Detection and Monitoring of Jokulhlaup-Induced Topographic Changes Using NASA ATM Lidar Data: Skeidararsandur, Iceland

Skeidararsandur, southern Iceland, sustained severe erosional and depositional damage from a catastrophic volcanically-triggered glacial outburst flood or jokulhlaup from November 5-7, 1996. Active parts of this site are continuing to experience daily centimeter- to meter-scale accretion and erosion. Jokulhlaups exert a significant influence on sandur evolution through erosion, transport and deposition of sub-glacial and pro-glacial sediments. Flood inundation extent can normally be monitored by conventional remote sensing. However, centimeter-scale elevation changes caused by fluvial erosion or deposition are costly and time-consuming to obtain in the field, especially over large areas such as occurred in the 1996 event. Here, we show that lidar (LIght Detection And Ranging) remote sensing technology has great potential for providing such information. NASA's Airborne Topographic Mapper (ATM) laser altimeter was deployed in 1996, 1997, 1998 and 2001, allowing direct measurement of centimeter-scale elevation changes caused by the 1996 jokulhlaup, as well as subsequent normal flows and smaller flood events. A careful assessment of ATM`s performance was conducted by detailed ground surveys. The ATM sensor acquired swaths (normally about 250 m wide) of highly precise topographic measurements with typical posting of 2-5 m, and a vertical precision of 10-15 cm. An E-W transect close to the coastline crossing major rivers was measured by ATM before (June 1, 1996) and after (May 6-7, 1997) the event. A Comparison between the ATM profiles shows that this event substantially reshaped the terrain, with more deposition (a depth of 25 cm over a distance of 35 km) than erosion (23 cm over 4.6 km). The 2001 ATM profile (May 19 2001) suggests that the fluvial system is recovering to its pre-flood level, flushing away the flood deposit at a rate of 2.4 cm/year. Digital elevation models (DEMs) of 5 m resolution were produced for the years 1997 and 2001. Both DEMs are of high quality and detail, with both fluvial landforms and human structures clearly evident.