Frost Problems and Photo Interpretation
of Patterned Ground”?
RAGNAR THOREN,
Captain, Royal Swedish Navy
ABSTRACT: Frost conditions of both the seasonal and permanent type are of con-
siderable importance in agriculture, road building, and building construction
in Arctic areas. Photographic interpretation offers great possibilities in the
analysis of frost conditions. This is because the various types of frost condi-
tions may be identified by a number of tone and texture patterns which they
create on the ground, ad which are readily visible in aerial photography.
(Jahreszeitliche sowie fortwaehrende Frostzustaende ueben betraechtlichen
Einfluss aus in der Landwirtschaft, Strassenbau und Bau-Konstruktion in
arktischen Gebieten. Luftbild Interpretation ist von groesstem Wert in der
Analyse der Frostzustaende. Das ist der Fall, da verschiedene Arten von Frost-
zustaenden identifiziert werden koennen durch die Zahl der Schattierungen und
Gewebemuster, die dieselben auf der Oberflaeche verursachen, und die leicht zu
erkennen sind in Luftbildaufnahmen.)
NEN the water in the ground freezes,
ground frost forms. If frozen a part of
the year only, this frozen condition may be
called seasonal frost. Perennial frozen ground,
on the other hand, is called permafrost. The
thin surface layer of permanently frozen
ground, that thaws in summer and freezes in
winter, is called the active layer.
SEASONAL FROST PROBLEMS
Seasonal frost is a normal condition of the
ground in northern countries during winter-
time. For agriculture it is even of special im-
portance, and actually favorable for the win-
tering of rye, while snowfall on nonfrozen
cround is dangerous for such wintering.
For roads, on the other hand, severe ground
frost may end with a catastrophe. The process
of water freezing in soils will often be accom-
panied by expansion resulting in lifting the
ground; this is called frost-heaving. Heaving
of the ground surface caused solely by the
crystallization of the original water contents
in the freezing soil, independent of any water
supply, is always very slight and usually of
no practical importance. All frost-heaving of
any practical significance depends upon the
water suction to the freezing layers, mainly
from a ground water supply. This suction is of
capillary nature and varies with the mechan-
ical composition of the soil. Frost-heavings of
about 8 inches (20 cm.) are quite common in
Scandinavia, especially in the northern parts.
'The silt and loam sediments show a normal
heave of about 6-8 in. (15-20 cm.), and at
places where frost-boil appears during thaw-
ing (see below), the heave can be 12-16 in.
(30—40 cm.) or more. Moraine-ground usually
shows a less amount of heave, about half of
that for silt; 8 inches, however, is not unusual
(Beskow).
Frozen soil often shows a special structure
with layers or lenses of pure ice within the
soil; this is called ice-stratified soil. These ice
layers may show very different structural pic-
tures, depending on the type of soil. In gen-
eral the ice layers are parallel to the ground
surface, i.e. mostly horizontal. The finer the
soil, the coarser the structural elements.
When the ice in the ground melts there will
be an excess of water, thereby lowering the
supporting capacity of the roads. If traffic
then is allowed, the road surface will most
likely break down. The melting process may
be accompanied by a soil-heaving phenome-
na, called frost-boil. Among the processes of
soil freezing and thawing, frost-boil is the
most damaging one to the highways.
* This paper is a part of the 1960 program of Commission VII (Photographic Interpretation), of
the International Society of Photogrammetry, and is submitted by the Commission’s Working Group 3,
“Surface Configuration, drainage, soils and geology.”
+ See also the other report of this Working Group 3 which is in this issue and also the Group Report
in PHOTOGRAMMETRIC ENGINEERING, Vol. XXV, (1) 121.
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