Permafrost as a Natural Phenomenon
EA-I. (Robert F. Black)
PERMAFROST AS A NATURAL PHENOMENON
CONTENTS
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Page
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Introduction
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1
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Constitution and Properties of Permafrost
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2
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Extent
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2
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Thickness
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3
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Temperature
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4
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Character
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5
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Relation to Terrain Features
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6
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Origin
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7
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Geologic Ramifications
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8
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Engineering Significance
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12
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Biologic Significance
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13
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Factors Affecting Permafrost
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14
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Practical Applications
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17
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Recognition and Prediction
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19
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Construction
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20
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Water Supply
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22
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Sewage Disposal
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23
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Agriculture
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24
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Mining
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24
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Refrigeration and Storage
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26
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Trafficability
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26
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Military
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27
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Future Research Needed
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28
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Bibliography
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30
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EA-I. Black: Permafrost as a Natural Phenomenon
LIST OF FIGURES
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Page
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Fig. 1
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Areal distribution of permafrost in the
Northern Hemisphere
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2-a
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Fig. 2
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Representative cross section of permafrost areas
in Alaska and Asia
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4-a
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Fig. 3
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Representative temperature profiles in areas of
continuous, discontinuous and sporadic permafrost
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4-b
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EA-I. (Robert F. Black)
PERMAFROST AS A NATURAL PHENOMENON
INTRODUCTION
Permafrost (perennially frozen ground) is a widespread geologic
phenomenon whose importance and ramif
ac
^
ica^
tions are rapidly becoming better
^
✓^
known and more clearly understood. For many decades European scientists
have been describing surficial features produced by frost action and
permafrost, but for the most part they have given only passing reference
to perennially frozen ground. The current problem is to understand perma–
frost so as to be able to evaluate it in the light of any particular endeavor,
whether practical or academic. To understand permafrost we need a precise
standardized terminology, a comprehensive classification of forms, a
systemization of available data, and coordination of effort by geologists,
engineers, physicists, botanists, climatologists, and other scientists in
broad research programs. These objectives are only gradually being realized.
This article is largely a compilation of or reference to recent available
literature. Its purpose is to acquaint geologists, engineers, and other
scientists with some of the many ramifications and practical applications
of permafrost. New data from unpublished manuscripts of the U.S. Geological
Survey are included where appropriate for clarity or completeness. References
in this paper generally are only to the later American or German works, as
EA-I. Black: Permafrost as a Natural Phenomenon
most contain accounts of the earlier literature. Unfortunately, the bulk
of the literature is in Russian and unavailable to the average reader;
some of it has been summarized by Muller (41). A list of 190 Russian articles
that deal with permafrost is given by Weinberg (97). The Arctic Institute
of North America (82) is currently preparing an annotated bibliograph
^
y^
of all
^
✓^
arctic literature, including permafrost.
The multitude of problems associated with frost action appropriately
should accompany any discussion of permafrost. However, lack of space permits
only passing reference to the relationship between permafrost and frost action.
An annotated bibliography on frost action has been prepared by the Highway
Research Board (43).
CONSTITUTION AND PROPERTIES OF PERMAFROST
The term permafrost was proposed and defined by Muller (41). A longer,
but more correct phrase, is “perennially frozen ground” (77). The difficulties
of the present terminology have been discussed by Bryan (4; 6) who proposed a
new set of terms. These are discussed by representative geologists and engineers
(7). Such terms as cryopedology, congeliturbation, congelifratcion, and
cryoplanation have been accepted by some geologists (9; 17; 35; 85) in order
to attempt standardization of the terms referring to perennially frozen ground
and frost action. The term permafrost has been widely adopted by agencies of
the United States Government, by private organizations, and by scientists and
laymen alike. Its use is continued in this article as it is simple, euphonious,
and easily understood by all.
Extent
. Much of northern Asia and northern North America contains perennially
^
Fig. 1^
frozen ground (Fig. 1) (14; 41; 46; 72; 77; 84).
Figure 1
EA-I. Black: Permafrost as a Natural Phenomenon
The areal subdivision of permafrost into continuous, discontinuous, and
sporadic zones is already possible on a small scale for much of Asia but, as
yet, only for part of North America. Refinements in delineation of these
zones are being made each year. The southern margin of permafrost is known
only approximately, and additional isolated bodies are being discovered as
more detailed work is undertaken. The southern margin of permafrost has
receded northward within the last century (47).
Permafrost is absent or thin under some of the existing glaciers, and
it may be absent in areas recently exhumed from ice-cover. A greater extent
of permafrost in the recent geologic past is inferred from phenomena associated
with permafrost (9; 30; 53; 54; 58; 60; 66; 83; 84; 98; 106). Some of the
more important phenomena are fossil ground-ice wedges, solifluction deposits,
block fields and related features, involutions in unconsolidated sediments,
stone rings, stone stripes and related features, and asymmetric valleys (66).
The presence of permafrost in earlier geologic periods can be inferred from
the known facts of former periods of glaciation and from fossil periglacial
forms.
In the Southern Hemisphere, permafrost is extensive in Antarctica. It
probably occurs logically in some of the higher mountains elsewhere, but its
actual extent is unknown.
Thickness
. Permafrost attains its greatest known thickness of about
2,000 feet (620 meters) at Nordvik in northern Siberia (I. V. Poir
e
^
é^
, oral
^
accout ✓^
communication). Werenskiold (99) reports a thickness of 1,050 feet
^
(^
320 meters
^
)^
^
✓^
in the Sveagru
n
van coal mine in Lowe Sound, Spit
z
^
s^
bergen. In Alaska its
^
✓^
^
✓^
greatest known thickness is about 1,000 feet, south of Barrow.
EA-I. Black: Permafrost as a Natural Phenomenon
Generally, the permafrost thins abruptly to the north under the Arctic
Sea. It is discontinuous and sporadic as it gradually thins to the south
^
Fig. 2^
(Fig. 2) (14; 41; 77).
