Using Remote Sensing to Understand Icelandic Alluvial Fan Composition as an Analog for a Cold and Wet Ancient Mars

Fan-shaped deposits, including alluvial fans and deltas, are abundant on Mars. They preserve evidence of episodic running water and potentially habitable environments into the early Amazonian. Most alluvial fan analog studies have focused on depositional processes, rather than the composition of fan materials. In particular, it is unclear if the composition of fan deposits represents alteration during transport/deposition or the composition of the watershed in a cold environment.

In this study, we use a suite of remote sensing techniques to characterize mineralogy of rocks and sediments in alluvial fans in Iceland to understand any distinct trends within this tundra climate. This work helps fill a knowledge gap for understanding alluvial fans on Mars through the novel analog study in a cold climate on Earth. Iceland has been widely studied as a Mars analog because of its dominant basaltic composition, general lack of vegetation, and tundra climate. We analyze several alluvial fans of variable morphology, location, and composition to understand how these factors might affect the alteration of fan sediments.

Prior to fieldwork, we analyzed high-resolution orbital images (15 m/pixel) from the World Imagery ESRI Basemap and spectral data (10-60 m/pixel) from the SENTINEL-2 MultiSpectral Instrument in the visible to near infrared (VNIR) range (13 bands; 0.443-2.190 μm) to characterize decameter-scale compositional variability. 

During our July 2024 field season, we imaged fans and their watersheds using a DJI Mavic Pro 2 drone at the meter- to decameter-scale. We used a portable ASD QualitySpec Trek spectrometer to collect VNIR (0.35-2.5 μm) reflectance spectra and identify minerals along transects from the fan apex to toe to capture compositional variability in the fan deposits and their watersheds.

Our results focus on two alluvial fans and their watersheds: one dominated by rhyolite and hyaloclastite in Fjallabak Nature Reserve in the Icelandic highlands and another dominated by basalt near Hoffellsjökull in eastern Iceland. In VNIR spectra from Fjallbak, we observe absorption bands due to hydration (1.4 and 1.9 μm), Fe-oxides (0.53 and ~0.9 μm), and hydrated silica (2.2 μm). At Hoffellsjökull, we also observe kaolinite (2.2 μm doublet) in tan rocks and calcite (2.338 μm) in veins and vesicles within basalt. We also observe broad absorptions near 1 and 2 μm likely due to primary mafic minerals such as olivine, pyroxene, or volcanic glass.

Our results indicate that rocks in the alluvial fans were sourced from a variety of lithologies, which we are able to identify in the watershed using drone and orbiter images. Overall, we do not observe major differences in composition between the fan deposits and their watersheds, suggesting that there is minimal alteration during transport and deposition. Ongoing work includes detailed spectral analyses of sediments along fan transects and comparisons to the watershed to determine how the rocks and sediments vary across the fan deposit. Additionally, comparisons to similar alluvial fans on Mars will improve our understanding of how these features may have formed in a cold climate.