10:45 〜 12:15
[ACC25-P05] グリーンランド北西部カナック氷河における地中レーダー調査
キーワード：氷河、グリーンランド、GPR
Glaciers and ice caps surrounding Greenland are rapidly losing mass, which affects regional environments as well as global sea level rise. The overview of the glacier changes have been reported based on satellite remote sensing. However, detailed field measurements are required to understand the mechanisms driving the mass loss as well as to develop a numerical model for future projection. To study changes in the peripheral glaciers and ice caps, we have been running field observations on Qaanaaq Ice Cap in northwestern Greenland since 2012 under the projects of GRENE (2012–2016), ArCS (2016–2020) and ArCS II (2020–2025).
Qaanaaq Ice Cap (77º28' N, 69º14' W) has an area of 289 km2 with an elevation range of 30–1110 m. In the summer 2022 (18th July–12th August), we performed a GPR (ground penetrating radar) survey on Qaanaaq Glacier, an outlet glacier of the ice cap. The measurement was performed with a GPR system (SIR-4000, 3200 MFL, GSSI, Inc.) with a central frequency of 40 MHz. Two-way travel time of return signals was converted to the depth by assuming a wave propagation velocity of 168 m s−1 in the glacier. The measurement was carried out along 14 survey routes, i.e. nine sections across the ice flow direction, one long section along the central flowline, and four sections along the side margins (ice divide to the adjacent outlet glaciers). The total length of the survey routes was 21.1 km.
Along the GPR survey routes, the maximum ice thickness of 201 m was found in the upper reach at an elevation of 860 m. The survey across the flowline revealed a V-shaped bed geometry, suggesting erosion of the valley by a stream before the formation of the ice cap. Based on the ice thickness data obtained along the routes, the total ice mass of Qaanaaq Glacier was estimated as 1.2 Gt. In addition to reflections from the bed, strong englacial reflection signals were obtained in the higher elevation area. We interpret the signals are from water-filled crevasses observed on the glacier. In the lower elevation areas, similar signals were generated by supraglacial streams.
Our GPR survey data provided various information (ice thickness, bed geometry and englacial structures), which are important to study physical processes of the glacier as well as to quantify the ice mass. We plan further analysis of the data for thermal structure and hydrology of the glacier and for better understanding of glacier changes in the Arctic.
Qaanaaq Ice Cap (77º28' N, 69º14' W) has an area of 289 km2 with an elevation range of 30–1110 m. In the summer 2022 (18th July–12th August), we performed a GPR (ground penetrating radar) survey on Qaanaaq Glacier, an outlet glacier of the ice cap. The measurement was performed with a GPR system (SIR-4000, 3200 MFL, GSSI, Inc.) with a central frequency of 40 MHz. Two-way travel time of return signals was converted to the depth by assuming a wave propagation velocity of 168 m s−1 in the glacier. The measurement was carried out along 14 survey routes, i.e. nine sections across the ice flow direction, one long section along the central flowline, and four sections along the side margins (ice divide to the adjacent outlet glaciers). The total length of the survey routes was 21.1 km.
Along the GPR survey routes, the maximum ice thickness of 201 m was found in the upper reach at an elevation of 860 m. The survey across the flowline revealed a V-shaped bed geometry, suggesting erosion of the valley by a stream before the formation of the ice cap. Based on the ice thickness data obtained along the routes, the total ice mass of Qaanaaq Glacier was estimated as 1.2 Gt. In addition to reflections from the bed, strong englacial reflection signals were obtained in the higher elevation area. We interpret the signals are from water-filled crevasses observed on the glacier. In the lower elevation areas, similar signals were generated by supraglacial streams.
Our GPR survey data provided various information (ice thickness, bed geometry and englacial structures), which are important to study physical processes of the glacier as well as to quantify the ice mass. We plan further analysis of the data for thermal structure and hydrology of the glacier and for better understanding of glacier changes in the Arctic.