Surface Elevation Variations on Lachman II Debris-covered Glacier (Ice-cored Rock Glacier), James Ross Island, Antarctic Peninsula, and Its Responses to Recent Climate Change

James Ross Island, Antarctic Peninsula, has recently experienced severe climate change: warming from the 1970s until the early 2000s and cooling from the early 2000s until around 2014. Lachman II, a 2-km long debris-covered glacier (ice-cored rock glacier) , is located at the northern part of James Ross Island. On Lachman II, the surface elevation lowered at a rate of 1.1 and 0.7 m a(-1) at the center of the upper stream of the debris-covered area from 1992 until 1995. However, in response to the cooling trend from the early 2000s until around 2014, the surface lowering rate temporarily slowed to 0.2 and 0.4 m a(-1) for at least seven years from 2008 to 2015 at the center of the upper stream of the debris-covered area. In response to extremely high air temperatures in 2016, the glacier surface lowered again, accelerating to 0.5 and 0.6 m a(-1) from 2015 to 2017. A ground penetrating radar (GPR) image displayed a reflection plane along the longitudinal section of the glacier, which indicates that a debris-rich ice layer was thrusting up from the glacier bottom. The origin of the upward thrust is supported by the fact that the surface rock debris consists mainly of sandstone and mudstone derived from the bottom of the glacier.