XI

PREFACE

Volcanic eruptions are awesome and destructive; however, this natural phe- nomenon is beneficial in the long term. One of the earliest known written records of a natural disaster concerned the eruption of Pompeii in A.D. 79, and was recorded by Pliny the Younger in his letters to the historian Tacitus (Jashemski, 1979). Volcanic eruptions, ranging in intensity and numbering between 17 and 27 per year during the past decade (Bullard, 1984), continue to remind us of their potential impacts on the environment. Violent volcanic eruptions range from complete obliteration of the landscape near the volcano, to a mere dusting of tephra at great distances. The most obvious effect is the destruction caused by catastrophic ejection of ash, lava, pyroclastic flows and/or mudflows. These agents of destruction may result in loss of wildlife, vegetation, and even human lives.

There is a tendency to view volcanoes primarily as agents of destruction and to overlook their beneficial contributions. The beneficial effects of volcanic eruptions are often more subtle; occurring on a geologic time-scale rather than during the lifetime of an individual. They include building of continents, oceanic islands, and the ocean floor; creation of magnificent scenery and recreation areas; and the development and rejuvenation of soils which provide an environment favorable to the eventual establishment of lush vegetation and the ecology of organisms, including human beings. The periodic additions of volcanic ash renew the long- term fertility status by providing a source of nutrients from the rapid weathering of ash.

Soils formed in volcanic ash have many distinctive properties that are rarely found in soils derived from other parent materials. It is estimated that soils derived from volcanic ejecta are distributed over approximately 0.8% of the earth’s surface (Leamy, 1984). These soils have a high potential for agricultural production as illustrated by the fact that many of the most productive regions of the world are located near active or dormant volcanoes and the most densely populated areas in regions, such as Indonesia, are found near volcanoes. To maximize the productivity of volcanic ash soils and to minimize the deterioration of these soils, proper management, based on an understanding of the unique physical, chemical, and mineralogical properties of these soils, must be practiced.

Volcanic ash soils did not receive worldwide recognition among soil scientists until the middle of this century; however, a considerable understanding of the genesis, unique properties, and productivity of these soils was established in Japan

XI1 PREFACE

and New Zealand several decades earlier. It was only in 1960 that volcanic ash soils were recognized as a distinct category of soils with unique properties in the international system of soil classification proposed by the Soil Survey Staff, Soil Conservation Service, United Sates Department of Agriculture. This recognition stemmed from an urgency to determine the potential agricultural productivity of the world’s soils, necessitated by the increased demand for food production to feed the rapidly increasing world population.

It is interesting to note that the discovery, characterization, and significance of short-range-order minerals and noncrystalline colloidal materials, such as imogo- lite, allophane, laminar opaline silica, ferrihydrite, and Al/Fe humus complexes, owe their recognition to the intensive studies of volcanic ash soils associated with efforts to classify these soils. These achievements have greatly contributed to the establishment of the concept and science of variable charge soils.

A renewal and upsurge of interest in volcanic ash soils was initiated by the proposal for an “Andisol” soil order in Soil Taxonomy, first proposed by Guy Smith in 1978. Development, testing and refinement of criteria to define the Andisol soil order brought together, for the first time, many of the prominent soil scientists working on volcanic ash soils. After 12 years of study, the Andisol soil order was finally adopted as the 11th soil order in Soil Taxonomy (Soil Survey Staff, 1990). During these 12 years, a wealth of ideas and knowledge was exchanged and debated.

The purpose of this book is to synthesize and integrate our current under- standing of volcanic ash soils including the topics of morphological and physical characteristics, chemical and mineralogical properties, soil genesis and classi- fication, and productivity and utilization of these soils. The information and experience on volcanic ash soils shared by the authors are mostly limited to soils formed in the middle latitudes or temperate regions. Thus, this book is written largely from this perspective. The authors realize, however, that in order to present a more balanced and complete international understanding, the related literature on volcanic ash soils of the tropical regions should be addressed. More than half of the volcanic ash soils of the world are located in the tropics where climatic conditions, such as temperature and precipitation, are significantly different from those of the temperate regions. Since climate greatly affects soil forming processes, the soils formed in tropical regions are expected to differ considerably from those formed in the temperate regions. Unfortunately, the limited literature on tropical volcanic ash soils available to the authors makes it impractical to rigorously discuss this group of soils in the present monograph.

September, 1992 SADAO SHOJI, MASAMI NANZYO

and RANDY DAHLGREN

PREFACE XI11

REFERENCES

Bullard, EM., 1984. Volcanoes of the Earth, 2nd revised edition. University of Texas Press, Austin, Texas.

Jashemski, W.E, 1979. Pompei and Mount Vesuvius A.D. 79. In: P.D. Sheets and D.K. Grayson (Editors), Volcanic Activity and Human Ecology. Academic Press, New York, London, Toronto, Sydney and San Francisco, pp. 587-622.

Leamy, M.L., 1984. Andisols of the world. In: Congresco international de Suelos Volcanicos. Commu- nicaciones. Universida de La Laguna Secretariado de Publicaciones, serie informes 13, pp. 368- 387.

Soil Survey Staff, 1990. Keys to Soil Taxonomy, 4th edition. AID, USDA-SMSS Technical Monograph No. 19. Blacksburg, Virginia.