K. G. Dean

PUFF: A high-resolution volcanic ash tracking model

This paper presents a volcanic ash tracking model referred to as PUFF. The model was developed to simulate the movement of airborne ash in near real-time following an eruption for the purposes of hazard warning. The model tracks particles through a Lagrangian formulation of advection, fallout and turbulent diffusion using a random-walk technique. Three recent eruption events are simulated using archived data. AVHRR images from these events are used for comparison and to validate model results.

Thermal monitoring of North Pacific volcanoes from space

Long-term thermal modeling of volcanoes using satellite imagery provides an effective tool for monitoring remote yet dangerous volcanoes in the North Pacific. This region includes volcanoes in Alaska, the Aleutian Islands, and the Kamchatkan Peninsula. Thermal infrared data collected multiple times per day from weather satellites show distinct signatures for three different types of volcanic activity at different volcanic centers. Near real-time automated techniques are being developed to monitor relative changes in radiant temperature at volcanoes in this region. Radiant temperature values as a function of time are extracted and compared to background values for a series of active volcanoes. By establishing a long-term thermal record for these volcanoes, significant deviations indicative of an impending eruption can be detected. This tool is used to search for precursors to explosive eruptions in order to increase warning times and hazard mitigation for these potentially catastrophic events. A six year archive of satellite imagery has been compiled for this active region, and is available for study.

Deformation of New Trident Volcano measured by ERS‐1 SAR interferometry, Katmai National Park, Alaska

Using Synthetic Aperture Radar (SAR) interferometry, we detect several centimeters of uplift that accumulated during two years (1993–1995) around the vent of the New Trident volcano in Alaskas Katmai National Park. The areas of image coherence correspond to fresh, blocky lavas, while coherence is lost in ash-covered areas. From the uplift gradient we estimate the depth of a pressure source under New Trident volcano to be approximately 0.8–2.0 km. Our results show that in spite of the difficult sub-arctic environment of southern Alaska, strain build-up can be monitored over a two-year period, showing the potential for global monitoring of volcano deformation using SAR interferometry.

Satellite monitoring of remote volcanoes improves study efforts in Alaska

Satellite monitoring of remote volcanoes is greatly benefitting the Alaska Volcano Observatory (AVO), and last years eruption of the Okmok Volcano in the Aleutian Islands is a good case in point. The facility was able to issue and refine warnings of the eruption and related activity quickly, something that could not have been done using conventional seismic surveillance techniques, since seismometers have not been installed at these locations. AVO monitors about 100 active volcanoes in the North Pacific (NOPAC) region, but only a handful are observed by costly and logistically complex conventional means. The region is remote and vast, about 5000 × 2500 km, extending from Alaska west to the Kamchatka Peninsula in Russia (Figure 1). Warnings are transmitted to local communities and airlines that might be endangered by eruptions. More than 70,000 passenger and cargo flights fly over the region annually, and airborne volcanic ash is a threat to them. Many remote eruptions have been detected shortly after the initial magmatic activity using satellite data, and eruption clouds have been tracked across air traffic routes. Within minutes after eruptions are detected, information is relayed to government agencies, private companies, and the general public using telephone, fax, and e-mail. Monitoring of volcanoes using satellite image data involves direct reception, real-time monitoring, and data analysis. Two satellite data receiving stations, located at the Geophysical Institute, University of Alaska Fairbanks (UAF), are capable of receiving data from the advanced very high resolution radiometer (AVHRR) on National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites and from synthetic aperture radar (SAR) equipped satellites.

The 1997 eruption of Okmok Volcano, Alaska: a synthesis of remotely sensed imagery

Abstract Okmok Volcano, in the eastern Aleutian Islands, erupted in February and March of 1997 producing a 6-km-long lava flow and low-level ash plumes. This caldera is one of the most active in the Aleutian Arc, and is now the focus of international multidisciplinary studies. A synthesis of remotely sensed data (AirSAR, derived DEMs, Landsat MSS and ETM+ data, AVHRR, ERS, JERS, Radarsat) has given a sequence of events for the virtually unobserved 1997 eruption. Elevation data from the AirSAR sensor acquired in October 2000 over Okmok were used to create a 5-m resolution DEM mosaic of Okmok Volcano. AVHRR nighttime imagery has been analyzed between February 13 and April 11, 1997. Landsat imagery and SAR data recorded prior to and after the eruption allowed us to accurately determine the extent of the new flow. The flow was first observed on February 13 without precursory thermal anomalies. At this time, the flow was a large single lobe flowing north. According to AVHRR Band 3 and 4 radiance data and ground observations, the first lobe continued growing until mid to late March, while a second, smaller lobe began to form sometime between March 11 and 12. This is based on a jump in the thermal and volumetric flux determined from the imagery, and the physical size of the thermal anomalies. Total radiance values waned after March 26, indicating lava effusion had ended and a cooling crust was growing. The total area (8.9 km 2 ), thickness (up to 50 m) and volume (1.54×10 8 m 3 ) of the new lava flow were determined by combining observations from SAR, Landsat ETM+, and AirSAR DEM data. While the first lobe of the flow ponded in a pre-eruption depression, our data suggest the second lobe was volume-limited. Remote sensing has become an integral part of the Alaska Volcano Observatory’s monitoring and hazard mitigation efforts. Studies like this allow access to remote volcanoes, and provide methods to monitor potentially dangerous ones.

