Characteristics of mountain glaciers in the northern Japanese Alps
Abstract. In 2012, three perennial snow patches in the northern Japanese Alps were determined to be very small glaciers (VSGs: < 0.5 km2). These were soon followed by four more nearby. However, it had not been determined how such glaciers could be maintained in such a warm climate. In this study, we calculate annual and seasonal mass balances of five of these VSGs, covering 2015–2019 for four of them (2017–2019 for the fifth) using multi-period digital surface models (DSMs) based on structure from motion–multi-view stereo (SfM–MVS) technology and images taken from a small airplane. The results indicate that, due to mass acquired from avalanches, these VSGs are maintained by acquiring a winter balance that is more than double that from the snowfall amount, thereby exceeding the summer balance. Therefore, we classify them as topographically controlled VSGs. We find almost no annual fluctuation in their summer balance; however, their winter balance, and annual balance, have large annual fluctuations. The annual balance, which mainly depends on the winter balance, showed accumulation throughout each glacier during heavy snow years and ablation throughout each glacier during light snow years. This characteristic differs from the upper accumulation area and lower ablation area that exists on most glaciers. These VSGs had negative annual balance gradients, which suggests that they did not have an equilibrium line during the observation period. Moreover, comparing to other glaciers worldwide, we find the mass balance amplitude of glaciers in the northern Japanese Alps to be the highest measured to date.