2024 年 42 巻 p. 113-121
Basal ice motion is a key process in glacier flow, playing a crucial role in fast glacier motion and short-term ice speed variations. However, the mechanisms of basal motion remain poorly understood because direct observations are sparse. This paper reports the design and performance of a “ploughmeter” developed for deployment in a borehole to observe glacier basal motion and subglacial hydrology. The device measures three-dimensional acceleration and water pressure with sensors enclosed in a metal tube of 34 mm in diameter and 2.5 m in length and with a weight of 8.0 kg. Installed at the bottom of a borehole, the ploughmeter is dragged over the glacier bed as a result of glacier basal motion, which enables the study of signals related to basal motion and subglacial materials. Laboratory tests were conducted to investigate acceleration signals, which exhibited distinct characteristics depending on the material being ploughed. The ploughmeter showed stick-slip motion in gravel, with a tilting rate during the stick phase that correlated with the speed of the ploughing. The results suggest that the ploughing observations provide insight into subglacial materials and variations in basal ice motion. When the device is placed on a glacier surface, the seismic signals correlate with those obtained by a conventional seismometer in terms of the number of seismic events (r＝0.74) and the tremor amplitude (r＝0.54). Therefore, the ploughmeter offers an opportunity for measuring subglacial seismicity near the source location at the glacier base.