Observations of SO2 production and transport from Bezymianny volcano, Kamchatka using the MODerate resolution Infrared Spectroradiometer (MODIS)

Bezymianny volcano, Kamchatka Peninsula, Russia, is one of the most active volcanoes in the North Pacific (NOPAC) region and erupts violently on average every 6 months. We report the SO2 cloud mass, emission and transport rates for the eruption of Bezymianny on 13–14 January 2004, and discuss the issues associated with determining SO2 production and transfer to the atmosphere from NOPAC volcanoes. During the 13–14 January 2004 eruption, Bezymianny was observed twice by the MODerate Resolution Imaging Spectroradiometer (MODIS) at 0025 and 0210 UTC on 14 January. Using a retrieval based on the 8.6 µm SO2 infrared absorption feature, MODIS yielded a total cloud mass of 34.6±5.19 kt of SO2, an SO2 emission rate of ∼(4.9×103)±(9.12×102) kg s−1, and a transport rate of ∼16.5 m s−1. We tested the sensitivity of the SO2 algorithm to the following input parameters: cloud top height, atmospheric profile, spectral emissivity of the ground and maximum SO2 threshold. The retrieval is sensitive to the atmospheric profile and is particularly dependent on the choice of background emissivity. Multiple background emissivity spectra, obtained over homogeneous backgrounds, reduce errors in the retrieval, when compared to single, less homogeneous emissivity regions.

Satellite analyses of movement and characteristics of the Redoubt Volcano plume, January 8, 1990

Abstract On January 8, 1990 Redoubt Volcano in Alaska erupted. A mushroom-shaped plume formed above the volcano that later drifted to the east, dropping ash on the underlying terrain. The plume was recorded on two satellite images. The images show the plume as being circular 20 minutes after the eruption, and widely dispersed 4 hours later. Digital analyses of the images reveal variations in the morphology and spectral response of the top of the plume. The morphology is attributed to relief features which are related to the ascending motion of the plume. The spectral responses are attributed to variations in the physical characteristics of the plume and to slope-aspect-solar illumination factors. By comparing the two sequential images, the trajectory, velocity and dispersion of the plume were investigated. The height of the plume and the air mass that transported it were determined by comparing pilot reports, radiosonde observations, and plume temperature measurements from satellite images. Results from these analyses will provide a better understanding of what satellite sensors detect and aid development of techniques to track and assess plumes during an eruption.

Analysis of surface processes using SAR data: Westdahl Volcano, Alaska

Seasat, Earth Resource Satellite (ERS-1) and Japan Earth Resource Satellite (JERS-1) Synthetic Aperture Radar (SAR) data were used to investigate surface geomorphic and topographic changes caused by volcanic eruptions of Westdahl Volcano, Alaska. This volcano is located at the west end of Unimak Island, Alaska, approximately 1200 km southwest of Anchorage. This remote, ice-capped volcano has erupted three times in the last 34 years. The eruptions have melted portions of the ice-cap which have been replenished by winter snow. Changes in terrain were studied by comparing seasonal and inter-annual SAR data acquired over a 17 year period prior to, during and after two eruptions. The SAR data provided a record of geological and environmental processes between 1978 and 1995. Time sequential data recorded the formation of landforms and subsequent burial by snow. A series of winter images showed that changing environmental conditions, thought to be predominantly snow moisture, influence the detection and ability to analyse landforms, such as lava flows, by affecting the contrast between features and surrounding ground. Backscatter values of lava flows indicate that it would be difficult to distinguish them solely by radiometric response due to seasonal and annual fluctuations. A colour composite, formed using multi-temporal data, improved the detection of landforms and surface changes related to the eruption as well as environmental changes during the winter.