Thermal precursors in satellite images of the 1999 eruption of Shishaldin Volcano

Abstract

Shishaldin Volcano, Unimak Island Alaska, began showing signs of thermal unrest in satellite images on 9 February 1999. A thermal anomaly and small steam plume were detected at the summit of the volcano in short-wave thermal infrared AVHRR (advanced very high resolution radiometer) satellite data. This was followed by over 2 months of changes in the observed thermal character of the volcano. Initially, the thermal anomaly was only visible when the satellite passed nearly directly over the volcano, suggesting a hot source deep in the central crater obscured from more oblique satellite passes. The "zenith angle" needed to see the anomaly increased with time, presumably as the thermal source rose within the conduit. Based on this change, an ascent rate of ca. 14 m per day for the thermal source was estimated, until it reached the summit on around 21 March. It is thought that Strombolian activity began around this time. The precursory activity culminated in a sub-Plinian eruption on 19 April, ejecting ash to over 45,000 ft. (13,700 m). The thermal energy output through the precursory period was calculated based on geometric constraints unique to Shishaldin. These calculations show fluctuations that can be tied to changes in the eruptive character inferred from seismic records and later geologic studies. The remote location of this volcano made satellite images a necessary observation tool for this eruption. To date, this is the longest thermal precursory activity preceding a sub-Plinian eruption recorded by satellite images in the region. This type of thermal monitoring of remote volcanoes is central in the efforts of the Alaska Volcano Observatory to provide timely warnings of volcanic eruption, and mitigate their associated hazards to air-traffic and local residents.

Assessing Performance of the RSTVOLC Multi-Temporal Algorithm in Detecting Subtle Hot Spots at Oldoinyo Lengai (Tanzania, Africa) for Comparison with MODLEN

“…In addition, in our case, we analyzed only nighttime scenes further reducing the probability of detecting short-lived events occurring in daylight conditions. • Satellite viewing geometry: Weak thermal activities (e.g., minor intra-crater eruptions) generating hot spots of low temperature and/or spatial extent are more difficult to identify from space when satellite data are acquired under unfavorable viewing conditions (i.e., high zenith angles) (e.g., [7]). …”

“…For many decades, thermal remote sensing techniques have been used to monitor active volcanoes [1][2][3][4][5][6][7][8][9][10][11][12]. In remote and inaccessible regions, where in situ instruments are often lacking, satellite observations may represent the only source of available information (e.g., [7,13,14]).…”

“…In remote and inaccessible regions, where in situ instruments are often lacking, satellite observations may represent the only source of available information (e.g., [7,13,14]). …”

Heat and SO2 Emission Rates at Active Volcanoes - The Case Study of Masaya, Nicaragua

“…Thermal anomalies have proved to be precursors of a number of eruptive events (e.g. Andronico et al, 2005;Dean et al, 2004;Dehn et al, 2002), and once an eruption begins, temperature plays a major role in lava flow emplacement and lava field development (e.g. Ball et al, 2008;Calvari et al, 2010;Lodato et al, 2007).…”

On the Exportability of Robust Satellite Techniques (RST) for Active Volcano Monitoring

“…Several satellite techniques have been proposed until now to identify and track volcanic ash plumes [e.g., [2][3][4][5][6][7][8][9][10][11], as well as to detect and monitor volcanic hot spots [e.g., [12][13][14][15][16][17][18][19][20][21][22][23], using data provided by both polar and geostationary satellites. An original multi-temporal approach, named RST-Robust Satellite Technique [24], already successfully used to study both volcanic phenomena [9][10][11][25][26][27][28], has been implemented in an automatic system developed in IMAA-DIFA laboratories (Institute of Methodologies for Environmental Analysis-Department of Engineering and Physics of the Environment), to monitor Italian volcanoes in near real time.…”