In areas of comparable climatic conditions today, permafrost is much
thinner in glaciated areas than in nonglaciated areas (77; 78).
Unfrozen zones within perennially frozen ground are common near the
surface (41) and are reported to occur at depth (14; 77). They have been
interpreted as indicators of climatic fluctuations (14; 41), or as permeable
water-bearing horizons (77).
Temperature
. Below the depth of seasonal change, the temperature of
perennially frozen ground ranges from slightly less than 0°C. to about −12°C.
(I. V. Poir
e
^
é^
, oral communication). In Alaska the minimum temperature recorded
^
accout ✓^
to date is −9.6°C. at a depth of 100-200 feet in a well about 40 miles south–
west of Barrow (J. H. Swartz, 1948, written communication). Representative
temperature profiles in areas of continuous permafrost are shown in Figure 3A;
in areas of discontinuous permafrost, in Figure 3B; and in areas of sporadic
^
Fig. 3^
permafrost, in Figure 3C.
Temperature gradients from the base of permafrost up to the depth of
minimum temperature vary from place to place and from time to time. In
1947-48, four wells in northern Alaska had gradients between 120 and 215 feet
per degree centigrade (data of J. H. Swartz, G. R. MacCarthy, and R. F. Black).
The shape of a temperature curve indicates pergelation or depergelation–
aggradation or degradation of permafrost (41; 77). Some deep temperature
profiles have been considered by Russian workers to reflect climatic fluctua–
tions in the recent geologic past. No known comprehensive mathematical
approach has been attempted to interpret past climates from these profiles,
Figure 2
[]
Figure 3
EA-I. Black: Permafrost as a Natural Phenomenon
although it seems feasible. Some of the effects of Pleistocene climatic
variations upon geothermal gradients have been discussed by Birch (2) and
Ingersoll and Zobell (32).
Character
. Permafrost is defined on the basis of temperature, and it
may encompass any type of natural or artificial material, whether organic or
inorganic. Generally, permafrost consists of variable thicknesses of
perennially frozen surficial, unconsolidated materials; bedrock; and ice.
Physical, chemical, or organic composition, degree of induration, texture,
structure, water conte
c
^
n^
t, etc., very widely and are limited only by the
^
✓^
extremes of nature o
f
^
r^
the caprice of mankind. For example, perennially
^
✓^
frozen mammals, bacteria, artifacts, beds of sand and silt, lenses of ice, and
beds of peat can collectively be lumped under the term permafrost. Ground
perennially below freezing but containing no ice has been called “dry per–
mafrost” (41).
Permafrost composed largely of ice is abundant, particularly in poorly
drained, fine-grained materials. The ice occurs as thin films, grains,
fillings, veinlets, large horizontal sheets, large vertical wedge-shaped
masses, and irregular masses of all sizes. Many masses of clear ice are
arranged in geometric patterns near the surface, i.e., polygonal ground and
honeycomb structure. The ice may be clear, colorless, yellow, or brown. In
many places it contains numerous oriented or unoriented air bubbles, silt,
clay, or organic materials. Size, shape, and orientation of the ice
crystals differ widely. Discordant structures in sediments around large
masses of ice are evidence of growth (38; 77; 78).
EA-I. Black: Permafrost as a Natural Phenomenon
Relation to Terrain Features
. In the continuous zone of permafrost, the
upper limit (permafrost table, 41) is generally within a few inches to 2 feet
of the surface. Large lakes and a few large rivers lie in thawed areas
slightly larger than the basins they occupy (3; 41). Well-drained, coarse–
grained materials may thaw annually to a depth of 6 feet. Poorly drained,
fine-grained materials protected from solar radiation and insulated with
m
i
^
o^
ss and other vegetation may thaw annually to a depth of only 4 inches.
^
✓^
In the discontinuous zone permafrost is absent under most major rivers
and lakes. Permafrost may be absent in the tops of some well-drained low
hills. Seasonal thaw (active layer, 41) penetrates 1 to 10 feet depending
upon insulation, amount of energy absorbed from solar radiation, drainage,
and type of material.
Sporadic bodies of permafrost may be relics below the active layer or
may be forming in favorable situations in poorly drained, fine-grained
materials on north-facing slopes. In the zone of sporadic permafrost, the
active layer may or may not reach the permafrost table, and ranges between
2 and 14 feet in thickness.
Generally, the depth of thaw is at a minimum in northern latitudes and
increases to the south. It is at a minimum in peat or highly organic sediments
and increase successively in clay, silt, and sand to a maximum in gravelly
ground or exposed bedrock. It is less at high altitudes than at low
altitudes and less in poorly drained ground than in dry, well-drained ground.
It is at a minimum under certain types of tundra and increases successively
under areas of bog shrubs, black spruce, larch, white spruce, birch, aspen,
and poplar to a maximum under tall pines. It is less in areas of heavy
snowfall, in regions having cloudy summers, and on north-facing slopes
(41; 77; 78; 84).
EA-I. Black: Permafrost as a Natural Phenomenon
Works of man commonly upset the natural thermal equilibrium and may tend
to destroy permafrost or to aid in its formation. Most roads, runways, and
other structures on the surface of or in the ground generally have
s
lower
^
[: S] ✓^
permafrost tables than undisturbed natural areas adjacent to them. Structures
above the ground and insulated from the ground partially protect the surface
from solar radiation and commonly produce higher permafrost tables.
Origin
. The origin of perennially frozen ground is discussed by Muller (41),
Zeuner (106), Taber (77), Cressey (14), Nikiforoff (44), Leffingwell (38), and
others. In general, it can be stated that most sporadic bodies of permafrost
are relics of colder climates. Discontinuous bodies of permafrost are largely
relics but under favorable conditions may grow in size, and pergelation (4),
of new deposits may take place. In areas of continuous permafrost, heat is
being dissipated actively from the surface of the earth to the atmosphere, and
new deltas, bars, landslides, mine tailings, and other deposits are being per–
gelated (incorporated in the permafrost).
