The earth needs to blow off some steam

Volcanoes aren't just for show – it turns out we need them

If you don't like active volcanoes, go to Mars. But be prepared to become your own life support system.

As the authors of this interesting little book put it: "Volcanism is the surface manifestation of a living Earth." Volcanoes are relief valves for the high-pressure system that recycles large chunks of the outer crust through the planet's molten interior and returns life-sustaining materials to the surface.

Volcanoes have supplied much of our water. Their ash falls have enriched soils. Their gases have helped form our atmosphere. If Mars' recycling system hadn't shut down eons ago, life might thrive there today.

Humans have a precarious cost-benefit relationship with this essential phenomenon. We can catch a lot of grief when volcanoes explode or ooze all-consuming lavas.

Geoscience now mediates that relationship as our growing understanding of volcanic mechanisms helps us better manage the risks. This makes volcano science a humanistic enterprise.

That's the authors' main point in "Volcanoes in Human History." They could have made it with more verve and poetry, but their somewhat stodgy style serves their intent not to focus merely on dramatic accounts of volcanic carnage.

The authors – Jelle de Boer, a volcanologist, and Donald Sanders, a geologically informed science writer – have a larger perspective. They show how political, economic, and environmental consequences of that carnage can reverberate for centuries.

For instance, there's well established, although not definitive, evidence that a major Bronze Age eruption changed the course of Mediterranean history over 3,500 years ago. It happened at Thera, one of the Santorini Islands some 70 miles north of Crete.

Immediate environmental effects – tsunamis, ash falls, and possibly atmospheric shock waves – devastated Crete's powerful Minoan civilization. Mycenaean Greeks took over and extended their influence throughout the eastern Mediterranean.

The authors have little to add to this well known tale. But their insight lies in connecting the volcanic system responsible for the event to the on-going history of that region.

Other lesser volcanic effects have occurred since the Bronze Age to challenge inhabitants to learn to live safely.

Mt. Vesuvius's burial of Roman Pompeii and Herculaneum is another familiar event that helps make the authors' point. The well-preserved remains show how swiftly disaster overtook those two towns. Their inhabitants did not know that seemingly harmless precursor eruptions could suddenly turn nasty.

They knew nothing of pyroclastic flows of burning gases and suffocating ash that overtake fleeing humans with express-train speed.

They did not know that rapid buildup of ash would soon collapse roofs under which they innocently took shelter. Had they known, they might have hastened timely evacuations.

Today, we do know about these and many other aspects to volcanic behavior.

Given its long record of major and minor eruptions, Vesuvius has become the most intensely studied volcano on the entire planet.

Volcanologists have no doubt that it will erupt violently again. They just can't say when. While they search for predictive clues, authorities in nearby Naples try to make the most of present knowledge to plan for what one day may be the greatest evacuation in human history.

In all, the authors present 11 volcanoes to explain what it means to live with volcanic hazards. It's easy to look back and say fewer people would have chosen to live in such risky places if they had know what was involved. But that's cold comfort. Our crowded planet now offers many at-risk populations little alternative – as in the case of Naples.

We have to make the most of our scientific understanding to deal with hazards that people cannot avoid. We should love our life-sustaining planet, risks and all, for we certainly can't leave it. This book will help interested readers understand some of its foibles.

• Robert C. Cowen writes about science for the Monitor.

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