Landscape reaction, response, and recovery following the catastrophic 1918 Katla jökulhlaup, southern Iceland

Abstract

One of the largest recorded glacier outburst floods (jökulhlaups) occurred in 1918, generated by the last major subglacial eruption of Katla volcano in southern Iceland. Using digitized historical topographic surveys and field observations from the main proglacial outwash plain (Mýrdalssandur), we document the reaction of Mýrdalssandur to the 1918 event and subsequent response and recovery. Our analysis highlights the longevity of elevated topography, over the recovery period, and the complete reorganization of the main perennial meltwater channel system, both of which will affect and condition the flow routing and impact of future jökulhlaups. The jökulhlaup deposited approximately 2 km 3 of sediment onto Mýrdalssandur immediately after the event and extended the coastline by several kilometers. However, 80% of this material by volume has since been removed by surface and subsurface water flow on the main sandur and by marine reworking at the coast. By 2007, the surface elevation at specific locations on the outwash plain and the position of the coastline were similar to those in 1904, indicating near-complete recovery of the landscape. Despite this, the Mýrdalssandur coastline has experienced net advance over the past 1000 years. Using our calculated characteristic landscape response and recovery values following the 1918 event (60 years and 120 years) we deduce that the landscape has been in a dominant state of transience, with regard to forcing frequency and timescale of recovery, over the past 1000 years, which has facilitated long-term landscape growth.

GLOFs in the WOS: bibliometrics, geographies and global trends of research on glacial lake outburst floods (Web of Science, 1979–2016)

“…Various aspects of jökulhlaups on the Katla volcano, Iceland, are elaborated in 27 research items (e.g. Duller et al, 2014). The most famous glacial lakes in GLOF hazard/risk studies nowadays -Imja Tsho, Tsho Rolpa (both Nepal Himalayas) and Palcacocha (Peruvian Andes) -have received the attention of 17, 9 and 7 research items, respectively (e.g.…”

GLOFs in the WOS: bibliometrics, geographies and global trends of research of glacial lake outburst floods (Web of Science, 1979–2016)

“…Various aspects of jokulhlaups on the Katla volcano, Iceland, are elaborated in 27 research items (e.g., Duller et al, 2014). The most famous glacial lakes in GLOF hazard / risk studies nowadays -Imja Tsho, Tsho Rolpa (both 25…”

Bar deposition in glacial outburst floods: scaling, post-flood reworking, and implications for the geomorphological and sedimentary record

“…Warburton (1994) has shown that for a relatively small rainstorm flood the braided channel produced during the flood was re-converted to a single channel in one melt season. A long-term analysis of landscape recovery following the very large 1918 Katla outburst flood (Duller et al, 2014) shows that in terms of net change in volume of sediment added or subtracted to the outwash plain the landscape recovered in approximately 120 years. Despite this, the landscape is still recognisably impacted by the 1918 jökulhlaup (Russell et al, 2010) and sedimentary deposits of the flood are still preserved (Duller et al, 2008).…”

“…Despite this, the landscape is still recognisably impacted by the 1918 jökulhlaup (Russell et al, 2010) and sedimentary deposits of the flood are still preserved (Duller et al, 2008). This outcome may be because a large portion of the sediment removal was due to removal by groundwater exfiltration rather than erosion of surface deposits (Duller et al, 2014). Of the recent jökulhlaups to have occurred in Iceland, the largest and most spectacular was the November 1996 jökulhlaup on Skeiðarársandur (Russell and Knudsen, 1999;Russell et al, 2006).…”

“…It is too soon to assess the full postflood recovery of the 1996 Skeiðarársandur jökulhlaup and determine what the final geomorphological and sedimentary record of this event will comprise. However, the long-term analysis of the 1918 Katla jökulhlaup indicates that the pattern of landscape recovery from large jökulhlaups is broadly negative exponential, with the most rapid changes occurring in the first few decades (Duller et al, 2014). The study by Smith et al (2006) of elevation changes in the flood channels for the first five years following the 1996 jökulhlaup is therefore useful in describing the initial recovery and indicating the likely trajectory of future changes.…”