Local surface evidence indicates that in places heat is being absorbed
into the base of permafrost faster than it is being dissipated at the surface
(29; 104). Hence, the cold reserve is being lessened and the thickness of
permafrost is decreasing from the base upward.
The mean annual air temperature required to produce permafrost undoubtedly
varies many degrees because of local conditions. Generally, it is given as
30° to 24°F. Theoretically permafrost can form above 32°F. (80), and apparently
is doing so locally in parts of southwest Alaska that have poor drainage,
abundant vegetation, cloudy summers, and relatively slight absorption of solar
radiation (S. Abrahamson, oral communication).
EA-I. Black: Permafrost as a Natural Phenomenon
The relative effects of past climates have been inferred qualitatively
through a study of present temperature profiles, ancient deposits, pollen
analysis, changes in floras, the regimen of plants, soil structures, block
fields, etc.
The origin of large clear ice masses in the permafrost is a special
problem in itself. Numerous theories are extant and one or more may apply to
a particular mass of ice (38; 77).
GEOLOGIC RAMIFICATIONS
Throughout the Arctic and Subarctic the role of permafrost is extremely
important. As an impervious layer in zones of continuous permafrost, it
exerts a drastic influence on surface waters, completely prevents precipita–
tion from entering the natural ground-water reservoirs, and commonly causes
a concentration of organic acids and mineral salts in suprapermafrost water.
In zones of discontinuous permafrost, and less so in areas of sporadic perma–
frost, ground-water movement are interrupted or channelized. The quality
of water, too, can be materially affected by storage for centuries, and
subsequent release by thawing of organic and inorganic materials (36). In
fact, our present concepts of ground-water reservoirs, ground-and surface–
water movements, infiltration, quality of water, and so on, must be modified
in considering permafrost as a new geologic formation, generally not uniform
in composition or distribution, that transcends all rock and soil formations.
Furthermore, it must be considered as much in regard to past as to present
conditions.
In cold climates, physical disintegration (frost splitting, congeli–
fraction) plays a more important role than chemical weathering. The repeated
EA-I. Permafrost as a Natural Phenomenon
freezing of water-
w
^
s^
aturated materials and the growth of ice crystals in
^
✓^
numerous small pores, cracks, joints, cleavage planes, or partings is
by far the most effective disruptive proces
.
^
s.^
Taber (77) has shown that,
^
✓^
without water, disintegration is generally much slower. Permafrost is one
of the most important agents in keeping soils supersaturated (containing
more water than pore space; a suspension) and in keeping rock fragments wet.
Mass-wasting processes in the Arctic and subarctic are instrumental
in the transport of tremendous volumes of material. With the exception of
unbroken bedrock, the materials on the surface of slopes greater than 1° to
3° are everywhere on the move in summer. The amount of material involved
and the rapidity of such movements impress all who have studied them (96).
Permafrost, on thawing slightly in summer, supplies a lubricated
surface and additional water to materials probably already saturated. Hence,
solifluction, mud flows, and other gravity movements take place with ease
and in favorable locations even supply material to streams faster than the
streams can remove it (94). Bryan (5) has coined the term “cryoplanation”
to cover such processes (including also frost heaving normal to slopes and
settling vertically), which in the Arctic are instrumental in reducing the
landscape to long smooth slopes and gently rounded forms. Such physiographic
processes are only partly understood and their effects only quali
^
ta^
tively
^
✓^
known (5).
Permafrost, by aiding in maintaining saturated conditions in surficial
materials, indirectly aids in frost-stirring (congeliturbation), frost-splitting,
and mass-wasting processes in such a way that, in places, bedrock is disinter–
grated, reduced in size, thoroughly mixed, and rapidly transported. The result
is a silt-sized sediment that is widespread in the Arctic. Various authors
EA-I. Permafrost as a Natural Phenomenon
(5; 29; 67; 77; 87; 106) disagree as to whether some of the material is
derived from aeolian, lacustrine, or local frost-splitting and mass-wasting
processes. Size-grade distribution curves, mineral comparisons, chemical
analyses, comparisons with glacial materials and with organic materials
^
,^
etc.,
^
✓^
have been used by various investigators to prove their point, but the
differences of opinions have by no means been resolved.
Frost action (frost heaving, frost stirring, and frost splitting) and
gravity movements result in many surface forms that are found most abundantly
in areas of permafrost, i.e.,
strukturb
o
^
ö^
den
, involutions, frost boils, hummocks,
^
✓^
altiplanation terraces,
terr
e
^
a^
cettes
, and soil stripes (9; 13; 25; 28; 35; 58;
60; 63; 65; 70; 77; 83; 84; 85; 96; 106). Annual freezing in permafrost
areas also forces changes in surface- and ground-water migration and commonly
results in pingos, frost blisters, ice mounts, icings,
Aufeis
^
Aufeis
^
, and other related
^
✓^
forms (41; 42; 62; 84). Many of the forms produced by frost action and seasonal
freezing are closely related in character and origin; however, the lack of a
standardized terminology for these features produces a perplexing picture.
Little can be said quantitively regarding the importance of frost action
(and indirectly permafrost) in ancient sediments and soils (106). Throughout
the world, deposits of former glaciers have been found in the stratigraphic
sequence. Undoubtedly permafrost was present during those times of glaciations,
as fossil forms derived from frost action and permafrost are known (30; 35; 58;
60; 65; 84; 94; 105; 106). These forms provide data on the processes that
produced the surficial materials and on the environment of deposition. These
features are only now being recognized and studied in the detail that is
warranted (5).
