Corps de l’article
In their Introduction, the authors provide a convincing justification for creating this unique review of the geomorphology and sedimentology of colluvium. Colluvium is a very common sedimentological unit on the surface of the earth, as widespread as any sloping ground both on the surfaces of the continents and under the sea. It is also a unit that is very important to human interests, because it is one of the most dynamic surficial units, hosting a range of potent geomorphological processes that place serious constraints on land use. Yet, precisely because of its dynamic, transient nature, colluvium is poorly represented in conventional sedimentology texts. The reason is simply because it is largely absent from the bulk of aged deposits formed in large sedimentary basins (rhythmites and mélanges being the only notable exceptions). It is a unit that is constantly in motion, that forms a changing, transient, but important segment of the sediment cascade.
Because it is intended to fill in an obvious gap in the literature, the book is structured on the model of classical facies catalogues such as, for example, Walker (1992). After a brief review of sedimentological terminology and rheological theories, the individual processes of slope formation are systematically described in individual sections of Chapter 2. These include rock fall, rock avalanches, snow avalanches and slush flows, creep and solifluction, slides, debris flows, dry granular flows, surficial water erosion and wind erosion. This reviewer would prefer to see a separate treatment of debris avalanches (shallow, open-slope variety of debris flows) and associated colluvial aprons. A separate section on gully erosion would also be useful.
The much shorter Chapter 3 reviews the structure and evolution of talus cones and fluvial and debris fans. A very brief review of the role of slope deposits in applied geology and an extensive bibliography complete the book. Each section is amply illustrated by diagrams and black-and-white photographs, concentrating on sedimentological features of the various types of deposits.
It would be difficult to criticize a volume that successfully covers such an obvious opening in sedimentological and geomorphological literature. Nor does this volume need to be criticized, as the coverage of the subject is authoritative and systematic. This reviewer finds only that the engineering geology literature, which has long been the leading resource of ideas and data related to the phenomenology of slope processes, could perhaps have been more thoroughly exploited. For example, engineers have recently made fair progress in dynamic modeling of the motion of rock falls as well as various types of flow-like landslides, which may warrant more thorough description. Of course, at a little over 250 pages, the present volume cannot be considered as the ultimate, exhaustive review of the important subject of the geology of slope processes. It is, nevertheless, an excellent start and a very useful reference for any geoscientist.
- Walker, R.G., 1992. Facies models. 2nd ed. Geoscience Canada, Reprint Series, 1: 1-10.