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GEOL 495 1998
Columbia Plateau/Channeled Scablands Field Course
Chapter 5. Volcanic ash-physical, edaphic, and chronologic significance
in the pacific northwest

Introduction

Disastrous effects of volcanism are obvious to those unfortunates too near an event in time and space. Distance in both dimensions however, provides advantages for agricultural pursuits. Northern Idaho and much of the pacific northwest are blanketed by a thin veneer of ash due to Holocene volcanism that significantly enhances soil productivity compared to local soils developed in parent materials lacking ash. Benefits of ash are also realized in engineering applications, some far older than most people recognize. The focus of this paper is on the physical, chemical, and mineralogic properties of ash that are responsible for the unique behavior of this material in agriculture and engineering. The excellent basis for ash as a time-stratigraphic marker, and a few caveats, will also be discussed.

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