Hagafellsjökull is an outlet glacier of the Langjökull ice cap in West-Central Iceland. This surge-type glacier is 7 km long from the terminus to the headwall and up to 6 km wide. The front of the glacier feeds into Hagavatn, a proglacial lake with an elevation of 435 m and an area of 5 km². Currently Hagavatn drains through Nyifoss, a col in the volcanic rocks in the southeast corner of the lake. In the past, this lake has drained through Leynifoss as well, 1.5 km west of Nyifoss. East of the lake is the Jarlhettur subglacial basalt ridge.