only two people survived. The population of nearly 30,000 was killed virtually instantaneously. That eruption spawned the modern science of volcanology. Since then we have learned a great deal about the character of volcanoes and how to better to predict their behaviour. The accurate predictions given Pinatubo resulted in the evacuation of 100,000's of people, and likely the saving of many 10,000's of lives. Those responsible for the accurate prediction did a remarkable job but they admit they 'got lucky'. In contrast, in 1991 several geologists participating in a meeting on volcanic hazard and prediction were very unlikeley. While exploring and sampling the volcano Galeras in Columbia it unexpectedly erupted resulting in several fatalities, and injuries to the geologists. Clearly we do not understand volcanoes sufficiently well to consistently and accurately predict their eruptions. The study and monitoring of active volcanoes is essential if we are to avoid catastrophe around many of our population centres built close to active or dormant violent volcanooes, e.g. Naples Teneriffe, Seattle, Vancouver, ........ and on the island of Montserrat, one of the destinations on this expedition, and illustrated here.

The monitoring of volcanoes using geophysical techniques such as seismic to monitor vibrations that arise as a result of deep magma movement, or ground tilt meters that respond to the inflation of a volcano allow us in some cases to predict fairly well on short time scales e.g. weeks or days. Clearly we wish to have longer-term predictions, however the recurrence times of many volcanoes is long in comparison to human experience. Often times we have no recorded history of volcanic eruption and they surprise us, as is the case of Pinatubo and Monserrat in the Caribbean. Consequently, geologists study the distribution and age dates of rocks deposited byvolcanoes in order to deduce the history of a given volcano. But can we use this to make predictions? In other words can we turn Hutton's principle of uniformitarianism around? Is the past the key to the future? or in more familiar terms, Does history repeat itself? The answer is No history does not repeat itself, but it may come close. Although we can not predict eruptions geologists can study volcanic deposits in order to estimate their recurrence time and severity so as to estimate the likelihood and magnitude of future eruptions in the long term, say 10's - 100's of years and beyond.

Volcanic eruptions effect all of us in that they can profoundly influence climate. The winter of 1783-84 was unusually cold as was the summer of 1784 in northern Europe and much of North America. A perpetual fog caused by volcanic gas and ashes from an Icelandic eruption diminished the amount of sunlight received at the surface. Similarly the eruption of Tamboro in Indonesia in 1815 caused masking of sunlight to such a degree that massive crop failures occurred and the year was dubbed 'the year without a summer'. More recently the eruption of Pinatubo was blamed for severe cold winters in 1992 and 1993. The eruption occurred at a time when we humans are very concerned with our impact on Earth's climate and are trying to predict its future course. Clearly we must learn to account for the effect of volcanoes if we wish to understand the natural controls of climate in addition to the anthropogenic.

Geologists also study volcanoes for their geothermal energy. People in many areas of the world e.g, Italy, Iceland, New Zealand, California USA, exploit the heat from geothermal areas to generate electricity. Here again the exploration for these systems requires understanding of the geology of volcanic systems.