Ground truth spectrometry and imagery of eruption clouds to maximize utility of satellite imagery

Field experiments with thermal imaging infrared radiometers were performed and a laboratory system was designed for controlled study of simulated ash clouds. Using AVHRR (Advanced Very High Resolution Radiometer) thermal infrared bands 4 and 5, a radiative transfer method was developed to retrieve particle sizes, optical depth and particle mass involcanic clouds. A model was developed for measuring the same parameters using TIMS (Thermal Infrared Multispectral Scanner), MODIS (Moderate Resolution Imaging Spectrometer), and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer). Related publications are attached

Retrieval of sizes and total masses of particles in volcanic clouds using AVHRR bands 4 and 5

The advanced very high resolution radiometer (AVHRR) sensor on polar orbiting NOAA satellites can discriminate between volcanic clouds and meteorological clouds using two-band data in the thermal infrared. This paper is aimed at developing a retrieval of the particle sizes, optical depth, and total masses of particles from AVHRR two-band data of volcanic clouds. Radiative transfer calculations are used with a semi-transparent cloud model that is based on assumptions of spherical particle shape, a homogeneous underlying surface, and a simple thin cloud parallel to the surface. The model is applied to observed AVHRR data from a 13-hour old drifting cloud from the August 19, 1992, eruption of Crater Peak/Spurr Volcano, Alaska. The AVHRR data fit in the range of results calculated by the model, which supports its credibility. According to the model results, the average of effective particle radius in the test frame of this cloud is in the range of 2 to 2.5 μm, the optical depth at 12 μm is about 0.60–0.65. The total estimated mass of ash in the air amounts to 0.24–0.31×106 tons, which is about 0.7–0.9% of the mass measured in the ashfall blanket. Sensitivity tests show that the mass estimate is more sensitive to the assumed ash size distribution than it is to the ash composition

GOES imagery fills gaps in Montserrat volcanic cloud observations

GOES satellite imagery offers great potential to lessen the risk of volcanic ash clouds to aviation, and the situation at Montserrat in the Caribbean is providing the proof. Many transatlantic, commercial, and private aircraft use airspace around Montserrat, where the Soufriere Hills Volcano has been erupting since 1995. Worldwide over the last 15 years, more than 80 airplanes have reported encountering volcanic ash along flight paths. Encounters cannot be avoided because onboard radar cannot detect fine-grained ash particles—those with a radius of 15 microns or less. In recent years volcanic cloud encounters are estimated to have caused hundreds of millions of dollars worth of damage and in a few cases have caused in-flight engine failure [Casadevall et al., 1996]

Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using weather radar

Observations of the March 19, 1982 ash eruption of Mount St. Helens, made by the National Weather Service (NWS, Portland, Oregon) on 5-cm radar, were used to estimate the volume of the ash cloud (2000 ±500 km3), the concentration of ash (0.2–0.6 g m−3). and the total mass of ash erupted (3–10×1011 g). The position of the cloud was also tracked by radar. Particle sizes in the ash cloud were estimated from settling velocities suggested by decreases in maximum ash cloud height with time as it moved away from the volcano. The March 19, 1982 ash blanket was sampled and mapped. Ash fallout times and accumulation rates were reconstructed from ground observations. Grain size distributions for various samples were used to obtain particle concentration (0.2 g m−3), total ashfall mass (1–3×1011 g), and radar reflectivity factor (4–5 mm6 m−3) for the ash cloud. Our preferred estimate for total ashfall mass (4×1011 g) is that obtained from the product of the ash cloud volume determined by radar (2000±500 km3) and the particle concentration inferred from ashfall data (0.2 g m−3). Previously published ashfall data for the May 18, 1980 Mount St. Helens eruption has been studied using our ashfall inversion technique to estimate 6-hour mean particle concentration (3 g m−3), the size distribution, total ashfall mass (5×1014 g), and radar reflectivity factors (7–60 mm6 m−3) for the ash cloud. A somewhat higher value (9 g m−3) for particle concentration was estimated from radar observations [Harris et al., 1981] for an ash cloud formed during the peak eruption rate at Mount St. Helens. The two independent estimates are consistent, given the many uncertainties of the problem. The reflectivity factors for very dense ash clouds (3–9 g m−3) are several orders of magnitude smaller than for severe weather considered routinely detectable by airborne weather radar and dangerous for aviation. Because volcanic ash clouds with particle concentrations of at least 0.2 g m−3 are produced in extremely small eruptions (in terms of total ashfall mass) of duration less than 1 minute, volcanic ash clouds must be considered an extremely serious hazard to in-flight aircraft, regardless of eruption magnitude. These factors should be considered in hazard evaluations for known volcanoes located near air routes. Radar observations and calculations can provide scientists monitoring eruptive activity with significant information for estimating duration of eruption, particle concentrations in ash clouds, total mass of solid material erupted, magma eruption rate, potential ashfall mass, ashfall locations and accumulation rates, and duration and amounts of ashfall. Detailed analysis of ashfall data and NWS radar observations of ash clouds from Mount St. Helens demonstrate that weather radar can yield such timely information during and following volcanic eruptions

