Soils from Volcanoes
Why do people live on dangerous volcanoes? The main reason is the rich volcanic soil. People are willing to take high-risk gambles for the most basic things of life -- especially food. Close to an erupting volcano the short-term destruction by pyroclastic flows, heavy falls of ash, and lava flows can be complete, the extent of the damage depending upon the eruption magnitude. Crops, forests, orchards, and animals grazing or browsing on the volcano's slopes or surrounding lowland can be leveled or buried. But that is the short-term effect. In the long run, volcanic deposits can develop into some of the richest agricultural lands on earth.
One example of the effect of volcanoes on agricultural lands is in Italy. Except for the volcanic region around Naples, farming in southern Italy is exceedingly difficult because limestone forms the basement rock and the soil is generally quite poor. But the region around Naples, which includes Mount Vesuvius, is very rich mainly because of two large eruptions 35,000 and 12,000 years ago that left the region blanketed with very thick deposits of tephra which has since weathered to rich soils. Part of this area includes Mount Vesuvius. The region has been intensively cultivated since before the birth of Christ. The land is planted with vines, vegetables, or flowers. Every square foot of this rich soil is used. For example, even a small vineyard will have, in addition to grapes and spring beans on the trellises, fava beans, cauliflower, and onions between the trellis rows, and the vineyard margin rimmed with orange and lemon trees, herbs, and flowers. It also is a huge tomato growing region.
The verdant splendor and fertility of many farmlands of the North Island of New Zealand are on volcanic soils of different ages. Volcanic loams have developed on older (4,000 and 40,000 years old) volcanic ash deposits of the Waikato and Bay of Plenty regions. Combined with ample rainfall, warm summers, and mild winters, these regions produce abundant crops, including the kiwifruit found around the world in modern recipes. The altered volcanic ashes are well-drained, yet hold water for plants, and are easily tilled. Deep volcanic loams are particularly good for pasture growth (there is a large New Zealand dairy industry), horticulture, and maize.
Life-forms on the Earth's surface exist primarily by consent of nature's partnership -- the heat from the sun, and nutrients from rocks that have been decomposed and recombined into soluble molecules by chemical reactions with moisture and gases such as carbon dioxide from the atmosphere. The process is known as "chemical weathering." Chemical interactions of the atmosphere with rock release key elements from rock-forming minerals which are then accessible to plants. Volcanic rocks make some of the best soils on earth because they not only have a wide variety of common rock elements but are chemically separated into elemental components.
After the Mount St. Helens eruption in 1980, people who were living downwind from the eruption were concerned that the ash that fell would be detrimental to the agricultural farmlands of eastern Washington. This concern was countered by a group of knowledgeable earth scientists. Volcanic ash can be considered as a time-release capsule, rich in nutrients.
Link to article:
Fisher, R.V., Heiken, G., and Hulen, J.B., 1997, Volcanoes; Crucibles of Change. Princeton, Princeton University Press.Molloy, L., 1993. Soils in the New Zealand Landscape-The Living Mantle. New Zealand Society of Soil Science, Canterbury.
Sheets, P. D. and Grayson, D. K. (editors), 1979. Volcanic Activity and Human Ecology. New York, Academic Press. Copyright (C) 1997, by Richard V. Fisher. All rights reserved.