著者

川又 基人 菅沼 悠介 土井 浩一郎 澤柿 教伸 服部 晃久

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.3, pp.315-336, 2020-06-25 (Released:2020-07-11)

参考文献数

69

被引用文献数

2

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The purpose of geomorphological studies in East Antarctica is to understand past fluctuations of the Antarctic Ice Sheet, which is essential to constrain ice sheet models and predict future behavior of the East Antarctic Ice Sheet. Here we show a deglacial history of Skarvsnes, at the southern part of the Soya Coast, East Antarctica based on a geomorphological field survey and newly obtained surface exposure ages. Bedrock higher than ca. 250 m a.s.l. at the northwest part of Skarvsnes (Skjegget) is weathered extensively, whereas bedrock below ca. 250 m a.s.l. is relatively unweathered. The degree of weathering of bedrock above 250 m a.s.l. is similar to that at the northern part of the Soya Coast, which is thought to have been ice-free throughout the last glacial period. Therefore, a clear difference in the degree of weathering depending on altitude probably indicates the lower limit of the ice sheet elevation during the last glacial period at Skarvsnes. Judging from the multiple directions of glacial striae, the ice sheet covering the area retreated while changing flow direction under the influence of the bedrock topography after the last glacial period. Since ca. 9 ka, the ice sheet is thought to have thinned and eventually divided into two major ice streams (northward and southward) that were obstructed by a 362 m a.s.l. mountain (Shirasuso-Yama), at the southeastern part of Skarvsnes. However, the timing of the initiation of the ice sheet retreat and its duration remain unclear. Therefore, additional surface exposure ages from various areas and heights at Skarvsnes are required for a detailed reconstruction of the ice retreat history and to understand its mechanism.

著者

福田 洋一 服部 晃久 奥野 淳一 青山 雄一 土井 浩一郎

出版者

日本測地学会

雑誌

測地学会誌 (ISSN:00380830)

巻号頁・発行日

vol.68, pp.1-13, 2022 (Released:2022-05-18)

参考文献数

29

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National Institute of Polar Research (NIPR) has been conducting absolute gravity measurements not only at Japanese Antarctic research station, Syowa since early 1990s, but also other foreign research stations in Antarctica recently. To validate the absolute gravimeter employed, test measurements were conducted at the gravity point located at the machine shop in NIPR usually before and after the measurements in Antarctica. The observed gravity values at the point, however, often varied exceed the expected instrumental errors. To explain the causes of the large gravity variations, we compared the observed gravity values with the precipitations at three AMeDAS(Automated Meteorological Data Acquisition System)stations, groundwater levels at a Tokyo Metropolitan Government observatory, and the height data at four GEONET (GNSS Earth Observation Network System)stations. The result of the comparisons showed that 1) the seasonal or shorter gravity variations were mainly caused by the precipitations and the resultant soil moisture and/or shallow groundwater changes, and 2) the secular or longer period gravity variations were explained by the uplift after the 2011 Tohoku-oki earthquake and the long-term variations of the groundwater level at deeper depths. After removing these effects, the standard deviation of the gravity residuals was less than 3 µGal (1 µGal=10−8 m/s2).