Paleoecological significance of the Jilmoe Bog (alopine peat)
in the Odaesan National Park
Korean National Parks Authority, Seoul, 121-717
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
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
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
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.
Chambers, F. M. (ed.). 1993. Cliamte Change and Haman Impact on the Landscape - Studies in paleoecology and environmental archaeology. Chapman & Hall. 303 p.
Chang Ho. 1983. Periglacial landforms in the eastern part of the main ridge of Mt. Jiri, South Korea. Geography. Korean Geographical Society. 27: 31-50.
Clark, M. J. (ed.). 1988. Advances in Periglacial Geomorphology. John Wiley & Sons. 481 p.
Embleton, C. and King, C. A. M. 1968. Glacial and Periglacial Geomorphology. Edward Arnold, 608 p.
French, H. M., 1996, The Periglacial Environment 2nd edition, Longman, 341 p.
Jeon, Y.G. 2000. A study on the boulder stream of granitoid in Korea. Journal of the Korean Association of Regional Geographers. 6 (2): 71-82.
Kalvoda, J. and Rosenfeld, C. L. (eds.). 1998. Geomorphological Hazards in High Mountain Areas. Kluwer Academic Press. 314 p.
Washburn, A. L. 1979. Geocryology - A Survey of Periglacial Processes and Environments. Edward Arnold. 406 p.