Reconstruction of the largest Holocene jokulhlaup within Jokulsa a Fjollum, NE Iceland

Glacial outburst floods (jokulhlaups) have a significant role for landscape evolution in NE Iceland. A number of jokulhlaups have routed from the northern margin of Vatnajokull during the Holocene. In this study, reconstruction of the largest Holocene jokulhlaup along Jokulsa Fjollum, NE Iceland was undertaken using the HEC-RAS hydraulic modelling and HEC-GeoRAS flood mapping techniques with a Digital Elevation Model (DEM) derived from ERS-InSAR data and field-based wash limit evidence. The largest jokulhlaup produced extensive erosional and depositional landforms across an inundated area of similar to 1390km(2) and is calculated to have had a peak discharge of 0.9 x 10(6) m(3) s(-1). Power per unit area within this jokulhlaup varied from 6 to 46,000 W m(-2). Jokulhlaup hydraulics are related to geomorphogical evidence at three key sites: in Vaoalda, Upptyppingar and Moorudalur sub-areas in order to explain the abrupt spatial variation of the flood characteristics on a regional scale and to relate erosional and depositional features to spatial variations in jokulhlaup hydraulics. These process-form relationships of the largest jokulhlaup along the Jokulsa A Fjollum are compared with large outburst floods elsewhere. The largest Jokulsa a Fjollum jokullalaup had a factor of similar to 20 times smaller discharge and similar to a factor of 20 times lower power per unit area than Altai palacoflood-the largest known flood on the Earth. (c) 2005 Elsevier Ltd. All rights reserved.