Determining the Volcanic Eruption Style of Tephra Deposits From Infrared Spectroscopy.

Orbital imagery and spectroscopy at Mars have identified a variety of deposits potentially consistent with volcanic tephra formed during explosive volcanic eruptions, and some of these deposits may have formed due to water‐ or ice‐magma interactions during phreatomagmatic eruptions. If this is the case, these deposits could serve as an additional record of past water on Mars. Previous work has demonstrated that phreatomagmatic tephra is characterized by much lower crystallinities than tephras from other types of eruptions. We hypothesize that crystallinity could be inferred remotely using spectroscopy; however, tephra spectral properties have not been directly linked to their mineralogy. Here, we use Mars analog tephra samples to investigate if eruption styles and the past presence of water during the eruption of possible volcanic deposits on Mars can be determined using orbital spectroscopy. Visible/near‐infrared (VNIR) reflectance and thermal infrared (TIR) emission spectra were collected of basaltic volcanic tephras sourced from a range of eruption styles and deposit types on Earth. Our research demonstrates that, TIR and VNIR data are both sufficient to detect increased glass abundances in volcanic deposits, potentially indicating volatile interactions during an eruption, and that glass‐poor tephras have distinct TIR properties that can be used to infer tephra type (e.g., ignimbrite vs. scoria). Combining VNIR and TIR orbital data for analysis based on our new laboratory spectral endmember library may allow a reevaluation of Martian volcanic and volatile histories using current and future planetary orbital and in situ spectral datasets. Plain Language Summary: Volcanism is a common process across the solar system. Eruptions can become explosive after interactions with water, and the search for current or past water is critical to planetary exploration. Collecting planetary samples to understand what types of eruptions created the volcanic rocks present is not always possible, so we investigate a method for determining volcanic eruption styles that could be completed from orbit. Spectrometers are common instruments on orbiters and can measure the reflection and emission of light from surface materials, including glass. Glass forms in volcanic eruptions when magma quickly cools before minerals can form. We demonstrated that, volcanic deposits from eruptions that were explosive due to interaction with water were glass‐rich and could be distinguished from deposits created in other types of eruptions using data similar to those collected by satellites at Mars. Alteration due to water in the local environment just after eruption is also detectable from orbit. Applying these results to existing or future satellite datasets will provide insight into volcanic eruption styles and environments on planets like Mars. Key Points: The presence of significant glass in volcanic tephras can indicate formation in an explosive phreatomagmatic eruptionVisible/near‐infrared (VNIR) and thermal‐infrared (TIR) spectroscopy can be used together to determine the eruption and cooling history of tephrasA combination of VNIR and TIR orbital spectral datasets would provide insight into the volcanic and volatile histories of Mars and other planets [ABSTRACT FROM AUTHOR]