Secrets of the Snow: Visual Clues to Avalanche and Ski Conditions

Introduction

Introduction This book is about snow in the mountains. Whenever snow lies on steep slopes, it may become unstable and slide away as an avalanche. Hence there will be frequent references to snow stability and clues to interpreting it. But this book is not about avalanches per se; texts dealing specifically with avalanches are listed in the bibliography. This book is intended for the interested layperson, for ski tourers, for avalanche workers, and for alpine snow country dwellers everywhere . The experienced ski or avalanche professional will find much here that is familiar (and perhaps a few things that are not). For these people, the photographs may help focus attention on aspects of snow that have become an unconscious part of their snow skills, and this introduction to “snow secrets” may help form a sound basis for developing those same skills. For all readers of whatever interest, the important theme here is to develop the ability of paying attention to the many visual clues to snow behavior. The snow surface is a sensitive register of the forces that mold it, exhibiting a constantly changing picture whose details bear a large body of information about snow stability and behavior. The molding forces are the flow of thermal and mechanical energy at the earth’s surface and the stress of gravity. These forces leave their footprints in the form of clues to snow behavior and stability for those who are alert to looking for them and have the understanding to interpret them. The primary clues are visual, but the kinesthetic sense plays an important role, and even auditory signals offer systematic evidence. This book summarizes many of the visual clues. Although the other sensory signals are important, communi3 cating their description for the most part lies beyond the capacity of the printed page. The snow surface is so variable and ephemeral that it would be a tough job indeed to cover all the potential forms in a discussion such as this. Many major and typical features presented here are illustrated by the available photos, collected by the author during a half century of watching what snow is and does. This text, however, serves a purpose beyond exhibiting basic characteristics. It will emphasize looking at the snow with attentive eyes and mind and illustrate how visual perceptions, interpreted in the light of meteorology and snow physics, lead to deductions about snow trafficability, ski conditions, and avalanche formation. This look at snow characteristics will begin with the general, largescale features of snow on the landscape, then will proceed to details of snow shapes and textures seen on a smaller, more intimate scale. The general features are largely those of form, which often can be seen at a single glance taking in snow distribution across a landscape. The details of shape and texture, on the other hand, require selective perception of, and closer attention to, separate elements in the visual field. Both are essential for gaining insight into what a given body of snow is like and what it is apt to do next. 4 Introduction ...