Geology Reference
In-Depth Information
1
Introduction
This chapter outlines the periglacial concept and the historical growth of periglacial
geomorphology, and its interaction with geocryology, geomorphology, and Quaternary
science. The core of periglacial geomorphology concerns the study of freezing proc-
esses, the associated ground ice, and related landforms. Permafrost occupies a central,
but not defi ning, position. Periglacial geomorphology is a component of cold-region
geomorphology and incorporates a mix of glacial, periglacial, and azonal processes
that assume distinct characteristics in the cold non-glacial regions of the world.
Approximately one quarter of the earth's land surface currently experiences per-
iglacial conditions. During the Pleistocene an additional one fi fth was affected to
greater or lesser extent.
1.1. THE PERIGLACIAL CONCEPT
The term “periglacial” was fi rst used by the Polish geologist Walery von Lozinski in the
context of the mechanical disintegration of sandstones in the Gorgany Range of the south-
ern Carpathian Mountains, now part of central Romania (Lozinski, 1909, 1912). Sub-
sequently, at the XI Geological Congress in Stockholm in 1910, he introduced the concept
of a “periglacial zone” to describe the climatic and geomorphic conditions of areas periph-
eral to the Pleistocene ice sheets and glaciers. Theoretically, this was a tundra zone that
extended as far south as the treeline. In the mountains, it was a zone between timberline
and snowline (Figure 1.1).
Almost certainly, Lozinski was infl uenced by the Swedish geologist J. G. Andersson,
who, a few years earlier (1906, pp. 94-97), had summarized his observations on mass-
wasting on Bear Island (latitude 74° N), a cold, wet, and windswept island in the North
Atlantic. It was Andersson who introduced the term “solifl uction” to the scientifi c litera-
ture. He also described the “stone runs,” or quartzite blockfi elds, that characterize the
valley-side slopes of the equally cold and damp Falkland Islands, located in the South
Atlantic (Andersson, 1906, pp. 97-101). On hearsay alone, these phenomena had already
been compared to the “rubble-drift” and “head” deposits of southern England by James
Geikie (1894, pp. 722-723), who attributed the latter to a cold climate “more severe than
the present.”
Lozinski referred to his rock-rubble accumulations as
periglacial facies
. He observed
that similar deposits occurred on many of the upland massifs of central Europe. In sub-
sequent years, coarse angular rock-rubble accumulations on upland slopes and summits
were widely reported in the scientifi c literature. Today, they are usually referred to as
blockstreams, blockfi elds, felsenmeer, or kurums.
Two criteria are regarded as diagnostic of periglacial environments. First, there is
ground freezing and thawing. According to J. Tricart, “the periglacial morphogenetic