EA-I. Black: Permafrost as a Natural Phenomenon
Permafrost throughout the world has provided a wealth of material for
paleontologists and archeologists. In perennially frozen Alaskan placers,
investigators have found more than 27 different plants (11), including whole
forests of buried stumps (26); numerous iron and other bacteria; algae;
87 species of diatoms (77); bones of at least 20 species of large mammals,
represented by tens of thousands of speciments (77; 100); and a few species
of mollusk
a
^
s^
, sponges, and insects (77). Permafrost in Siberia has been a
^
✓^
storehouse for Pleistocene mammals (81).
Permafrost upsets many readin
^
g^
s taken by geophysicists in determining
^
✓^
the internal constitution of the earth. Velocities of seismic waves, for
example, are materially increased by frozen ground containing much ice and
may result in considerable errors in determinations of depths. Although the
actual increases are not definitely known, they probably range within 1,000
to 8,000 feet per second. Unfortunately, the base of permafrost causes, with
present equipment, no satisfactory reflections or refractions, and seismic
methods cannot be used to determine the thickness or variability of the zone
distorting the seismic waves. Difficulties in drilling, preparing explosive
charges, checking ground waves, and obtaining interpretable effects are augmented
in permafrost areas.
Electrical methods, especially resistivity methods, give promise of solving
some of the difficulties in determining the extent and thickness of permafrost
(20; 34; 41; 74). Generally, resistivities of frozen silt and gravel are
several thousand ohms higher than those of comparable unfrozen materials and
may be 20 to 120 times as high (34; 74). However, as is well known, the type
of material is less important than the amount of unfrozen ground water and
dissolved salts within the material. Even in frozen ground these factors are
EA-I. Black: Permafrost as a Natural Phenomenon
so variable that resistivity data can be interpreted with reliability only
by experienced men and generally only for areas where some positive checks
can be made through drilling.
Sumgin and Petrovsky (73) discuss a new radio-wave technique, used
where permafrost is below −5°C.
ENGINEERING SIGNIFICANCE
In Alaska during World War II, difficulties encountered by the Armed
Forces in obtaining permanent water supplies, and in constructing runways,
roads, and buildings in permafrost areas focused attention on permafrost
as nothing else could (1; 33; 78; 101). O^n^ly then did most people realize ^✓^
that in Russia similar difficulties with railroads, roads, bridges, houses,
and factories had impeded colonization and development of the North for
decades. Now, with the recent progress in aviation and because of the
strategic importance of the North, active construction and settlement for
military and civilian personnel must increase, and the problems of permafrost
must be solved.
Fortunately we can draw on the vast experience of the Soviet Union.
Their engineers have shown that it is “…a losing battle to fight the forces
of frozen ground simply by using stronger materials or by resorting to more
rigid designs. On the other hand, the same experience has demonstrated that
satisfactory results can be achieved and are allowed for in the design in
such a manner that they appreciably minimize or completely neutralize and
eliminate the destructive effect of frost action… Once the frozen ground
EA-I. Black: Permafrost as a Natural Phenomenon
problems are understood and correctly evaluated, their successful solution
is for the most part, a matter of common sense wher
^
e^
by the frost forces are
^
✓^
utilized to play the hand of the engineer and not against it.” Hence, “…it
is worth noting that in Soviet Russia since about 1938 all governmental
organizations, municipalities, and cooperative societies are required to
make a thorough survey of the permafrost conditions according to a prescribed
plan before any structure may be erected in the permafrost region….”
(41, pp. 1-2, 85-86).
Specifically, permafrost must be considered in construction of buildings,
roads, bridges, runways, railroads, dams, and reservoirs; in problems of
water supply, sewage disposal, telephone lines, drainage, excavation, ground
storage, and in many other ways. Permafrost can be used as a construction
material or as a base for construction, but steps must be taken to insure its
stability, Otherwise, it must be destroyed and appropriate steps taken to
prevent its formation.
BIOLOGIC SIGNIFICANCE
Permafrost, because of its low temperature and ability to prevent
runoff, is a potent factor that aids in controlling vegetation in the Arctic
and Subarctic (40). Many places have semiarid climate, yet have luxuriant
growths of vegetation because permafrost prevents the loss of precipitation
through underground drainage (low evaporation possibly as important). Such
conditions are natural breeding environments for mosquitoes and other insects.
Conversely, luxuriant growths of vegetation, by insulating the permafrost
in summer, prevent deep thawing and augment cold soil temperatures. Hence,
those plants with deep root systems, such as certain trees, are dwarfed or
absent, and nourishment available to smaller plants is limited.
EA-I. Black: Permafrost as a Natural Phenomenon
Raup (56; 57) points out that much arctic soil is unstable because
of fro
son
^
st^
action (commonly associated with permafrost), and that standard
^
✓^
biological methods of describing plant communities do not apply. The normal
associations have been greatly disturbed, special communities for different
frost forms can be identified, and above all the plant communities must be
described on the basis of their physical habitat.
Permafrost probably controls the distribution of some animal species,
such as the frogs or toads, that require thawed ground into which they can
burrow for the winter. The fox can have dens only in dry elevated places
where the depth of thaw is 2 feet or more. Similarly, permafrost affects
worms, burrowing insects, and other animals that live in the ground.
Indirectly, permafrost, by exercising some control on types of vegetation,
i.e., tundra vs. forest, also exercises some control on the distribution of
animals such as the reindeer and porcupine.
FACTORS AFFECTING PERMAFROST
Most major factors affecting permafrost are recognized qualit
^
at^
ively, but
^
✓^
none is well known quantit
^
at^
ively. These factors are easily visualized by
^
✓^
turning to the original definition of the term permafrost. As permafrost
is fundamentally a temperature phenomenon, we may think of it as a negative
temperature produced by climate in material generally of heterogeneous
composition. Permafrost is produced because, through a combination of many
variables, more heat is removed from a portion of the earth during a period
of 2 or more years than is replaced. Hence, a cold reserve is established.
