ICE IN LAVA TUBES FROM WEST-CENTRAL NEW MEXICO AS ARCHIVE OF PAST VOLCANIC ERUPTIONS AND CLIMATE CHANGE

The Southwest in the United States is currently in a megadrought phase. Recent studies have shown that three of the most severe droughts of the last two millennia have occurred in the last 120 years, while geo-archeological evidence suggests there were five megadroughts just from 150 to 950 CE. Now, climatologists try to better understand the causes to the droughts across the Southwest. A 110-cm long ice core was drilled from an ice deposit in a lava tube from El Malpais National Monument, New Mexico. Stable isotope analysis was conducted on 50 samples collected at ~2 cm interval from the ice core. Ranges for the δ¹⁸O values were from

–11.78 to –3.54‰, while the δ²H values vary between –74.9 and –10.5‰. The source of water in the ice deposit depends on whether the rainfall/snow is driven by the winter climate variability related to ENSO or the Pacific/North American pattern or originates from the North American Monsoon. The evaluation of the stable isotope’s values served a vital role in uncovering the moisture source. Similar studies on ice cores from El Malpais have also helped construct a climatic chronology of the past 2000 years. The ancestral Puebloan communities across the pre-colonial Southwest melted ice from El Malpais’ lava tubes during periods of extensive droughts. The abundance of charcoal littered throughout the lava tubes, and within the ice itself are evidence of this indigenous pre-colonial exploitation. Tracer element geochemistry (IC-MS and ICP-MS) was also applied to the ice core to measure anions (e.g., SO₄^2-) and cations (e.g., Na⁺) in an attempt to refine the chronology using past volcanic eruptions. This study, and the techniques used within it, would provide paleoclimatologists with important information of the Southwest’s current and past climactic state.