David A. Rothery

A chronology of the 1991 to 1993 Mount Etna eruption using advanced very high resolution radiometer data: Implications for real-time thermal volcano monitoring

Between December 1991 and March 1993 a continuous effusive eruption at Mount Etna built a 7.6 km2 lava flow field. Flows extended to within 1 km of the town of Zafferana before a successful artificial diversion was carried out higher up the volcano. During this eruption the spaceborne advanced very high resolution radiometer (AVHRR) acquired 308 images on which the activity could be detected. Since these data can be freely and directly available, such coverage potentially allows regular, real-time monitoring. Ground observations and a flow map that we produced using a SPOT image and electronic distance measurement allowed us to develop and test data extraction techniques. AVHRR radiance maps were consistent with known locations of surface activity. These documented the transition from channel to tube fed phases, the changing threat to Zafferana, and flow diversion. Quantitative analysis of the AVHRR data enabled estimation of active lava area, thermal flux, effusion rates, and total flow field volume. Our estimates for eruption rate and total flow field volume, 5.6 to 7.6 m3/s and 220×106 to 300×106 m3, respectively, are in agreement with published ground-based estimates of 5.8 m3/s and 235×106 m3. These correlations demonstrate the high degree of confidence that can now be placed in interpretations of AVHRR time series for eruptions where ground-based data are scanty.

Infrared image analysis of volcanic thermal features: Láscar Volcano, Chile, 1984–1992

Fifteen Landsat Thematic Mapper (TM) images of Lascar volcano (Chile), recorded between December 1984 and April 1992, document the evolution of a lava dome within the summit crater. Four of the scenes were acquired at night. In every image, the two short-wavelength infrared bands, 5 and 7, have detected thermal radiation from the volcano. As a consequence of the Planck distribution function, the relative response of these two channels depends on the proportions of very hot (> 600°C) surfaces occupying tiny pixel areas and broader regions at moderate temperatures (< 280°C). Intercomparison of bands 5 and 7 thereby provides a means for interpreting TM thermal anomalies even in the absence of ground observations. Pronounced changes in the configuration and intensity of the Lascar anomaly suggest that the volcano has experienced at least two cycles of lava dome activity since 1984. The first of these progressed through a “cooling” period, possibly reflecting a reduced flux of magmatic volatiles at the surface, and culminated in an explosive eruption on September 16, 1986, which appears to have completely destroyed the inferred lava dome. The TM data indicate that a new dome had been emplaced by November 1987, more than 15 months before it was first discovered by local observers. Lascars style of cyclical effusive and explosive activity is typical of many volcanoes, and the remote sensing techniques presented herein could be applied elsewhere.

A simple explanation for the space-based calculation of lava eruption rates

Abstract Knowing how lava effusion rates vary during basaltic eruptions can be of great significance when trying to provide preliminary forecasts regarding how far lava will flow. However, problems exist in accurately determining effusion rates using conventional field-based techniques. To ameliorate this problem Harris et al. [J. Geophys. Res. 102 (1997), 7985–8003; Bull. Volcanol. 59 (1997), 49–64; J. Volcanol. Geotherm. Res. 102 (2000), 237–269] developed a method for determining effusion rates using infrared satellite data, and showed how the method could be used to provide realistic estimates of effusion rates, repeatedly during several eruptions at Kilauea (Hawai’i) Krafla (Iceland), Etna and Stromboli (Italy). Harris et al. [J. Geophys. Res. 102 (1997), 7985–8003; Bull. Volcanol. 59 (1997), 49–64] indicate that their method allows instantaneous lava effusion rates to be determined thermodynamically by equating the amount of heat lost by an active lava flow (derived from the satellite data) to the amount of heat liberated by the cooling mass of lava. The purpose of this paper is to provide a simpler, alternative explanation. We find that rather than being used to calculate heat loss, Harris et al. [J. Geophys. Res. 102 (1997), 7985–8003; Bull. Volcanol. 59 (1997), 49–64; J. Volcanol. Geotherm. Res. 102 (2000), 237–269] actually use the satellite data to estimate the area of active lava present within the satellite’s field of view at the movement of data acquisition. Thus, changes in the effusion rates they present can only be proportional to changes in this area. The active flow areas were then multiplied by a constant, the value of which is obtained from a crude approximation of the lava flows heat balance. Crucially, the absolute value of this term falls within the range of an empirically derived parameter that was found by Pieri and Baloga [J. Volcanol. Geotherm. Res. 30 (1986),29–45] to explain strong linear correlations between eruption rate (i.e. the time-averaged effusion rate) and lava flow area for 34 historic Hawaiian flows. As a result, we find that the method of Harris et al. [J. Geophys. Res. 102 (1997), 7985–8003] does not yield instantaneous effusion rates, but instead provides a valid and useful way to estimate average effusion rates (i.e. the eruption rate) from measurements of flow area.