Basically, the process can be reduced to one of heat exchange between
the sun, the atmosphere, and the earth. The sun, through solar radiation
EA-I. Black: Permafrost as a Natural Phenomenon
(insolation), and the interior of the earth, largely through conduction,
supply practically all primary heat to the surface of the earth (biological
processes, natural or artific
^
i^
al fires, chemical reactions, comic or other
^
✓^
rad
uatnibs
^
iations^
excepted). This primary heat is dissipated to the atmosphere
^
✓^
and to outer space by conduction, radiation, conve
n
^
c^
tion, and evaporation.
^
✓^
The atmosphere by warm winds and precipitation distributes the secondary
heat to the surface of smaller areas.
We know that earth temperatures at the depth of seasonal change are in
most places within a few degrees of the mean annual air temperature, and a
geothermal gradient is established from the surface to the interior of the
earth. The geothermal gradient at any one place is relatively fixed from
year to year, although it varies from place to place and has changed markedly
during geologic time. It is generally considered to be 1°F. for each 60-110
feet of depth in sedimentary rock in the United States (93); possibly 0.1 or
0.2 calorie per square centimeter per day is transmitted to the surface from
the interior (80). In contrast, the sun supplies possibly as much as several
hundred calories per square centimeter per day to the surface, depending
primarily on the season and secondarily on cloudiness, humidity, altitude,
latitude, and other factors. This period of rapid heating, however, is
very short in the Arctic, and for many months heat is dissipated to the
atmosphere and outer space. When dissipation of heat outweighs intake, a
cold reserve is produced. If the ground remains below freezing for more than
2 years, it is called permafrost.
Although the fundamental thesis of the problem is simple, its quanti–
tative solution is exceedingly complex. In only a few isolated areas in
the Arctic have we any information on the geothermal gradients in and below
EA-I. Black: Permafrost as a Natural Phenomenon
permafrost. The climate (including insolation) is so incompletely known
that a present it is not possible to evaluate climatic factors except in
a general way as they effect primary or secondary heat or in dissipation
of heat (37). Thus, the following conditions tend to produce permafrost:
(
1
) long cold winters and short cool summers; (
2
) low precipitation the
year around and especially low snowfall; (
3
) clear winters and cloudy summers;
(
4
) rapid evaporation the year around; (
5
) strong cold winds in summer and
winter; and (
6
) low insolation.
The materials involved have different specific heats and different heat
conductivities (41; 61; 68; 69). Chemical and physical properties vary
widely, yet are of primary importance (69; 75; 76). Water transmits heat
about 25 times as fast as air, and ice 4 times as fast as water. Thus, poorly
drained silt and muck are much more easily frozen than dry, coarse-grained
gravel. Smith (69) points out the marked effect of soil structures and of
architecture of pore space on thermal resistance in natural soils.
The dissipating surface of the earth is even more complex and more
changeable. Water-saturated, frozen vegetation and soil (bare of snow)
serve as active conductors in winter, whereas lush, dry vegetation and dry
porous soil act as excellent insulators in summer. Black-top pavements are
good conductors and heat absorbers in summer and can destroy permafrost. An
elevated and insulated building with circulating air beneath may unbalance
the thermal regime of the ground toward pergelation. Heat conductivities
of some earth materials are known under fixed laboratory conditions, but
the quantitative effect in nature of variable moisture conditions and of
changing vegetation is not. Changes in the volume, composition, or tempera–
ture of ground water or surface runoff have effects as yet little known
qualitatively or quantitatively.
EA-I. Black: Permafrost as a Natural Phenomenon
All these factors must be considered as being in delicate balance between
freezing and thawing. It is to be emphasized that the thermal regime is not
uniform but changes from hour to hour, day to day, week to week, year to year,
and cycle to cycle. Specifically we must think in terms of geographic position,
topography, lithology, structure and texture of soils and bedrock, hydrology,
geothermal gradients, thermal conductivities, vegetation, climate (temperature,
precipitation, cloudiness, wind, insolation, evaporation), and cultural features.
What effect cosmic dust clouds, changes in carbon dioxide content of the
atmosphere, inclination of the earth’s axis, eccentricity of the earth’s orbit,
sun spots, etc., have on permafrost can only be surmised as they
e
^
a^
ffect inso-
^
✓^
lation and dissipation of the earth’s heat
PRACTICAL APPLICATIONS
In the area of permafrost, prior to the construction of buildings, towers,
roads, bridges, runways, railroads, dams, reservoirs, telephone lines, utilidors,
drainage ditches and pipes, facilities for sewage disposal, establishments for
ground-water supply, excavations, foundation piles, or other structures, it is
imperative that the engineer have complete understanding of the extent, thick–
ness, temperature, and character of the permafrost and its relation to its
environment. The practical importance of the temperatures of permafrost cannot
be overemphasized. Knowledge of whether permafrost is actively expanding, is
stabilized, or is being destroyed, is essential in any engineering problem.
Experience has amply demonstrated that low cost or high cost, success or
failure, commonly is based on the degree of understanding of the problems to
be encountered. Once the conditions are evaluated, proper precautions can be
taken with some assurances of success.
EA-I. Black: Permafrost as a Natural Phenomenon
Muller (41) and Liverovsky (39) give comprehensive outlines of general
and detailed permafrost surveys as adapted to various engineering projects.
These outlines include instructions for the planning of the surveys, method
of operation, and data to be collected. Rarely does the geologist or engineer
on a job encounter “cut-and-dried” situations, and it is obvious that discre–
tion must be exercised in modifying the outlines to meet the situation at
hand.
In reconnaissance or preliminary surveys to select the best site for
construction in an area, it is recommended that the approach be one if unravel–ing the natural history of the area. Basically the procedure is to identify
each land form or terrain unit and determine its geologic history in detail.
