Bulletin of Volcanology

, Volume 72, Issue 4, pp 449–467

Explosive lava–water interactions I: architecture and emplacement chronology of volcanic rootless cone groups in the 1783–1784 Laki lava flow, Iceland

  • Christopher W. Hamilton
  • Thorvaldur Thordarson
  • Sarah A. Fagents
Research Article

DOI: 10.1007/s00445-009-0330-6

Cite this article as:
Hamilton, C.W., Thordarson, T. & Fagents, S.A. Bull Volcanol (2010) 72: 449. doi:10.1007/s00445-009-0330-6


To determine the relationships between rootless cone emplacement mechanisms, morphology, and spatial distribution, we mapped the Hnúta and Hrossatungur groups of the 1783–1784 Laki lava flow in Iceland. We based our facies maps on Differential Global Positioning System (DGPS) measurements, photogeological interpretations, and supporting field observations. The study area covers 2.77 km2 and includes 2216 explosion sites. To establish the timing of rootless cone formation we incorporated tephrochronological constraints from eighty-eight stratigraphic sections and determined that the Hnúta and Hrossatungur groups are composite structures formed by the emplacement of six geographically and chronologically discrete domains. Rootless eruptions initiated in domain 1 on the first day of the Laki eruption (June 8, 1783) and lasted 1–2 days. The second episode of rootless activity began in domain 2 on June 11 and lasted 1–3 days. The four domains of the Hrossatungur group dominantly formed after June 14 and exhibit a complex emplacement sequence that reflects interactions between the Laki lava, contemporaneously emplaced rootless cones, and an existing topographic ridge. In the study area, we identify three distinct rootless cone archetypes (i.e., recurring morphological forms) that are related to tube-, channel-, and broad sheet lobe-fed eruptions. We assert that emplacement of lava above compressible substrates (e.g., unconsolidated sediments) may trigger rootless eruptions by causing subsidence-induced flexure and failure of the basal crust, thereby allowing molten lava (fuel) to come into direct contact with groundwater (coolant) and initiating analogs to explosive molten fuel–coolant interactions (MFCIs).


Volcanic rootless conesPseudocratersPhreatomagmaticExplosive lava–water interactionsLakiIcelandMars

Supplementary material

445_2009_330_MOESM1_ESM.pdf (802 kb)
Appendix 1(PDF 801 kb)

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Christopher W. Hamilton
    • 1
  • Thorvaldur Thordarson
    • 2
  • Sarah A. Fagents
    • 1
  1. 1.Hawai‘i Institute of Geophysics and PlanetologyUniversity of Hawai‘iHonoluluUSA
  2. 2.School of GeosciencesUniversity of EdinburghEdinburghUK