Basaltic lava flow characterization and modelling using a geomorphological approach: integration of field and drone acquired data (Krafla, Iceland)

Krafla is located in the Mývatn region (North-East Iceland), on the axis of the Icelandic rift valley. The last episode of intense activity, examined in this study, remains the most important in the site’s history, and is called the ‘Krafla fires’ (1975-1984). Like most of Icelandic volcanoes, the Krafla eruptions are fissural and produce tholeiitic basaltic lavas (Nicholson, 1990).

The aim of this study is to determine whether it is possible to simulate a basaltic flow that is consistent to the reality in the field, based on morphologies observed in the field and on a very high-resolution numerical model. The focus of this study is an auxiliary flow, 605 m long and covering 0.04 km², positioned at the southern end of the main Krafla flow. In the field, variations in width (spreading and channeling) and thickness (in the centre and at the edge of the flow) were assessed at regular intervals. These were supplemented by a high-resolution drone survey of the upstream part of the flow (300 m), covering 0.05 km². The georeferenced pictures were computed to generate a Very High-Resolution Digital Surface Model (2 cm). The internal rheological parameters, such as yield stress and viscosity, are determined using the morphological approaches presented by (Chevrel et al., 2013) : The first approach evaluates these two parameters for Newtonian and Bingham behaviour. The second approach is based on lateral spread, excluding slope-related effects. Finally, the third approach evaluates these parameters in the context of channelized flows.

Field observations show that this bayonet-shaped flow has a range of thicknesses from 35 cm to 3.5 m. It has an average width of 48.5 m (with a minimum width of 15.7 m and a maximum width of 75.8 m) and slopes between 4° and 21°. In addition, upstream to downstream, the facies tend to have an increasingly rough and disturbed texture as they approach the flow terminations. Regarding internal parameters: these 3 approaches show a convergence of viscosity values between 2.1 and 4.2.10³ Pa.s with ranges of values between 0.5 and 11.10³ Pa.s ; and yield strength values which tend to converge towards 1.9 to 6.0.10³ Pa with ranges of values between 0.9 and 105.10³ Pa. Those orders of magnitude are consistent with the values obtained by  (Chevrel et al., 2013) for other cases of the spreading of icelandic basaltic flows.

This study provided an initial assessment of the morphological and rheological characteristics of a basaltic flow, based on field observations and high-resolution numerical models. Internal parameters such as viscosity and yield strength were assessed using several morphological approaches, yielding values consistent with similar studies carried out on other icelandic basaltic flows. Exploratory use of numerical simulation would allow further refinement of the model's internal parameters and external parameters, in order to assess and rank their relative influence on emplacement behavior.

Chevrel, M.O., Platz, T., Hauber, E., Baratoux, D., Lavallée, Y., Dingwell, D.B., 2013. Earth and Planetary Science Letters, volume 384, p. 109-120. DOI : 10.1016/j.epsl.2013.09.022

Nicholson, H., 1990. university of Edinburgh. 301 p.