Topography, character and distribution of materials, type and distribution
of vegetation, hydrology, and climate must be studied as compared with known
areas. Then, inferences, deductions, extrapolations, or interpretations can
be made with reliability commensurate with the type, quality, and quantity
of original data.
Thus the solution of the problems depends primarily on a complete under–
standing of the thermal regime of the permafrost and active layer. No factor
can be eliminated, but all must be considered in a quantitative way. It is
understandable that disagreement exists on what mean annual air temperature
is needed to produce permafrost. Few, if any, areas actually have identical
conditions of climate, geology, and vegetation; hence, they cannot be compared
directly on the basis of climate alone. Without doubt the mean annual tempera–
ture required to produce permafrost depends upon many factors and varies at
least several degrees with variations in these factors. For practical purposes,
however, separate units (terrain units) in the same climate or in similar
EA-I. Black: Permafrost as a Natural Phenomenon
climates may be established on the basis of geology and vegetation. Thus
a basis exists for extrapolating known conditions into unknown areas.
The advantages of aerial reconnaissance and study of aerial photographs
for preliminary site selection are manifold. Aerial photographs in the hands
of experienced geologists, soils engineers, and botanists can supply suffi–
cient data to determine the best routes for roads and railroads; the best
airfield sites; and data on water supply, construction materials, permafrost,
trafficability conditions, camouflage, and other problems. Such an approach
has been used with success by the Geological Survey and other organizations
and individuals (3; 55; 95; 103).
Emphasis is placed on the great need for expansion of long-term applied
and basic research projects on permafrost for a clearer understanding and
evaluation of the problems (33; 41).
Recognition and prediction
of permafrost go hand in hand in a permafrost
survey. If natural exposures of permafrost are not available along cut banks
of rivers, lakes, or oceans, it is in places necessary to dig test pits or
drill holes to obtain undisturbed samples for laboratory tests and to determine
the character of the permafrost.
Surface features can be used with a considerable degree of accuracy to
predict permafrost conditions if the origin of the surface forms is clearly
understood. Vegetation alone is not the solution, but it can be used with
other factors to provide data on surficial materials, surface water, character
and distribution of the permafrost, and particularly on the depth of the
active layer (16; 41; 71; 77).
Cave-in or thermokarst lakes (taw sinks, 29; 3; 41; 95) and ground-ice
mounds (62) are particularly good indicators of fine-grained materials containing
EA-I. Black: Permafrost as a Natural Phenomenon
much ground ice. Polygonal ground can be used with remarkable accuracy also
if the type of polygonal ground and its origin is clearly known. Numerous
types of
Strukturb
o
^
ö^
den
, polygonal ground and related forms have been described
^
✓^
and their origins discussed (9; 28; 58; 63; 96). The type of ice-wedge poly–
gon described by Leffingwell (38) can be differentiated from others on the
basis of surface expression. The author’s work in northern Alaska (1945-48)
revealed that the polygons go through a cycle which can be described as youth,
maturity, and old age--from flat surfaces with cracks, to low-centered polygons,
and finally to high-centered polygons. Size and shape of polygons, widths and
depths of troughs or cracks, presence or absence of ridges adjacent to the
troughs, type of vegetation, and other factors all provide clues as to the
size-grade of surficial materials and the amount of ice in the ground. Frost
mounds, frost blisters, icings, gullies, and many other surficial features
can be used with reliability if all factors are considered and carefully
weighed by the experienced observer.
Geophysical methods of locating permafrost have given some promise
(20; 34; 41; 73; 74). Various temperature-measuring and recording devices
are employed. Augers and other mechanical means of exploring the permafrost
are used (41).
Construction
. Two methods of construction are used in permafrost areas
(41). In one, the passive method, the frozen-ground conditions are undisturbed
or provided with additional insulation so that heat from the structure will
not cause thawing of the underlying ground and weaken its stability. In the
second, the active method, the frozen ground is thawed prior to construction,
and steps are taken to keep it thawed or to remove it, and to use materials
not subject to heaving and settling as a result of frost action. A preliminary
EA-I. Black: Permafrost as a Natural Phenomenon
examination is necessary in order to determine which procedure is more
practicable or feasible.
Permafrost can be used as a construction material (if stress or load
does not exceed plastic or elastic limit), removed before construction, or
controlled outside the actual construction area. Muller (41) has shown
that it is best to distinguish: (
1
) continuous areas of permafrost,
(
2
) discontinuous areas, and (
3
) sporadic bodies. Russian engineers recom–
mend that in (
1
) only the passive method of construction be used; in (
2
) or
(
3
) either the passive or active method be used, depending upon thickness
and temperature of the permafrost. Detailed information and references on
the construction of buildings, roads, bridges, runways, reservoirs, airfields,
and other engineering projects are presented by Huttl (31), Hardy and D’Appolonia
(27), Zhukov (107), Corps of Engineers (88;89), and others.
Eager and Pryor (18) have shown that road icings are more common in
areas of permafrost than elsewhere. They, Tchekotillo (79), and Taber (78)
discuss the phenomena of icings, classify them, and describe various methods
used to prevent or alleviate icing.
One of the major factors to consider in permafrost is its water content.
Methods of predicting by moisture diagrams (
e
^
é^
pures
) the amount of settling
of buildings on thawing permafrost are presented by Fedosov (22).
It should again be emphasized that permafrost is a temperature phenomenon
that occurs naturally in the earth. If man disturbs the thermal regime
know
l
ingly
^
or unknowingly,^
he must suffer the consequences. Every effort should be made to
^
2 words missing. Cf. original p. 26 ✓^
control the thermal regime--to promote pergelation or depergelation as desired.
Generally, the former is difficult near the southern margin of permafrost.
If the existing climate is not cold enough to insure that the permafrost
EA-I. Black: Permafrost as a Natural Phenomenon
remain frozen, serious consideration should be given to artificial freezing
in those places where permafrost must be utilized as a construction material.
