Gully formation in the McMurdo Dry Valleys, Antarctica: multiple sources of water, temporal sequence and relative importance in gully erosion and deposition processes DicksonJames L. HeadJames W. LevyJoseph S. MorganGareth A. MarchantDavid R. 2017 Close-up of punctuated activity in Gully A during December 2010, showing <i>c</i>. 10 cm of fan emplacement and several metres of lateral erosion of pre-existing fan material. Vantage point shown in Figure 4c (Site 3).