Selection of the landing site in Isidis Planitia of Mars probe Beagle 2

This paper describes selection and characterization of the landing site for the Mars 2004 Beagle 2 mission. The site is within Isidis Planitia between 10°–12°N, 266°–274°W, centered at 11.6°N, 269.5°W. This is at low elevation (-3600 to -3900 m MOLA), is flat (MOLA RMS slope = 0.57°), radar data suggest a smoother surface at decimeter to meter scales than the Pathfinder site and it has a moderate rock abundance (2–17%, mean 11%). In addition to this, Isidis shows evidence for concentration and remobilization of volatiles. In particular, the basin contains conical landforms. We favor models involving the formation of tuff cones during magma-ice interaction. Structures identified as dykes in MOC images may be remnants of magma conduits. The pattern of bulk thermal inertia in Isidis (higher values of 500 Jm-2s-0.5K-1 around the SW-S-E margin decreasing toward the center and north) suggests that an influx of sediment spread from the Noachian areas around the southern half of the basin over the basin floor. The coarse, higher thermal inertia material was deposited closest to the sediment source. The variable state of erosion of the tuff cones suggests that they formed intermittently over a long period of time during Amazonian and possibly Hesperian epochs. Geologically recent resurfacing of Isidis has also occurred by aeolian processes, and this is shown by a deficit in impact craters <120 m diameter. The proportion of rocky material is predicted to be slightly less than the Viking and Pathfinder sites, but there will probably be more duricrust.

Gravity changes and passive SO2 degassing at the Masaya caldera complex, Nicaragua

An understanding of the mechanisms responsible for persistent volcanism can be acquired through the integration of geophysical and geochemical data sets. By interpreting data on micro-gravity, ground deformation and SO2 flux collected at Masaya Volcano since 1993, it is now clear that the characteristically cyclical nature of the activity is not driven by intrusion of additional magma into the system. Rather, it may be due in large part to the blocking and accumulation of gas by restrictions in the volcano substructure. The history of crater collapse and formation of caverns beneath the crater floor would greatly facilitate the trapping and storage of gas in a zone immediately beneath San Pedro and the other craters. Another mechanism that may explain the observed gravity and gas flux variations is the convective overturn of shallow, pre-existing, degassed, cooled, dense magma that is replaced periodically by lower density, hot, gas-rich magma from depth. Buoyant gas-rich magma rises from depth and is emplaced near the surface, resulting in the formation and fluctuation of a low-density gas-rich layer centred beneath Nindiri and Santiago craters. As this magma vigorously degasses, it must cool, increase in density and eventually sink. Five stages of activity have been identified at Masaya since 1853 and the most recent data suggest that the system may have been entering another period of reduced degassing in 2000. This type of analysis has important implications for hazard mitigation because periods of intense degassing are associated with poor agricultural yields and reduced quality of life. A better understanding of persistent cyclically active volcanoes will allow for more effective planning of urban development and agricultural land use.

Volcano detection and monitoring using AVHRR data: the Krafla eruption, 1984

Abstract Abstract. Many volcanic eruptions go essentially unmonitored. Potentially the Advanced Very High Resolution Radiometer (AVHRR), with its global coverage, frequent return period, and sensitivity in the thermal infrared, represents a data source capable of monitoring surface volcanic activity unrecorded by ground observations or other satellite sensors. In this study an attempt is made to demonstrate this potential by extracting information for the 1984 eruption at Krafla, Iceland. Seven cloud-free AVHRR images were available for the 14 day period of eruptive activity. The surface activity was detectable as a major thermal anomaly in all three of the longer wavelength channels and was vigorous enough during one night-time pass to be detectable in the near-infrared channel (0.725-1.1μm). Channel 2 and 4 radiance data were used to calculate the size and temperature of sub-pixel heat sources within the lava flow field, and a heat source at 1050° C was estimated as occupying an area of approximately 24...