Techniques similar to those used at Grand Coulee Dam or on Hess Creek (31)
can be modified to fit the situation. It should be borne in mind that the
refrigerating equipment need only run for a matter of hours during the summer
after the ground has been refrozen and vegetation or other means of natural
insulation have been employed. Bad slides on roads and railroads, settling
under expensive buildings, loosening of the foundations of dams, bridges,
towers, etc., probably can be treated by refreezing artificially at less cost
than by any other method. If fact the day is probably not far off when air–
fields or pykrete (49) or similar material will be built in the Arctic where
no construction materials are available.
Where seasonal frost (active layer) is involved in construction, the
engineer is referred to the annotated bibliography of the Highway Research
Board (43) and to such reports as those of the Corps of Engineers (90; 91).
Water Supply
. Throughout permafrost areas one of the major problems is
a satisfactory source of large amount of water. Problems encountered in
keeping water liquid during storage and distribution or in its purification
are outside the scope of this report. Small quantities of water generally can
be obtained from melted ice or snow. However, a large, satisfactory, annual
water supply in areas of continuous permafrost is to be found only in deep
lakes or large rivers that do not freeze to the bottom. Even then the water
tends to have considerable hardness and organic content. It is generally not
economical to drill through 1,000 to 2,000 feet of permafrost to tap ground–
water reservoirs beneath, although artesian supplied have been obtained under
700 feet of permafrost (15) and under 1,500 feet of permafrost (47).
EA-I. Black: Permafrost as a Natural Phenomenon
In areas of discontinuous permafrost, large annual ground-water supplies
are more common either in perched zones on top of permafrost or in nonfrozen
zones within or below the permafrost (10; 50).
Annual water supply in areas of sporadic permafrost normally is a
problem only to individual householders, and presents only a little more
difficulty than finding water in comparable areas in temperate zones.
Surface water as an alternate to ground water can be retained by earthen
dams in areas of permafrost (31).
Throughout the Arctic, however, the quality of water is commonly poorer
than in temperate regions. Hardness largely in the form of calcium and
magnesium carbonate and iron or manganese is common. Organic impurities
and sulfur are abundant. In many places ground water and surface water have
been polluted by man or organisms.
Muller (4) presents a detailed discussion of sources of water and the
engineering problems of distributing the water in permafrost areas. Joesting
(34) describes a partly successful method of locating water-bearing formations
in permafrost with resistivity methods.
Sewage disposal
in areas of continuous permafrost is a most difficult
problem. Wastes should be dumped into the sea as no safe place exists on
land for their disposal in a raw state. As chemical reaction is retarded
by low temperatures, natural decomposition and purification through aeration
do not take place readily. Large streams that have flowing water throughout
the year are few and should not be contaminated. Indiscriminate dumping of
sewage will lead within a few years to serious pollution of the few deep
lakes and other areas of annual surface water supply. Burning is costly.
EA-I. Black: Permafrost as a Natural Phenomenon
As yet, no satisfactory solution has been found. In discontinuous and sporadic
permafrost zones, streams are larger and can handle sewage more easily, but
even there sewage disposal still remains in places one of the most important
problems.
Agriculture
. Permafrost as a cold reserve has a deleterious effect on
the growth of plants. However, as an impervious horizon, it tends to hold
precipitation in the upper soil horizons, and in thawing provides water from
melting ground ice. Both harmful and beneficial effects are negligible after
1 or 2 years of cultivation, as the permafrost table has thawed beyond the
reach of roots of most annual plants (24).
Farming in areas of permafrost with much ground ice, however, can lead
to a considerable loss in time and money. Subarctic farming can be done only
where a sufficient growing season is available for plants to nature during
the short summers. Such areas are in the discontinuous or sporadic zones of
permafrost. If the land is cleared of its natural insulating cover of vegetation,
the permafrost thaws. Over a period of 2 to 3 years, large cave-in
lakes have developed in Siberia (I. V. Poir
e
^
é^
, oral communication), and pits
and mounds are formed in Alaska (50; 51; 52; 59). The best solution is to
^
s^
elect farm lands in those areas free of permafrost or free of large ground-ice
^
✓^
masses (86).
Mining
. In Alaska, placer miners particularly and lode miners to a
lesser extent have utilized permafrost or destroyed it, as necessary, since
it was first encountered. Particularly in placer mining, frozen ground has
been the factor that made many operations uneconomic (102) or others economic.
In the early part of the century, when gold was being mined so profitably at
Dawson, Fairbanks, Nome, and other places in northern North America, it was
EA-I. Black: Permafrost as a Natural Phenomenon
common for miners to sink shafts more than a hundred feet through frozen
muck to the gold-bearing gravels. These shafts were sunk by steam jetting
or by thawing with fires or hot rocks. If the muck around the shafts or
over the gravels thawed, the mines had to be abandoned.
Now, with the advent of dredges, such ground is thawed, generally with
cold water, one or more years in advance of operations. In the technique
used, holes are drilled through the permafrost at regular intervals of
possibly 10 to 30 feet, depending on the material, and cold water is forced
through the permafrost into underlying permeable foundations or out to the
surface through other holes. Hot water and steam, formerly used, are uneconomi–
cal and inefficient. Where thick deposits of overburden cover placers, they
are removed commonly by hydraulicking. Summer thaw facilitates the process
(48).
Permafrost in lode mining usually is welcomed by the miners as it means
dry working conditions. Its effect on mining operations other than maintaining
low temperatures in the mine is negligible unless it contains aquifers. Because
of low temperatures, sealing aquifers with cement is difficult.
