Inventory and kinematics of active and transitional rock glaciers in the Southern Alps of New Zealand from Sentinel-1 InSAR

In this study, we inventoried and mapped the active and transitional rock glaciers in the central part of the Southern Alps, New Zealand, using Sentinel-1 InSAR (interferometric synthetic aperture radar) data. We used forty-three interferograms acquired between 2015 and 2019 with time intervals between six days and two years along with orthoimage analyses. A total of 123 rock glaciers were identified, of which 40 are active; that is, displaying velocities higher than 10 cm/yr. The remaining landforms are considered transitional. Among the complete sample of rock glaciers inventoried, 9 may also be interpreted as debris-covered glacierets. The number of inventoried landforms is low compared to what is observed in other similar mountain ranges, such as the European Alps. We explain this by the reduced vertical extent of the periglacial belt and the generally steep topography often not favorable for rock glacier development. Additionally, the motion rates appear relatively low. We hypothesize that a mean annual air temperature at the rock glacier locations well above 0°C is the main reason for this. These conditions may have resulted in significant ground ice melt. Rock glaciers in the Southern Alps are thus in an inactivation phase, which is expressed by typical morphologies such as stable fronts.

本研究利用哨兵-1号干涉合成孔径雷达（Sentinel-1 InSAR，interferometric synthetic aperture radar）数据，对新西兰南阿尔卑斯山中部的活动型与过渡型岩冰川（rock glaciers）进行了清查与制图。研究采用2015至2019年间获取的43幅干涉图，其时间间隔介于6天至2年之间，并结合正射影像（orthoimage）分析开展工作。本次研究共识别出123处岩冰川，其中40处为活动型岩冰川，即运动速率高于10厘米/年的岩冰川；剩余地貌均被归为过渡型。在所清查的全部岩冰川样本中，另有9处可被视为碎屑覆盖微型冰川（debris-covered glacierets）。与欧洲阿尔卑斯山等其他同类山系的观测结果相比，本次清查的地貌数量偏少。研究将这一现象归因于冰缘带（periglacial belt）的垂直范围有限，且普遍陡峭的地形通常不利于岩冰川的发育。此外，岩冰川的运动速率也相对偏低。我们提出假说：岩冰川所在区域的年平均气温远高于0℃，是导致该现象的核心原因。此类环境条件或已引发大量地下冰融化。因此，南阿尔卑斯山的岩冰川正处于失活阶段，其典型表现为稳定前缘等特征性地貌形态。