2:30 PM - 2:45 PM
[ACC32-04] Optical televiewer observation of the borehole of Kongsvegen Glacier in Svalbard
Keywords:Glacier, Svalbard, Glacial sediment, Subglacial environment, Borehole camera
The internal structure of glaciers provides valuable information about the processes of glacier flow with sediment intrusion into the ice as an important feature. However, direct observations are rare especially near the glacier bed because the access is difficult. To investigate the structure of glacier ice and included sediments, we performed an optical televiewer observation at a tidewater glacier in August 2024. Here we report the preliminary analysis of images obtained in a borehole drilled to the base of the glacier.
Kongsvegen (78°48’N, 12°59’E) is a ~100 km2 tidewater glacier in Svalbard, flowing into Kongsfjorden. Kongsvegen is a surge-type glacier, currently in the quiescent phase. The last surge was in 1948, but the glacier is gradually accelerating since 2016, a survey location near the equilibrium altitude was moving at ~40 m a–1 in 2022 whereas it was ~5 m a−1 in 2005–2015. Because the glacier is underlain by a soft-sediment layer, the glacier ice near the bed potentially includes sediments entrained during the process of glacier flow.
In August 2024, we drilled to the glacier bed using a hot-water drill and reached the base at 361-m depth. We performed borehole observation by using a televiewer BIP-6 (Raax Co. Ltd.), which captures 360-degree lateral view with a cone-shaped mirror in the probe. The system contains a digital magnetometer inside to account for the probe rotation in the borehole. We captured the image for full length of the borehole, with the resolutions of ~1 mm for vertical/lateral directions.
The televiewer captured different types of layers in the glacier, distinguishable by brightness variations that result from amounts of included bubbles. Sediment layers were observed at 245–361 m depth. We counted 64 individual sediment layers from visual inspection of the televiewer images. The distance between the layers decreases towards the deeper region. The southward dip was the dominant direction from the sediment layers, which corresponded with the direction of thrusting which is expected from the northward flow direction of the glacier. Our result yield direct information about the sediment distribution within the glacier and shows the unexpected existence of sediment layers more than 100 m above the bed, implying the complexity of processes of the sediment entrainment at the base.
Kongsvegen (78°48’N, 12°59’E) is a ~100 km2 tidewater glacier in Svalbard, flowing into Kongsfjorden. Kongsvegen is a surge-type glacier, currently in the quiescent phase. The last surge was in 1948, but the glacier is gradually accelerating since 2016, a survey location near the equilibrium altitude was moving at ~40 m a–1 in 2022 whereas it was ~5 m a−1 in 2005–2015. Because the glacier is underlain by a soft-sediment layer, the glacier ice near the bed potentially includes sediments entrained during the process of glacier flow.
In August 2024, we drilled to the glacier bed using a hot-water drill and reached the base at 361-m depth. We performed borehole observation by using a televiewer BIP-6 (Raax Co. Ltd.), which captures 360-degree lateral view with a cone-shaped mirror in the probe. The system contains a digital magnetometer inside to account for the probe rotation in the borehole. We captured the image for full length of the borehole, with the resolutions of ~1 mm for vertical/lateral directions.
The televiewer captured different types of layers in the glacier, distinguishable by brightness variations that result from amounts of included bubbles. Sediment layers were observed at 245–361 m depth. We counted 64 individual sediment layers from visual inspection of the televiewer images. The distance between the layers decreases towards the deeper region. The southward dip was the dominant direction from the sediment layers, which corresponded with the direction of thrusting which is expected from the northward flow direction of the glacier. Our result yield direct information about the sediment distribution within the glacier and shows the unexpected existence of sediment layers more than 100 m above the bed, implying the complexity of processes of the sediment entrainment at the base.