Some well drilling in permafrost requires modifications of existing
techniques and more careful planning for possible exigencies (21). Difficulty
may be encountered in getting proper foundations for the rig. In rotary
drilling difficulty may be experienced in keeping drilling muds at the proper
temperature, in finding adequate water supplies, or proper local material for
drilling muds. In shallow holes particularly, the tools will freeze-in after
a few hours of idleness. Cementing of casings is costly and very difficult
as concrete will not set in subfreezing temperatures. (See also “Arctic
Alaska Petroleum Exploration and Drilling Operations.”) Deep wells extending
EA-I. Black: Permafrost as a Natural Phenomenon
below the permafrost may encounter high temperatures (100° to 150°F.). Hot
drilling muds on returning to the surface thaw the permafrost around the
casing and create a settling hazard in the foundation of the rig and also
create a disposal problem. In some foundations refrigerating equipment must
be used to prevent settling.
Permafrost may act as a tr
o
^
a^
p for oil or even contain oil reservoirs.
^
✓^
The low temperature adversely affects asphalt-base types particularly, and
cuts down yields; production difficulties and costs increase (21).
Refrigeration and Storage
. Excavations are used widely in areas of
permafrost for natural cold storage. They are most satisfactory in continuous
or discontinuous zones. If permafrost is about 30°F., extreme care in ventila–
tion and insulation must be used. Properly constructed and ventilated storerooms
will keep meat and other products frozen for years. Detail
s
^
ed^
plans and charac-
^
✓^
teristics required for different cold storage rooms are described by Chekotillo
(12).
Trafficability
. In the Arctic and Subarctic most travel overland is done
in winter, as muskegs, swamps, and hummocky tundra make summer travel exceed–
ingly difficult (21; 92). Tracked vehicles or sleds are the only practical
types. Wheeled vehicles are unsatisfactory as most of the area is without
roads. Polygonal ground, frost blisters, pinges, and small, deeply incised
thaw streams (commonly called “beaded” streams), rivers, and lakes create
natural hazards to travel.
Permafrost aids travel when it is within a few inches of the surface.
It permits travel of D-8 Caterpillar tractors and heavier equipment directly
on the permafrost. Sleds weighing many tons can be pulled over the permafrost
with ease after the vegetal mat has been removed by an angledozer.
EA-I. Black: Permafrost as a Natural Phenomenon
In areas of discontinuous and sporadic permafrost, seasonal thaw is
commonly 6 to 10 feet deep, and overland travel in summer in many places can
be accomplished only with amphibious vehicles such as the “weasel” of LVT.
^
(Landing Vehicle, Track)^
Travel on foot or by horse is very slow and laborious in many places because
of swampy land surfaces and the necessity for making numerous detours around
slough, rivers, and lakes.
Military
. Permafrost alters military operations through its effects on
the construction of air bases, roads, railroads, revetments, buildings, and
other engineering projects; in its effects on trafficability, water supply,
sewage disposal, excavations, underground storage, camouflage, explosives,
planting of mines; and in other more indirect ways (19; 92). Military
operations commonly require extreme speed in construction, procuring of water
supply, or movement of men and materiel. Unfortunately, it is not always
possible to exercise such speed (21). Large excavations require that natural
thawing, possibly aided by water sprinkling (31), proceed ahead of the earth
movers. Conversely, seasonal thaw may be so deep as to prevent the movement
of heavy equipment over swampy ground until freeze-up. Similarly, it may be
necessary in a heavy building to steam jet piles into permafrost and allow
them to freeze in place before loading them. These things take time, and
proper planning is a prerequisite for efficient operations.
Camouflage is a problem on the tundra. Little relief or change in vege–
tation is available. Tracks of heavy vehicles or paths stand out in marked
contrast for years. In aerial photographs it is easy to see foot paths and
dogsled trails abandoned 10 years or more ago.
The effects of mortar and shell fire, land mines, shaped charges, and other
explosives undoubtedly change as the character of permafrost changes, but no
data are available to the author.
EA-I. Black: Permafrost as a Natural Phenomenon
FUTURE RESEARCH NEEDED
Throughout the foregoing pages brief reference is made to aspects of
permafrost or effects of permafrost on engineering, geologic, biologic, and
other problems for which few factual data are available. However, in the
event that the reader has received the impression that a great deal is known
of permafrost, it is pointed out that the study of permafrost is relatively
young and immature. It has lacked a coordinated and comprehensive investi–
gation by geologists, engineers, physicists, botanists, climatologists, and
other scientists. It is barely in the beginning of the descriptive stages,
and only now is it receiving the world-wide attention it deserves.
As our civilization presses northward, the practical needs of construc–
tion, water supply, sewage disposal, trafficability, and other engineering
problems must be solved speedily and economically. Our present knowledge
is relatively meager, and trial-and-error methods are being used much too
widely. Practical laboratory experiments (75; 76) and controlled experiments
at field stations, such as that at Fairbanks, Alaska (33), are needed in
various situations in the permafrost areas. From these stations methods and
techniques of construction can be standardized and appropriate steps formu–
lated to meet a particular situation. Such laboratories must be supplemented
with arctic research stations such as are found in the Soviet Union. There,
more than 30 natural-science laboratories exist with permanent facilities for
pursuing year-round basic studies in all phases of arctic science. The Arctic
Research Laboratory at Barrow (64) is a start in the right direction. The
academic approach must accompany the practical approach if satisfactory
solution of the problem is to be found.
EA-I. Black: Permafrost as a Natural Phenomenon
To name all the specific topics for future research would make this
article unduly long as no phase of permafrost is well known. However, the
author reiterates that the problems cannot be solved adequately until the
phenomenon of heat flows in all natural and artificial materials in the earth
is understood and correlated with insolation, atmospheric conditions, geother–
mal gradients, and the complex surface of the earth. Then possibly, criteria
can be set up to evaluate within practical limits the effect of various
structures and materials on the dissipating surface of the earth. The
complexities of geology (lithology, structure, and texture of soils and rock),
hydrology, vegetation, and climate of the Arctic make the solution a formidable
task, but the research is an int
i
^
r^
iguing problem for all earth scientists.
^
✓^
EA-I. Black: Permafrost.
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^
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^
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^
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