The 1966 eruption of Izalco Volcano, El Salvador

During October–November 1966 900,000 m3 of olivine basalt flowed from the flank of Izalco volcano, El Salvador. The total heat energy was approximately 1015 calories. No measurable changes in gravity occurred at stations on the active cone between August 1964 and August 1967. In the summit crater fumaroles have surface temperatures as high as 540°C. The cooling rate of these fumaroles was 18°C/yr before the eruption and 45°C/yr after. Yearly temperature cycles due to wet and dry seasons are superimposed on the general cooling trend. The rate of gas emission at four fumaroles in November 1967 was 86 g/sec. The data from fumaroles and the volume of the flank eruption indicate that the volume of the high-level magma storage beneath the crater was 3.8×106 metric tons before the eruption and 1.4×106 metric tons after. Four of the larger hot fumaroles contribute at least 10% of the heat loss from the high-level magma storage, whereas heat conduction accounts for more than half the total loss

Amatitlan, An actively resurging cauldron 10 km south of Guatemala City

A 14×16 km diameter collapse caldera has been recognized 10 km south of Guatemala City, Guatemala. The caldera is north of the presently active volcano Pacaya and west of Agua, a large stratovolcano. The caldera was not previously recognized because its eastern and western margins coincide with faults that outline the Guatemala City graben and because the northern margin of the caldera is buried by pyroclastic rocks. The existence of the northern caldera margin is now established by gravity data and a variety of geological observations including circumferential faults, hot springs, well-log data, and lithological changes in sedimentary rocks. A sequence of nine silicic pyroclastic deposits, totaling a volume of more than 70 km 3 dense rock were erupted from the caldera. The ages of these eruptions are mainly between about 300,000 years B.P. to less than 23,000 years B.P. The rocks erupted at the caldera and its associated vents consist of domes and nonwelded pyroclastic flow, surge, and fall deposits, mainly of rhyolitic to dacitic composition. Successive pyroclastic eruptions have generally become smaller in volume and more silicic with time. Major and minor element chemistry distinguish Amatitlan pyroclastics from those of other nearby calderas. The caldera lies at the intersection of an offset of the volcanic chain (the Palin Shear) and the faults along the volcanic front (Jalpatagua fault zone). The caldera has a heavily faulted resurgent dome crosscut by an impressive longitudinal graben. The graben\u27s alignment with the Jalpatagua fault zone suggests a genetic relationship. The longitudinal graben and resurgent dome are morphologically youthful and are the sites of many young silicic vents. Available seismic data show a heavy concentration of epicenters over the northern part of the resurgent dome, near a young silicic intrusion. The caldera is active and will probably erupt again. Over 1 million people live within 20 km and would be threatened in the event of a moderate eruption. Suggestions for future research focus on hazard assessment and forecastin

La Yeguada volcanic vomplex in the Republic of Panama: An assessment of the geologic hazards using 40Ar/39Ar geochronology

