The Arctic is undergoing rapid transformation due to climate change, leading to an increase in
thermokarst features. A common thermokarst feature in the upland Arctic is channelized
thermoerosional gullies (hereafter called gullies), which commonly form in unchannelized water
tracks, curvilinear zones of increased soil moisture, or in areas of polygonal ground. However,
the transition between unchannelized water tracks and channelized gullies is poorly understood.
The abundance of gullies remains ill-constrained, as well as their topographic characteristics and
hydrological impacts in the upland Arctic. This dissertation addresses these knowledge gaps by
quantifying the abundance, topographic characteristics, and hydrologic impacts of gullies in the
area surrounding Toolik Lake in northern Alaska, USA. To do this, I used a combination of highresolution (1 m) lidar, field-based observations, and two years of water level data from three
hillslope watersheds. In chapter one, I created a lidar-based feature detection model that
identified 4,261 gullies, totaling 7% (738 km) of the hillslope flow network across 431 km2 with
80% accuracy. These gullies were most common in young surficial deposits that contain a finegrained matrix, on steeper slopes, or north or southeastern facing slopes, matching the patterns of
soil pipe development. These results suggest that initial gully formation is driven by a
combination of soil piping and ground ice thaw. The second chapter explored the biophysical
differences between water tracks and gullies and proposed two standardized Arctic gully
definitions: one field-based and one based on remote sensing. Using these definitions, I found
that low-relief gullies (0.60-1.25 m) are four times more common than highly incised gullies
(>1.25 m). This highlights the need for increased research on the impact and abundance of lowrelief gullies in the upland Arctic. The last chapter examines the effects of channelization (i.e., gully presence) on runoff and hillslope hydrology. I found that channelization led to drier
hillslopes and rapid runoff response at our three watersheds, suggesting that an increase in gully
abundance may dry the overall landscape. These findings expand our understanding of gully
formation, abundance, and hydrologic influence in a changing Arctic.
Keywords: Gully abundance, gully formation, permafrost hydrology, landscape change, water
tracks |