Causes and Consequences of Hazardous Lava-Water Interactions, with Particular Focus on Rootless Eruptions

  • Frances Boreham

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Lava-water interactions (LWI) occur in many different environments, causing secondary hazards, but are not routinely considered in hazard assessments. The variety of deposits from explosive LWI (known as rootless eruptions) reflects the range of eruption dynamics. However, the influences of lava flux, water availability and sediment properties on triggering and sustaining rootless eruptions are poorly understood.

Contemporary accounts of the 1783{1784 Laki Fissure eruption highlight the range of hazardous LWI, including lava dams, flooding, disruption of water supplies, and rootless eruptions. The presence of rootless cones around flooded areas shows how lava and water interact to modify the environment, increasing the risk of rootless eruptions in previously dry areas.

A case study of the Younger Laxa Lava in northeast Iceland, which inundated a shallow lake, river gorge and broad glacial valley, shows the relationship between local lava flux, water availability and rootless cone morphology. Areas with abundant water and high local lava flux build large scoriaceous rootless cones. Areas with less water create smaller scoriaceous cones, spatter cones and hornitos. Reduced lava flux, e.g. at flow margins, also results in smaller cones. However, similar analysis of Laki rootless cones shows that the relationship between cone size and environment is not straightforward and depends on the local conditions and sediment properties.

Numerical models show that conduction from a lava flow to a saturated underlying sediment can raise pore pressure enough to trigger a rootless eruption. Sediment permeability controls the rate of pressure build up: coarse, high permeability sediments allow steam to escape as it is generated; high{moderate permeability sediments allow steam to escape as the lava advances, but pressure can rise tens of metres behind the flow front; very low permeability sediments prevent steam escape and drive explosions that disrupt the lava flow advance.
Date of Award21 Jan 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorKatharine V Cashman (Supervisor) & Alison C Rust (Supervisor)

Cite this