Infrared Spectroscopy of Melts: New Approaches to Understanding Lava Flow Emplacement

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

The products of volcanic eruptions commonly include airborne glassy ash, and gases such as sulfur dioxide, water vapor and carbon dioxide. The ash and gas can pose hazards to distant populations as well as overflying aircraft, as was evident during the recent eruption of Eyjafjallajökull in Iceland. Eruptions can also produce lava flows, lava domes and pyroclastic flows that are hazardous mostly to nearby population centers. Examples of this style of activity were seen at the recent eruptions of Mt. St. Helens (WA) and Mt. Spurr (AK) as well as at the ongoing eruption at Kilauea (HI). The fundamental goal of this research is to better understand volcanic eruption processes by studying the surfaces of these lava flow and domes. Lava domes can erupt as gas-rich rocks with a range of bubble and glass contents alternating between lava extrusion and hazardous explosive eruptions. In contrast, basaltic lava flows are emplaced at much higher temperatures and rapidly form a chilled glassy crust after exposure to air. Because it is commonly too risky to collect hand samples directly during a volcanic eruption, quantitative remote detection techniques have become extremely valuable. Being able to determine more than the temperature of a flow surface allows one to constrain the eruption conditions through determination of the mineral, volatile and vesicle percentages. It is planned to use thermal infrared (TIR) data collected in the field and in the laboratory to analyze these glassy lava surfaces. Both glass and vesicles have a detectable effect on TIR data, however this effect has not been well quantified nor is the fundamental physics of TIR emission from molten surfaces well understood. In order to carry out this research, a first of its kind micro-furnace assembly at the Department of Geology and Planetary Science, University of Pittsburgh will be employed. This furnace (fabricated under previous NSF funding) is capable of melting rock samples and is directly attached to a laboratory emission spectrometer. It will allow the spectral effects of glass and vesicles to be quantified in TIR data. A similar procedure will be used at the active lava flows of Kilauea volcano, HI using a TIR camera specially adapted to collect data in multiple spectral wavelength bands. This will allow a direct comparison between the lab and field data (as well as TIR data collected from orbit). The research will provide the first systematic characterization of the diagnostic spectral band positions and shapes of these materials and apply those results to better understand the small scale processes ongoing as a lava flow is emplaced and cools. This research has immediate implications on the physics of how lava flows cool and risks involved with how fast they are emplaced. In addition, an automated field-based TIR monitoring system will be developed based on the TIR camera, which will aid in volcanic hazard monitoring of flows and domes around the globe. To quantitatively understand the TIR signal from natural lava domes, critical laboratory- and field-based data are needed. The TIR wavelengths are sensitive to the characterization of silicate material because of the presence of strong absorption bands (dominantly Si-O and also Al-O) in the clear region of the Earth's atmosphere (~ 8-12 micrometers; 1250-833 cm-1). In order to accurately analyze the emitted spectra and quantitatively extract the fundamental physical properties of the lava (e.g., surface vesicularity, the phenocryst and glass composition/percentage and temperature) it is necessary to understand the spectral effects of the glassy crusts and molten material. This work will provide the first systematic characterization of the diagnostic absorption band positions and spectral shapes of these materials and is divided into two primary tasks. The first task is laboratory-focused with the goal of providing the first systematic characterization of the diagnostic TIR absorption band positions/shapes of basaltic glasses and melts. Specifically, they will focus on three states in the laboratory studies: (1) samples above the solidus and the glass transition temperatures, (2) the glassy crusts that initially form on lava and mineral melts upon cooling, and (3) the final interstitial matrix glass of mineral and natural samples. They will collect the full TIR spectral range of the laboratory spectrometer (5-25 micrometers or 2000-400 cm-1), but concentrate on the region of the Earth's atmospheric window (8-12 micrometers region or 1250-830 cm-1) in order to compare the data directly to those collected by satellite and from the field. The second task is field-based with the goal of developing TIR instrumentation capable of collecting similar TIR data and which can eventually be deployed as a monitoring tool. The data collected from the multispectral TIR camera should allow validation of the laboratory results using data collected from active basaltic flows. This will be the first time such a camera will be used in this way and the hope is that it will lead to eventual construction of a rugged monitoring instrument capable of deployment on remote volcanoes and used for monitoring and derivation of fundamental physical properties of lava domes and flows in real time. The proposed research will advance our understanding of infrared spectroscopy, molecular-scale glass and melt structure, and surface processes on both active and inactive lava flows.