Chemical Changes leading to Soil Formation from Basaltic Bedrock in Reykjanes Peninsula in Iceland

Authors: Gwenyth Heidinger, Dean Wink

Mentors: Peter Jacobs, John Ejnik, Juk Bhattacharyya

Abstract

The Reykjanes peninsula of Iceland has gone through many phases of eruptive activity. Currently, an intense period of volcanic activity is ongoing. It began back in 2021 with the Fagradalsfjall eruption, and is continuing on at Sundhnukur in 2024. Witness accounts date the previous eruptive phase in the peninsula to 1211, now known as the Reykjanes Fires. The chemical composition of these basalts may vary. Recent studies show that the lava at Fagradalsfjall most likely came from the mantle plume and the Sundhnukur eruption from divergent fissure formations released magma from a shallower source. This might create differences in chemistry in the basaltic bedrock. Our goal is to learn how soil forms from basalt. Due to Iceland’s unique geographical location, soil formation processes there are more dependent on original and altered bedrock chemistry, rather than biological activities.

For this project we collected seemingly unaltered and weathered lava samples that erupted during the Reykjanes Fires in Reykjanes, and samples of fresh lava from Fagradalsfjall and Sundnukur to determine overall bedrock chemistry. We also collected samples of hydrothermally altered lava from Fagradalsfjall to search for clay minerals, zeolites and other minerals that could lead to soil formation.

We selected samples based on their alteration colors for Powder X-ray diffraction (PXRD) analysis to compare the chemistry of unaltered and altered lava. Preliminary results indicate presence of magnesium-rich olivine and calcium-rich plagioclase in the unaltered lava from Fagradalsfjall, while hydrothermally altered samples from the same location show presence of Hydromagnesite, Hydroxylclinohumite, Mordenite, and Laumontite. These rapid chemical changes to the bedrock might also be part of the soil formation processes besides slower weathering processes. These results provide insight into the first steps of soil production from basaltic lava in Iceland. This is important for agriculture and soil management. This poster will present our data, analytical methods, and implications of our findings.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5, 2024 doi: 10.1130/abs/2024AM-401990