La Yeguada volcanic complex is one of three Quaternary volcanic centers in Panama. To assess potential geologic hazards, new samples were analyzed using argon analysis (40Ar/39Ar), and obtained the following: the most recent eruption occurred approximately 32,000 years ago at the Media Luna cinder cone; the youngest dated eruption from the main dome complex occurred 357 ± 19 ka, producing the Castillo dome unit; Cerro Picacho, a separate dacite dome 1.5 km east of the main complex is 4.47 ± 0.23 Ma; and the El Satro Pyroclastic Flow unit surrounds the northern portion of the volcanic complex is 11.26 ± 0.17 Ma. No Holocene (10,000 years ago to present) activity is recorded at the La Yeguada volcanic complex and therefore, it is unlikely to produce another eruption. The main geologic hazard at the La Yeguada volcanic complex is from landslides coming off the many steep slopes

Determination of the total grain size distribution in a Vulcanian eruption column, and its implications to stratospheric aerosol perturbation

Grain size analysis of samples representing all sampleable portions of the airfall deposit produced by the Fuego volcano in Guatemala on 14 October 1974 form the basis for estimating the total grain size distribution of tephra from this eruption. The region enclosed by each isopach has a particular average grain size distribution which can be weighted proportionally to its percentage volume. The grain size of pyroclastic avalanche deposits produced during the eruption are also included. The total grain size distribution calculated as a sum of weighted distributions has a median grain size of 0.8∅ (0.6mm) and a sorting coefficient (σ∅) of 2.3. The size distribution seems to approximate Rosin and Rammler\u27s law of crushing and this observation allows us to estimate that no more than 15% volume of the fine tail of the total size distribution is likely to be missing. The ash composed of these fine particles did not fall in the region of the volcano as part of the recognizable tephra blanket. The eruption column reached well into the stratosphere: heights estimated from the ground were 10-12 km above sea level but estimated heights based on mass flux rates are higher (18-23 km). The proportion of ash smaller than 2 µm, which could remain for substantial periods in the stratosphere, is no more than 0.8% volume of the total. It seems probable that acid aerosol particles from vulcanian type eruptions are more important to stratospheric aerosol perturbation than fine silicate ash particles by at least an order of magnitude

Retrieval of mass and sizes of particles in sandstorms using two MODIS IR bands: A case study of april 7 2001 sandstorm in China

A thermal infrared remote sensing retrieval method developed by Wen and Rose [1994], which retrieves particle sizes, optical depth, and total masses of silicate particles in the volcanic cloud, was applied to an April 07, 2001 sandstorm over northern China, using MODIS. Results indicate that the area of the dust cloud observed was 1.34 million km2, the mean particle radius of the dust was 1.44 μm, and the mean optical depth at 11 μm was 0.79. The mean burden of dust was approximately 4.8 tons/km2 and the main portion of the dust storm on April 07, 2001 contained 6.5 million tons of dust. The results are supported by both independent remote sensing data (TOMS) and in-situ data for a similar event in 1998. This paper demonstrates that Wen and Rose’s retrieval method could be successfully applied to past and future sandstorm events using IR channels of AVHRR, GOES or MODIS

Sizes and shapes of 10-Ma Distal fall pyroclasts in the Ogallala gGroup, Nebraska

Size distributions of distal ashfall particles from correlated 10-Ma layers in Nebraska, measured using laser diffraction methods, are lognormal with mode diameters of ∼90 mm. This ashfall is ∼100% bubble-wall shards of rhyolite glass and apparently represents a distal ashfall from an eruption 1400 km away. Measured terminal velocities of these ash particles are 0.2–18 cm/s, consistent with Stokes Law settling of spherical particles with diameters of 9–50 mm. Surface area of the ash particles, measured with gas adsorption, is 20–30 times the surface area of equivalent Stokes spheres. These results highlight the effects of shape and atmospheric drag in distal ashfalls. They also highlight atmospheric transport and fallout of distal ashfall particles, because these deposits resemble many other ashfalls preserved in the Great Plains of North America throughout the Tertiary and Quaternary. Because the ashfalls preserve major mammalian death assemblages, they demonstrate that deposits with modes of optical diameters 1100 mm are still hazardous by aerodynamic definitions of lung disease risk and include particles substantially within hazardous PM10 ranges. The aerodynamically fine particle size may lead to substantial aeolian redistribution, causing local thicknesses of 12 m. Overall, the ashfall thicknesses observed are at least several times larger than would be expected based on exponential thinning from the volcano. Shape measurements of distal ash particles may be necessary to assess risk. The possible health risks in the central United States from a future rhyolitic eruption in the western United States may be significant