Current and future use of TOPSAR digital topographic data for volcanological research

In several investigations of volcanoes, high quality digital elevation models (DEM's) are required to study either the geometry of the volcano or to investigate temporal changes in relief due to eruptions. Examples include the analysis of volume changes of a volcanic dome, the prediction of flow paths for pyroclastic flows, and the quantitative investigation of the geometry of valleys carved by volcanic mudflows. Additionally, to provide input data for models of lava flow emplacement, accurate measurements are needed of the thickness of lava flows as a function of distance from the vent and local slope. Visualization of volcano morphology is also aided by the ability to view a DEM from oblique perspectives. Until recently, the generation of these DEM's has required either high resolution stereo air photographs or extensive field surveying using the Global Positioning System (GPS) and other field techniques. Through the use of data collected by the NASA/JPL TOPSAR system, it is now possible to remotely measure the topography of volcanoes using airborne radar interferometry. TOPSAR data can be collected day or night under any weather conditions, thereby avoiding the problems associated with the derivation of DEM's from air photographs that may often contain clouds. Here we describe some of our initial work on volcanoes using TOPSAR data for Mt. Hekla (Iceland) and Vesuvius (Italy). We also outline various TOPSAR topographic studies of volcanoes in the Galapagos and Hawaii that will be conducted in the near future, describe how TOPSAR complements the volcanology investigations to be conducted with orbital radars (SIR-C/X-SAR, JERS-1 and ERS-1), and place these studies into the broader context of NASA's Global Change Program

Hazard assessment at Mount Etna using a hybrid lava flow inundation model and satellite-based land classification

International audienceUsing a lava flow emplacement model and a satellite-based land cover classification, we produce a map to allow assessment of the type and quantity of natural, agricultural and urban land cover at risk from lava flow invasion. The first step is to produce lava effusion rate contours, i.e., lines linking distances down a volcano’s flank that a lava flow will likely extend if fed at a given effusion rate from a predetermined vent zone. This involves first identifying a vent mask and then running a downhill flow path model from the edge of every pixel around the vent mask perimeter to the edge of the DEM. To do this, we run a stochastic model whereby the flow path is projected 1,000 times from every pixel around the vent mask perimeter with random noise being added to the DEM with each run so that a slightly different flow path is generated with each run. The FLOWGO lava flow model is then run down each path, at a series of effusion rates, to determine likely run-out distance for channel-fed flow extending down each path. These results are used to plot effusion rate contours. Finally, effusion rate contours are projected onto a land classification map (produced from an ASTER image of Etna) to assess the type and amount of each land cover class falling within each contour. The resulting maps are designed to provide a quick look-up capability to assess the type of land at risk from lava extending from any location at a range of likely effusion rates. For our first (2,000 m) vent zone case used for Etna, we find a total of area of ~680 km2 is at risk from flows fed at 40 m3 s−1, of which ~6 km2 is urban, ~150 km2 is agriculture and ~270 km2 is grass/woodland. The model can also be run for specific cases, where we find that Etna’s 1669 vent location, if active today, would likely inundate almost 11 km2 of urban land, as well as 15.6 km2 of agricultural land, including 9.5 km2 of olive groves and 5.2 km2 of vineyards and fruit/nut orchards

Measuring SO2 Emission Rates at Kīlauea Volcano, Hawaii, Using an Array of Upward-Looking UV Spectrometers, 2014–2017

