Geology Reference
In-Depth Information
10
Azonal Processes
and Landforms
Fluvial processes assist in fashioning the periglacial landscape. Both large and small
rivers exist, all dominated to varying extent by spring snowmelt-induced (nival) peak
discharge. Freeze-up and break-up are distinct cold-climate characteristics, together
with fl uvio-thermal erosion. Although all types of stream channel morphology can be
found in periglacial environments, braided channels are most common. The asymme-
try of many small valleys refl ects a complex interaction between slope and channel
processes.
Wind action is enhanced by the lack of vegetation, and by the ability of wind not
only to transport and redistribute snow but also to use snow as an abrading agent.
Niveo-eolian deposits illustrate the intimate connection between wind and snow. Wind
also infl uences, via the snow cover and direct evaporation, microclimates and ground-
thermal regimes. Wind also infl uences ice movement and wave action in both marine
and lake environments.
Beach processes are restricted by the presence of sea ice and beach-fast ice for parts
of the year. Coastlines formed in ice-rich permafrost sediments are subject to thermo-
abrasion and rapid modifi cation.
10.1. INTRODUCTION
Many azonal processes are either enhanced or inhibited by cold-climate conditions while
others assume special characteristics. This is the case for fl uvial, eolian, and coastal proc-
esses and justifi es their collective treatment in this chapter. The intent is not to present a
systematic treatment of each since other geomorphology texts are readily available.
Instead, the approach highlights those aspects that are peculiar to, and achieve their great-
est importance in, periglacial environments.
10.2. FLUVIAL PROCESSES AND LANDFORMS
The large-scale organization of periglacial terrain is not unlike that of other environments.
A well-developed drainage network exists, even in those areas that have recently emerged
from beneath Quaternary ice sheets and glaciers. It is most striking in the extreme high
latitudes, where, in spite of aridity, and in the absence of vegetation, the intricacies of the
network are clearly visible (see Figure 2.4). In broad terms, the fl uvial network is com-
posed of two types of rivers. First, large rivers, such as the Mackenzie and Yukon rivers
