Short communication Origins and implications of zigzag rift patterns on lava lakes Leif Karlstrom a , Michael Manga b, ⁎ a Department of Physics, University of Oregon, Eugene, OR 97403, USA b Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA Received 7 September 2005; received in revised form 18 January 2006; accepted 30 January 2006 Available online 23 March 2006 Abstract The distinctive rift patterns observed on newly formed lava lakes are very likely a product of interaction between heat transfer (cooling of lava) and deformation of the solid crust in response to applied stresses. One common pattern consists of symmetric “zigzag” rifts separating spreading plates. Zigzags can be characterized by two measurable parameters: an amplitude A, and an angle θ between segments that make up the zigzags. Similar patterns are observed in analog wax experiments in which molten wax acts as cooling and solidifying lava. We perform a series of these wax experiments to find the relationship between θ, A, and the cooling rate. We develop a model to explain the observed relationships: θ is determined by a balance of spreading and solidification speeds; the amplitude A is limited by the thickness of the solid wax crust. Theoretical predictions agree well with experimental data; this enables us to scale the model to basaltic lava lakes. If zigzag rifts are observed on the surface of lava lakes, and if physical properties of the lava crust can be measured or inferred by other means, measurements of θ and A make it possible to calculate crust-spreading velocity and crust thickness. © 2006 Elsevier B.V. All rights reserved. Keywords: lava lakes; rifting; solidification; pattern formation 1. Introduction The surface of lava lakes consists of rigid plates separated by rifts filled with hotter, fluid magma. The pattern and dynamics of these plates on lava lakes has been used to better understand several geological processes. For example, the evolution of surface patterns and the velocity of plates can be used to study convective regimes in the interior of the lava lake (e.g., Harris et al., 2005). Because cooling causes solidifica- tion and hence a change in rheology from liquid-like to solid-like, the interaction of the plates on the surface of lava lakes has also served as a model for global plate tectonics (e.g., Duffield, 1972). Finally, patterns on terrestrial lava lakes provide a template for interpreting surfaces features on Jupiter's moon Io (e.g., Radebaugh et al., 2004). Often the rifts make distinctive patterns, forming jagged lines at an angle to the direction of crustal spreading. Fig. 1 shows one common pattern: a “zigzag” rift in which the rift width is constant, and the angle with a line perpendicular to the spreading direction is the same for every kink in the rift. If we know the mechanism that makes zigzag rifting patterns, we can estimate the physical features of the newly formed crust, and therefore gain a better understanding of the geological processes at work. Ragnarsson et al. (1996) observed similar rifting patterns in an investigation of spreading wax layers. Fig. Journal of Volcanology and Geothermal Research 154 (2006) 317 – 324 www.elsevier.com/locate/jvolgeores ⁎ Corresponding author. Fax: +1 510 643 9980. E-mail addresses: lkarlstr@gladstone.uoregon.edu (L. Karlstrom), manga@seismo.berkeley.edu (M. Manga). 0377-0273/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2006.01.004