Retrieving accurate volcanic sulfur dioxide (SO2) gas emission rates is important for a variety of purposes. It is an indicator of shallow subsurface magma, and thus may signal impending eruption or unrest. SO2 emission rates are significant for accurately assessing climate impact, and providing context for assessing environmental, agricultural, and human health effects during volcanic eruptions. The U.S. Geological Survey Hawaiian Volcano Observatory uses an array of ten fixed, upward-looking ultraviolet spectrometer systems to measure SO2 emission rates at 10-s sample intervals from the Kīlauea summit. We present Kīlauea SO2 emission rates from the volcano’s summit and middle East Rift Zone during 2014–2017 and discuss the major sources of error for these measurements. Due to the wide range of SO2 emissions encountered at the summit vent, we used a variable wavelength spectral analysis range to accurately quantify both high and low SO2 column densities. We compare measured emission rates from the fixed spectrometer array to independent road and helicopter-based traverse measurements and evaluate the magnitudes and sources of uncertainties for each method. To address the challenge of obtaining accurate plume speed measurements, we examine ground-based wind-speed, plume speed tracking via spectrometer, and SO2 camera derived plume speeds. Our analysis shows that: (1) the summit array column densities calculated using a dual fit window, are within -6 to +22% of results obtained with a variety of other conventional and experimental retrieval methods; (2) emission rates calculated from the summit array located ∼3 km downwind provide the best, practical estimate of summit SO2 release under normal trade wind conditions; (3) ground-based anemometer wind speeds are 22% less than plume speeds determined by cross-correlation of plume features; (4) our best estimate of average Kīlauea SO2 release for 2014–2017 is 5100 t/d, which is comparable to the space-based OMI emissions of 5518 t/d; and (5) short-term variability of SO2 emissions reflects Kīlauea lava lake dynamics

Monitoring the evolution of the Pasig–Potrero alluvial fan, Pinatubo Volcano, using a decade of remote sensing data

Since the 1991 climactic eruption of Pinatubo in the Philippines, various hazards have affected areas surrounding the volcano. The most significant of these hazards involve the redeposition of pyroclastic flow and fall deposits as lahars, deposit-derived pyroclastic flows, and ash falls due to phreatic explosions. Many of these processes occurred in areas that are inaccessible for ground observation and monitoring. We describe here how sequential remote sensing data obtained over the period December 18, 1991, to November 1, 2001, from the SPOT, ERS, RADARSAT, SIR-C/X-SAR, AIRSAR, LANDSAT 7 ETM, and ASTER sensors provide a means of monitoring the decade-long development of the post-eruption Pinatubo landscape. This method represents an efficient and safe alternative to time-consuming, physically demanding and risky field campaigns. We apply principal component analysis, image subtraction, band ratioing, and density slicing to these data to track the changes in the post-eruption landscape, estimate volumes of deposition, and allow hazard vulnerability prediction along the timeline establish by the series of data sets. The maps derived from the remote sensing data agree well with the field derived maps for the first 5 years (1991–1995), provide important large-area coverage, and show details that are unobtainable from conventional ground-based mapping. The volume of lahars deposited during the first 6 months following the eruption is estimated between 0.045 and 0.075 km3, covering an area of 45 km2. Moreover, changes in the settlement patterns of the local population, as well as in the construction and modification of the engineering structures for controlling the lahar hazards, can be identified in the multi-temporal scenes spanning the entire decade of observations. These types of information are crucial inputs for local decision- and policy-making in volcanic hazard mitigation

Fissure eruptions in Tharsis, Mars : implications for eruption conditions and magma sources.

The Tharsis region has been the focus of many studies of volcanism on Mars. Not only are the largest volcanoes on the planet located here, but also many of the youngest volcanic features are found within Tharsis. Comparatively little attention has been given to understanding the origin of the smaller volcanoes within Tharsis, and these smaller structures may provide important information on both the regional tectonics of the area, and the availability of magma from the shallow or deep crust. We have identified six separate, but physically close, vent systems in eastern Tharsis just to the east of the volcano Jovis Tholus. These vents are typically linear fissures a few to ~ 20 km in length that have built small shields rising to ~ 50–85 m above the level of the surrounding topography. The maximum length of individual lava flows from these fissures is ~ 30 km, but more typical lengths are 15–20 km. Mapping of the vent complexes reveals that smooth material, interpreted to be spatter from fire fountaining, is located on the rims of some of the fissures. This spatter then formed either short (< 5 km) flows or merged close to the fissure to form the longer flows. There appears to have been some temporal evolution of the flow field, as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows. We find evidence of frozen lava ponds and channelized flows from central vents. Photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute, originally identified by Mouginis-Mark and Christensen [Mouginis-Mark, P.J., Christensen, P.R., 2005. New observations of volcanic features on Mars from the THEMIS instrument. J. Geophys. Res. 110: E8, doi: 10.1029/2005JE002421], of the flows from the central vent complex: they are all < 5 m thick, which is a factor of ~ 8–15 thinner than flows elsewhere on Mars. To investigate the unusual eruption conditions (limited total volume of the construct and of individual flows) we model the lava rheology, the duration of emplacement, the subsurface conditions that may have led to these eruptions, and the volatile content of the magma. We find lava viscosities and yield strengths to be ~ 100 Pa s and ~ 100 Pa, respectively, eruption rates to be ~ 5000 m3 s− 1, flow speeds to be 1–2 m s− 1, durations of emplacement of individual flow units to be ~ 5 h, and the equivalent magma water content to be 0.1–0.2 mass%. These eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions. Small vents such as the ones studied here have also been identified in other parts of eastern Tharsis, so that the eruptions described here may characterize a common style of volcanism on Mars that can only be identified now that image spatial resolution in the range 1–20 m/pixel is available. It is therefore possible that additional searches of other volcanic areas (Syrtis Planum, Elysium Planitia, and Hesperia Planum) may also show greater diversity of activity than is currently accepted