Long‐lived explosive volcanism on Mercury

The duration and timing of volcanic activity on Mercury are key indicators of the thermal evolution of the planet and provide a valuable comparative example for other terrestrial bodies. The majority of effusive volcanism on Mercury appears to have occurred early in the planets geological history (~4.1–3.55 Ga), but there is also evidence for explosive volcanism. Here we present evidence that explosive volcanism occurred from at least 3.9 Ga until less than a billion years ago and so was substantially more long-lived than large-scale lava plains formation. This indicates that thermal conditions within Mercury have allowed partial melting of silicates through the majority of its geological history and that the overall duration of volcanism on Mercury is similar to that of the Moon despite the different physical structure, geological history, and composition of the two bodies.

Thermal distributions at fumarole fields: implications for infrared remote sensing of active volcanoes

Abstract Multispectral satellite data recorded in the short-wavelength infrared (SWIR) region have been used to estimate temperatures of hot volcanic features such as fumaroles and lava bodies. This has required the assumption that thermal distributions across the surfaces in question can be adequately represented by a very few (usually two) temperature components. We investigate here the applicability of such simple descriptions to fumarole fields, an important class of thermal phenomena. Our surface temperature surveys, conducted at Momotombo (Nicaragua) and Vulcano (Italy), suggest that SWIR emission from the interiors of high-temperature fumarole vents far exceeds that from their surroundings. In contrast, cooling crust on active lava bodies can contribute more SWIR radiation than the small areas of exposed incandescent material that are often present. Such a distinction should be discernible in the relative response of the two Landsat Thematic Mapper (TM) SWIR bands, providing a basis for identification of the volcanic nature of thermal anomalies in Landsat TM or similar data, even in the absence of field observations. However, estimates of subpixel temperatures and heat flux, made from such satellite data, must be considered unreliable.

Analysis of Airborne Visible/Infrared Imaging Spectrometer (AVTRIS) data of volcanic hot spots

Abstract In July 1991, the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was flown over Mount Etna and Stromboli, Italy. At the time, magma-filled vents, of subpixel dimensions, occupied the summit craters of both volcanoes. For pixels located over these hot spots, thermal radiation dominates the sensor response between about 1-4 and 2-4 μm, the latter figure being the upper limit of spectral coverage. One thermal source within the Northeast Crater of Mount Etna is evident at wavelengths as short as I 0 μm despite this intensity, therc is no saturation of the AVIRIS sensors because of their wide dynamic range. A curve-fitting algorithm is used to match the thermal spectra with Planck radiation models, in order to derive information on temperature distributions at the subpixel scale. Difficulties arise because the sequential readout of detector elements during scanning leads to interband spatial misregistration. Although the standard preprocessing of AVIRIS data includes a linear interpolation of...

Mechanisms of explosive volcanism on Mercury: Implications from its global distribution and morphology

The identification of widespread pyroclastic vents and deposits on Mercury has important implications for the planets bulk volatile content and thermal evolution. However, the significance of pyroclastic volcanism for Mercury depends on the mechanisms by which the eruptions occurred. Using images acquired by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, we have identified 150 sites where endogenic pits are surrounded by a relatively bright and red diffuse-edged spectral anomaly, a configuration previously used to identify sites of explosive volcanism. We find that these sites cluster at the margins of impact basins and along regional tectonic structural trends. Locally, pits and deposits are usually associated with zones of weakness within impact craters and/or with the surface expressions of individual thrust faults. Additionally, we use images and stereo-derived topographic data to show that pyroclastic deposits are dispersed up to 130 km from their source vent and commonly have either no relief or low circumpit relief within a wider, thinner deposit. These eruptions were therefore likely driven by a relatively high concentration of volatiles, consistent with volatile concentration in a shallow magma chamber prior to eruption. The colocation of sites of explosive volcanism with near-surface faults and crater-related fractures is likely a result of such structures acting as conduits for volatile and/or magma release from shallow reservoirs, with volatile overpressure in these reservoirs a key trigger for eruption in at least some cases. Our findings suggest that widespread, long-lived explosive volcanism on Mercury has been facilitated by the interplay between impact cratering, tectonic structures, and magmatic fractionation.