SPATIAL DISTRIBUTION OF BASALTIC ROOTLESS CONES AS A FUNCTION OF WATER AVAILABILITY: ICELANDIC AND EXPERIMENTAL STUDIES

Rootless cones can form from the interaction of lava with wet ground and are often clustered in topographic lows. On the Laki flow in Southern Iceland, Hamilton et al.(2010) found that spatial distribution within clusters of cones may indicate competition for water resources during cone formation. Cones forming with less available water are more likely to be uniformly distributed than cones with more water, which may have random or clustered spatial distributions. It is important to better understand how lava-water interactions form rootless cones in order to identify areas vulnerable to phreatic eruptions, as well to identify lava-water features on Mars or other planets.

Six rootless cone clusters on the post-glacial Younger Laxárhraun flow in Northeastern Iceland were analyzed. Two of these were plotted with reconnaissance mapping, while the others were mapped in Google Earth. Cone centroids were calculated in ArcMap, and Geologic Image Analysis Software was used to determine spatial distributions of the cones. Based on the geologic history of the area, it was assumed that the location and elevation of water bodies has not changed since 2,000 years ago.

The site farthest from bodies of water had uniformly distributed cones. Regardless of water proximity, three of the other sites had randomly distributed cones, while two exhibited clustered distributions. These results suggest the influence of factors other than water proximity, although uniform distributions and less water were found to correlate in two experimental flows created for this study at the Syracuse University Lava Project (http://lavaproject.syr.edu), where molten basalt from a gas-fired tilt furnace was poured over saturated sand.

In Iceland, elevation above the water table may impact rootless cone spatial distribution more than lateral distance to bodies of water. Rootless cones located on distal lava lobes can appear clustered due to flow morphology. Clearly, future work encompassing more sites is necessary to better characterize factors involved in rootless cone development.

Reference:

Hamilton, Christopher W., Sarah A. Fagents, and Thorvaldur Thordarson. "Explosive Lava-Water Interactions II: Self-Organization Processes among Volcanic Rootless Eruption Sites in the 1783-1784 Laki Lava Flow, Iceland." Bull. Volcanol. 72 (2010): 16.