Investigation of at-vent dynamics and dilution using thermal infrared radiometers at Masaya volcano, Nicaragua

In order to develop a detailed understanding of the dynamics of gas puffing (gas release as a series of distinct pulses) and more sustained degassing (steady plumes of gas) during persistent volcanic degassing, measurements of gas mass flux are required in the vicinity of the volcanic vent. Masaya volcano (Nicaragua), a persistently degassing system, is an ideal location for measuring the dynamics of releases of volcanic gas in the first few seconds of their propagation. We carried out two field experiments during February 2002 and March 2003, during which thermal infrared thermometers were targeted into the degassing vent at Masaya to record thermal variations related to variations in the at-vent gas emission over short (on the order of seconds) time scales. The thermometers recorded an oscillating signal as gas puffs passed through the field of view, detailing variations in the degassing process developing over time scales of seconds. These data were processed to extract puff frequencies, amplitudes, durations, emission velocities and volumes. These data showed that, over time periods of hours, the total gas flux was stable with little variation in the puffing frequency. However, between the 2002 and 2003 data set we noted an increase in mean plume temperature, puffing frequency, puff emission velocity and puff volume, as well as a decrease in mean puff duration. These changes were consistent with a thermal data-derived increase in emitted gas flux from 4.2 × 107 m3 d- 1 to 6.4 × 107 m3 d- 1 between the two campaigns. Turbulent gas puffs entrain surrounding air, and quantifying the magnitude of air entrainment, or dilution, represents a major challenge for the measurement of total volcanic gas emissions. Our observations of small gas puffs suggest that they behave as turbulent buoyant thermals, and we use equations for mass, momentum and buoyancy, coupled with the standard entrainment assumption for turbulent buoyant flows, to estimate the gas puff dilution. The theoretically calculated dilution of 0.09 and 0.24 between emission and detection yields total SO2 mass fluxes of 209 t d- 1 and 864 t d- 1 for 2002 and 2003, respectively. This compares well with UV-spectrometer SO2 fluxes of 470 and 680 t d- 1 for February 2002 and March 2003, respectively. © 2007 Elsevier B.V. All rights reserved

First recorded eruption of Mount Belinda volcano (Montagu Island), South Sandwich Islands

The MODVOLC satellite monitoring system has revealed the first recorded eruption of Mount Belinda volcano, on Montagu Island in the remote South Sandwich Islands. Here we present some initial qualitative observations gleaned from a collection of satellite imagery covering the eruption, including MODIS, Landsat 7 ETM+, ASTER, and RADARSAT-1 data. MODVOLC thermal alerts indicate that the eruption started sometime between 12 September and 20 October 2001, with low-intensity subaerial explosive activity from the islandrsquos summit peak, Mount Belinda. By January 2002 a small lava flow had been emplaced near the summit, and activity subsequently increased to some of the highest observed levels in August 2002. Observations from passing ships in February and March 2003 provided the first visual confirmation of the eruption. ASTER images obtained in August 2003 show that the eruption at Mount Belinda entered a new phase around this time, with fresh lava effusion into the surrounding icefield. MODIS radiance trends also suggest that the overall activity level increased significantly after July 2003. Thermal anomalies continued to be observed in MODIS imagery in early 2004, indicating a prolonged low-intensity eruption and the likely establishment of a persistent summit lava lake, similar to that observed on neighboring Saunders Island in 2001. Our new observations also indicate that lava lake activity continues on Saunders Island

