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GSA Connects 2023 Meeting in Pittsburgh, Pennsylvania

Paper No. 265-10
Presentation Time: 4:10 PM

INVESTIGATING HYDROGEOCHEMICAL SYSTEMS IN LAVA TUBE CAVES: A STUDY OF A MEROMICTIC LAKE ON THE BIG ISLAND OF HAWAII


ROTZ, Rachel1, CRADDOCK, Robert2, BRIGHAM, Cassandra A.3, RICHARDS IV, David4, SHOZAKI, Hiroki5 and WILDER, Justin1, (1)The Water School, Florida Gulf Coast University, 10561 FGCU Boulevard South, Fort Myers, FL 33965-6565, (2)Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th Street and Independence Ave., SW, Washinton, DC 20560, (3)Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98103, (4)Department of Geology, University of Georgia, Geography-Geology Building, 210 Field Street, Athens, GA 30602, (5)School of Science, Tokyo Institute of Technology, 2 Chome-12-1 Ookayama, Tokyo, 152-8550, Japan

Investigating water within lava tubes offers valuable opportunities for research in cave ecosystems and their importance for Earth and other planetary bodies. This study examines the hydrogeological and geochemical characteristics of an subterranean lake within a lava tube on the Big Island of Hawaii. The lake is located 1.27 km from the coastline, and the opening of the lava tube or “puka” at an elevation of approximately 46 m a.m.s.l. The lake edge occurs inside the lava tube at approximately 20 m a.m.s.l. For a year, fluctuations in lake depth, temperature, and salinity were monitored with in-situ sensors and found to be closely linked with the proximal tidal patterns. Additionally, comparisons with lake depth fluctuations and groundwater elevation data revealed a slight response to rainfall. However, due to the distance between the observation well and the lake, a direct correlation between groundwater changes and lake fluctuations was not evident. The lake exhibits a distinct halocline (5 to 15 ppt), measured with a YSI multiparameter probe at the beginning and end of the research period. The lake reaches a depth of over 20 m towards the back of the cave. An ionic analysis of the major constituents characterizes the water as sodium chloride type with high concentrations of CO32- + HCO3-, Na+ + K+, and Cl-. The presence of a halocline and strong relationship to tides, as well as a slight increase in pH with depth (6.62 to 7.75), suggests that the lake can be characterized as meromictic, with an upper brackish layer receiving water from meteoric sources and gradually becoming more saline as it advances into the transition zone of the exposed, basal freshwater lens, responsive to tides. The unique properties of this lake offer valuable opportunities for ecological and paleo-environmental research, as well as highlight its potential as an analog for planetary research.

Session No. 265

T146. Advances in Monitoring, Mapping, and Modeling Saltwater Intrusion and Groundwater Salinity
Wednesday, 18 October 2023: 1:30 PM-5:30 PM
319 (David L Lawrence Convention Center)
Geological Society of America Abstracts with Programs. Vol. 55, No. 6
doi: 10.1130/abs/2023AM-395507
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