Notes from the Field

Written by Holly Valgardson.

I am holding a very large peridotite mantle xenolith. I am a second-year master's student working with Dr. Ben Black in the Earth and Planetary Science department. This past July 2024, I had the amazing opportunity to conduct ten days of fieldwork in Lanzarote, Canary Islands, with another lab group from Queens College, the City University of New York. We focused on the Timanfaya eruption (1730-1736), the second-largest historic basaltic fissure eruption recorded in the last thousand years, which destroyed 26 villages and covered 146 square kilometers of the island. The Timanfaya eruption consisted of five phases, with explosive activity in the initial phase and primarily effusive activity in the later four phases. This eruption offers the opportunity to further my research in studying magma ascent rates and their connection to eruption styles and explosivity.

Using a hammer and chisel to collect some fresh lava from one of the flows.Our fieldwork involved hiking up each of the ten volcanic cones from the five phases and collecting tephra, lava, and xenolith samples, which we can later analyze in the lab. We also conducted mantle xenolith size distribution surveys, noting variations in sizes and abundance in peridotite mantle xenoliths across all five phases. Mantle xenoliths are dense rocks formed deep in the mantle and brought to the surface during eruption. They are literally beautiful bright green chunks of the Earth’s mantle! By quantifying these xenoliths, we can estimate magma ascent rates, as these rocks are denser than the surrounding magma, and if the magma is moving slowly towards the surface xenoliths should sink rather than making it to the surface. In other words, the larger the xenolith is, the faster the ascent rate. Future work in my research also aims to measure ascent rates by analyzing the melt within olivine crystals found in the volcanic tephra.

This fieldwork provides valuable insights into volcanic processes. Not only does this fieldwork deepen our understanding of the six-year eruption, but assessing and predicting timescales of volcanic eruptions and understanding eruption style and explosivity are essential for assessing volcanic hazards in volcanically active areas, especially those that are inhabited. This fieldwork has enhanced my skills as a geologist, and I am beyond excited to                                                                     do more in the future!