Some scientists believe that without volcanoes life as we know it would not exist on our planet. Most life on Earth ultimately depends on photosynthesis, the process in which plants use light energy to turn water and carbon dioxide into sugars. Much of the carbon dioxide in our atmosphere is continually being recycled by living things. But as rocks weather on the surface of the Earth they take up carbon dioxide from the atmosphere. This carbon dioxide is incorporated in the rock sediments that are washed down to the sea and eventually end up on the bottom of the ocean.
If that was the end of the story, the world would eventually run out of carbon dioxide, and life as we know if would splutter to a halt. Fortunately, because the seabed is continually being forced into subduction zones, much of the carbon dioxide is ultimately returned to the atmosphere by volcanic eruptions.
Volcanoes Fertilise, Cure and Energise
Carbon dioxide isnt the only thing that volcanoes recycle. Because volcanic ash is rich in many elements required by plants, it is one of natures most potent sources of fertility. Volcanic ash contains mineral fragments. When the fragments break down, the elements in them seep into the soil and fertilise it.
All around the world people have settled near volcanoes because of the fertile soils surrounding them. The market gardens in Auckland around Pukaki crater grow in soil enriched by an eruption between 20,000 and 30,000 years ago. In Italy, the land around Mt Vesuvius has been enriched by ash deposits for thousands of years and, throughout that time, has been valued for the grapes it produces for the local wine harvests.
Volcanic areas are often associated with hot springs, formed when groundwater comes into contact with hot rock below. The hot water is enriched with chemicals leached out of the rock. The peculiar chemistry of hot spring waters has often been credited with healing properties.
Until the middle of the twentieth century, people took cures for skin problems and arthritis in the warm mud and pools at Rotorua. Though the cure later fell out of fashion, its now undergoing something of a medical revival.
Volcanoes can also give us energy. Beneath the Earths surface in volcanic areas, water at 100° to 300°C can be trapped under high pressures. When accessed by drill holes, the water instantaneously turns to steam that can be used to drive turbines or heat exchanges. The geothermal power plants at Wairakei produce 220 megawatts of electricity this way.