대한지리학회지 (Journal of the Korean Geographical Society)

대한지리학회 (The Korean Geographical Society)
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우주기원 방사성 핵종을 이용한 만어산 암설지형의 침식률 및 노출연대 측정

Application of In-situ Produced Cosmogonic $^{10}$ Be and $^{26}$ Al for Estimating Erosion Rate and Exposure Age of Tor and Block Stream Detritus: Case Study from Mt. Maneo, South Korea

  • Yeong Bae Seong (Dept. of Geography Education, Seoul National University) ;
  • Jong Wook Kim (Dept. of Geography Education, Seoul National University)
  • 발행 : 2003.06.01
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초록

우주 기원의 방사성 핵종(核種)은 근래에 지형연구에 널리 활용되고 있다. 본 연구에서는 우주 기원의 방사성 핵종인 $^{10}$ Be과 $^{26}$ Al를 이용하여 만어산의 토르와 암괴류를 대상으로 그 구성 암석의 지표 노출 연대와 침식률을 측정하였다. 연구 결과, 토르는 적어도 약 6만 5천년 전, 그리고 암괴류는 적어도 3만 8천년 전에 노출된 것으로 나타났다. 한편, 토르와 암괴류의 구성 암석의 표면 침식률은 각각 9m/Ma 15m/Ma인 것으로 나타났다. 이러한 침식률의 차이는 풍화 및 침식에 대한 국지적인 조건이 다르기 때문인 것으로 생각된다. 특이한 점은, 산정부에 위치한 토르의 구성 암석들 중 일부가 $^{26}$ Al/$^{10}$ Be과 $^{10}$ Be를 이용하는 Lal (1991)이 밝힌 정상상태 침식구역(steady-state erosion island)에서 벗어나 있는데 이것은 이 토르의 표면이 비정상적인 침식의 경로를 겪었다는 것을 의미하며 본 연구에서는5cm-60cm 정도의 표면이 여러 번 떨어져 나갔다는 것으로 판단된다.

CRN (Cosmogenic radionuclide) methodology has been a versatile tool applicable to a wide range of geomorphology. This study was underiaken to ascertain the rate of erosion and exposure age of mountain-top detritus (tors and block streams) on Mt. Maneo by employing the concentrations of in-situ produced cosmogenic $^{10}$ Be and $^{26}$ Al from bedrock surfaces that are exposed to cosmic rays. The results suggest that tors on the summit were positioned here during the glacial period but no later than 65ka and block streams have been stabilized also since the last glacial period but no later than 38ka. The tors on the summit have been eroded at a slower rate (9m/Ma) than blocks on the hillslope (15m/Ma) since the initial abrupt exposure of each landform to cosmic rays, suggesting that there is a slight difference in the rate of erosion between the summit and the hillslope, and that the local relief between the two areas has been increased. When the $^{26}$ Al/$^{10}$ Be-$^{10}$ Be concentrations from samples are plotted in Lal's steady-state erosion island, one sample (from a for) has complex exposure histories, which can be explained by the occurrence of multiple chipping event of 5cm to 60cm in length on the surface of the rock.

키워드

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