This study investigated the surging Hagafellsjökull outlets of the Langjökull ice cap, Iceland. It utilises digital elevation models from 1986, 1997, 2004 and 2007 in order to assess topographic change. These changes are linked to the surging outlets in terms of alteration of the subglacial hydrological system. Flux of water through the subglacial system is considered using a degree day surface melt model. Possible mechanisms of surging are considered and linked to the apparent disparity in surging between the neighbouring outlets Hagafellsjökull Eystri and Hagafellsjökull Vestari. It is found that accumulation in the upper reaches of both outlets led to increased overburden pressure of ice. This resulted in a partial flow switch from the southern Hagafallsjokull outlets to more northern outlets. The loss of flow is considered to have led to instability in the subglacial drainage system resulting in a surge of Hagafellsjökull Eystri and a partial, but failed, surge of Hagafellsjökull Vestari in 1998. Modelled changes in neighbouring subglacial hydrological systems are linked to historic evidence that more outlets of Langjökull ice cap may be, or may have been, surge type. The possibility is suggested that Sudurjökull and Þrístapajökull may well have been subject to surging through alteration of their subglacial hydrological systems, most likely related to the Hagafellsjökull system. The future of Langjökull is considered and agreement is made that the ice cap is retreating with the potential to melt completely within the next 150 years. Future surges seem likely: primarily Hagafellsjökull Vestari is expected to surge within the next 5 years due to increasing imbalance and loss of subglacial meltwater flow. Hagafellsjökull Eystri, post 1998 surge, is also suggested to have returned to a period of quiescence and recent data shows moderate surface elevation increases characteristic of an outlet building up to a surge. Future surge behaviour may also be influenced by increased melting through climatic change and precipitation increases with the possibility of increased surge incidence suggested. The techniques employed are suggested to be useful and highly transable to other studies provided adequate data is available.