Paleoecological
significance of the Jilmoe Bog (alopine peat)
in the Odaesan
National Park
Park, Kyeong
Korean National Parks
Authority, Seoul, 121-717
Introduction
The wetland is ecologically very
important habitat for diverse organisms. In this paper, the author try to
elucidate the morphogenetic environment of Jilmoe Bog (alpine peat) found in
the high etch plain (1,060 m.a.s.l).
The term thermokarst was first proposed
by the Russian M. M. Ermolaev in 1932 to describe irregular, hummocky terrain due
to the melting of ground ice. Subsequently, the term has been applied
specifically to the process of ground ice melt accompanied by local collapse or
subsidence of the ground surface. The meaning of thermokarst has rapidly
enlarged to include not only the process of subsidence and collapse but also a
large number of more complex activities.
Under stable climatic conditions,
thermokarst develops in response to a variety of geomorphic and/or vegetational
conditions. These conditions may be either natural or human-induced. One
example of natural cause is the presence of polygonal ice-wedge systems. In
summer, water accumulation occurs in the central trough above the thermal
contraction cracks, or at the junction of ice wedges, or within low-centered
polygons. These shallow bodies of standing water invariably favour more
intensive thawing during warm seasons and impede the winter freezing. Once
initiated, the concentration of water in summer and snow in winter increases.
The depression grows larger, thus promoting further thaw of the ground without
any supplementary agents. This phenomenon has been known as 'self-developing
thermokarst'.
Geomorphic and palynological
investigation indicate that the Jilmoe Bog has been originated from the
thermokarst processes of the last glacial age.
Materials and methods
Study site
The Jilmoe Bog is located in the subalpine etchplain where so-called
Deabo Granite which had intruded in Jurassic epoch of Mesozoic era (c.a. 146
M.A) (Fig. 1, 2)
|
Figure 1. Physiography
of Jilmoe Bog |
|
Figure 2. Location of
study area in 19th century map. |
The annual mean temperature of study area is 5.3¡É,
the annual mean precipitation reaches 2,888mm. The minimum temperature of the
coldest month (January) is below -30¡É and the depth of frozen
soil is over 1.6m.
|
Table 1. Meteorological data along the altitude gradient
in the Vicinity of Jilmoe Bog
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Moisture
balance around the Jilmoe Bog study site has been calculated using Thornthwaite
formula(Thornthwaite and Mather, 1957). The results are shown in table 2.
|
Table 2. Moisture balance table in Jilmoe Bog
|
Results
Geomorphology of the study area
In 1941 Lautensach reported the presence
of striped terrace and turf-banked terraces at the Mt. Baekdoo. Kim (1966)
reported the fossil involution at the slope of Mt. Acha in Seoul. Kim (1970)
reported the earth hummocks and turf-banked terraces in Mt. Halla. Chang (1983)
reported the presence of a block fields at the bottom of the cliff Chottae-bong
in Mt. Jiri. According to his report, gneiss blocks are scattered at around
1680m a.s.l. on the slope angled at 7.5¡Æ. He regarded the
observed angular blocks are frost-shattered mountain-top detritus which is
originally core stone. Two high altitude terraces in Mt. Jiri (1600~1650,
1650~1700) has been regarded to be originated from the cryoplanation in
periglacial environment (Chang, 1983).
One of the vegetated periglacial forms is
characterized by the presence of peat or ice lenses inside the hummocks. Peat
may also fill in the troughs in between the hummocks("peat rings").
As opposed to sorted forms on bare surfaces, the nonsorted ones are developed
owing to frost penetration under vegetation and/or turf mantle of tundra. The
tension due to freezing makes the mantle convex, humps and hummocks appear, their
regular occurrence being marked by the term "cemetery hummocks."
A particular type of patterned ground,
largely dependent on the action of frost, is represented by the so-called
string bogs. These are peat bogs with an undulating surface. Jilmoe Bog consists
of a large bog and a small bog. The large bog is 63m long and 42m wide. The
basal surface of Jilmoe Bog is uneven (Figure 3). As discussed earlier, Jilmoe
Bog is a string bog formed due to thermokarst action. In string bogs, its
surface is wavy with stepped dry hills and net-like troughs crossing hill
slope. It seems that string bog is related to the permafrost of cold conifer
forest zone, where the depth of frozen soils is very deep in winter at least.
|
Figure 3. Plane view
of the Jilmoe Bog |
There can be found turf-banked terracettes of width 30-40cm in the
headwall of small cirque-type nivation hollow around Jilmoe Bog. These
turf-banked teracettes are formed by the frost growth of soil water under the
grass mat in periglacial environment.
Palynological analysis of the study area
The results of sedimentological and palynological investigations
indicate that peat deposits in the Jilmoe Bog has been formed since the onset
of warm climate during the early Holocene. Sandy layer including some pebbles
has been overlain by the peat. These sandy layer seems to be the product of the
periglacial shattering during the late Pleistocene (Fig.4).
|
Figure 4. Global
Pleistocene Plant Communities |
Considering the arboreal pollen dominate among AP, NAP, and spores, Jilmoe Bog seems to be formed in early
Holocene when the tree species became dominant plants around the study area. In
pollen zone I, oak trees including Quercus dominate. This palynological
reconstruction study goes well with the moderm vegetation compostion of the
area. In pollen zone II, the ratio of
Gramineae, Artemisia, and
Umbelliferae increases reflecting the increase of human intervention.
References
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