Downstream aggradation owing to lava dome extrusion and rainfall runoff at Volcán Santiaguito, Guatemala

Persistent lava extrusion at the Santiaguito dome complex (Guatemala) results in continuous lahar activity and river bed aggradation downstream of the volcano. We present a simple method that uses vegetation indices extracted from Landsat Thematic Mapper (TM) data to map impacted zones. Application of this technique to a time series of 21 TM images acquired between 1987 and 2000 allow us to map, measure, and track temporal and spatial variations in the area of lahar impact and river aggradation. In the proximal zone of the fluvial system, these data show a positive correlation between extrusion rate at Santiaguito (E), aggradation area 12 months later (Aprox), and rainfall during the intervening 12 months (Rain12): Aprox = 3.92 + 0.50 E + 0.31 ln(Rain12) (r2= 0.79). This describes a situation in which an increase in sediment supply (extrusion rate) and/or a means to mobilize this sediment (rainfall) results in an increase in lahar activity (aggraded area). Across the medial zone, we find a positive correlation between extrusion rate and/or area of proximal aggradation and medial aggradation area (Amed): Amed = 18.84 - 0.05 Aprox - 6.15 Rain12 (r2 = 0.85). Here the correlation between rainfall and aggradation area is negative. This describes a situation in which increased sediment supply results in an increase in lahar activity but, because it is the zone of transport, an increase in rainfall serves to increase the transport efficiency of rivers flowing through this zone. Thus, increased rainfall flushes the medial zone of sediment. These quantitative data allow us to empirically define the links between sediment supply and mobilization in this fluvial system and to derive predictive relationships that use rainfall and extrusion rates to estimate aggradation area 12 months hence

Volumetric characteristics of lava flows from interferometric radar and multispectral data: the 1995 Fernandina and 1998 Cerro Azul eruptions in the western Galápagos.

We have used a suite of remotely sensed data, numerical lava flow modeling, and field observations to determine quantitative characteristics of the 1995 Fernandina and 1998 Cerro Azul eruptions in the western Galápagos Islands. Flank lava flow areas, volumes, instantaneous effusion rates, and average effusion rates were all determined for these two eruptions, for which only limited syn-eruptive field observations are available. Using data from SPOT, TOPSAR, ERS-1, and ERS-2, we determined that the 1995 Fernandina flow covers a subaerial area of 6.5×10 6 m 2 and has a subaerial dense rock equivalent (DRE) volume of 42×10 6 m 3. Field observations, ATSR satellite data, and the FLOWGO numerical model allow us to determine that the effusion rate declined exponentially from a high of ~60–200 m 3 s -1 during the first few hours to <5 m 3 s -1 prior to ceasing after 73 days, with a mean effusion rate of 4–16 m 3 s -1. Integrating the ATSR-derived, exponentially declining effusion rate over the eruption duration produces a total (subaerial + submarine) DRE volume of between 27 and 100×10 6 m 3, the range in values being due to differing assumptions about heat loss characteristics; only values in the higher part of this range are consistent with the independently derived subaerial volume. Using SPOT, TOPSAR, ERS-1, and ERS-2 data, we determine that the 1998 Cerro Azul flow is 16 km long, covers 16 km 2, and has a DRE volume of 54×10 6 m 3. FLOWGO produces at-vent velocity and effusion rate values of 11 m s -1 and ~600 m 3 s -1, respectively. The velocity value agrees well with the 12 m s -1 estimated in the field. The mean effusion rate (total DRE volume/duration) was 7–47 m 3 s -1. Dike dimensions, fissure lengths, and pressure gradients along the conduit based on magma chamber depth estimates of 3–5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude, the range being due to uncertainty in the magma viscosity, dike dimensions, and pressure gradient between magma chamber and vent. Although somewhat consistent with mean effusion rates from other techniques, their wide range makes them less useful. The exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions. Our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption, as well as time constants of exponential decay during the eruption. The results and theoretical relationships combine to indicate that at both volcanoes probably 25–30% of the volumetric increase in the magma chamber erupted as lava onto the surface. In both eruptions the lava flow volumes are less than 1% of the magma chamber volume

Accurately measuring volcanic plume velocity with multiple UV spectrometers

Abstract A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least two timesynchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the time varying structure of SO 2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s −1 . Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements