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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 58 (1974)

Issue: 7. (July)

First Page: 1447

Last Page: 1447

Title: Hydrogeology of Cheju Volcanic Island, Korea: ABSTRACT

Author(s): Y. I. Kwon

Article Type: Meeting abstract

Abstract:

A regional groundwater study was conducted on Cheju Island off the Korean coast. Cheju Island comprises about 1,800 sq km (696 sq mi) and is elliptical in shape, with the major axis 74 km long trending in an east-northeast to west-southwest direction; the minor axis, 32 km long, trends in a southwest direction. Mount Halla (1,950 m) is the highest and central crater. Average annual precipitation is estimated to be 1,500 mm (59 in.).

Apart from three streams fed by springs there are no true perennial streams among the 30 streams in Cheju. Thus the low drainage density indicates higher infiltration of precipitation.

Cheju Island is underlain by a succession of basaltic rocks, belonging to the "Inter-Pacific province," interbedded marine sedimentary rocks, and pyroclastic rocks of recent age.

Groundwater occurs locally as perched groundwater and is the source of some springs above the 700-m contour. The existence of a main groundwater table is recognized just above sea level in coastal areas but is assumed to be present farther from the coast. The groundwater tables mostly are unconfined but locally they may be confined by the presence of an aquiclude of local extent. Ninety percent of the springs in Cheju tend to be concentrated in the coastal area.

The porosity of basalts from jointing is assumed to be larger than that from vesicles because specific yield by a pumping test reaches 0.2 and is larger than the effective porosity of the same aquifer as measured in the laboratory.

The best aquifers in Cheju are feldspar olivine basalt and interbedded pyroclastic rocks. Transmissibility ranges from 156 to 20,000 cu m/d/m (1,300 to 1,600,000 gpd/ft) and is ascribed to the irregular development of joints and interconnecting vesicles.

Storage coefficients by pumping test are 0.15-0.3 but generally are assumed to be 0.2. In some coastal areas, as Sinchoon, a confined condition was recognized by the fluctuations of the phreatic water table in harmony with tides.

Analysis of groundwater indicates that the water quality is good for all purposes, domestic, agricultural, and industrial. All groundwater belongs to the calcium-sodium bicarbonate-chloride type with total dissolved solids ranging from 50 to 150 ppm.

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