Ash Blanket Research Articles

Sustainable humanitarian engineering in practice – the East Bali Poverty Project

The paper describes the humanitarian engineering interventions made by the East Bali Poverty Project (EBPP), a private charity founded and managed by a British civil engineer in 1998 in Desa Ban, an impoverished area on the northeast slopes of Mount Agung, Bali. The abject poverty of the area – which had no access to the outside world, no schools, no clinics, no sanitation and no rivers or water supply – stemmed in part from the cataclysmic eruptions of Mount Agung in 1963, when a blanket of ash, sand and gravel was deposited over much of the area, ruining an already poor and fragile landscape. The first 10 years of EBPP's targeted interventions, chosen by the local people – improving health and education for their children – were the first priorities and were presented in previous Institution of Civil Engineers Proceedings. This paper examines the many humanitarian engineering elements that have been adopted and carried out in a sustainable manner in a very culturally sensitive and challenging physical environment over a 17-year period.

Acute sedimentation response to rainfall following the explosive phase of the 2008–2009 eruption of Chaitén volcano, Chile

The 10-day explosive phase at the start of the 2008–2009 eruption of Chaitén volcano in southern Chile (42.83°S, 72.65°W) blanketed the steep, rain-forest-cloaked, 77-km2 Chaitén River drainage basin with 3 to >100 cm of tephra; predominantly fine to extremely fine rhyolitic ash fell during the latter half of the explosive phase. Rain falling on this ash blanket within days of cessation of major explosive activity generated a hyperconcentrated-flow lahar, followed closely by a complex, multi-day, muddy flood (streamflow bordering on dilute hyperconcentrated flow). Sediment mobilized in this lahar-flood event filled the Chaitén River channel with up to 7 m of sediment, buried the town of Chaitén (10 km downstream of the volcano) in up to 3 m of sediment, and caused the lower 3 km of the channel to avulse through the town. Although neither the nature nor rate of the sedimentation response is unprecedented, they are unusual in several ways: (1) Nearly 70 percent of the aggradation (almost 5 m) in the 50–70-m-wide Chaitén River channel was caused by a lahar, triggered by an estimated 20 mm of rainfall over a span of about 24 h. An additional 2 m of aggradation occurred in the next 24–36 h. (2) Direct damage to the town was accomplished by the sediment-laden water-flood phase of the lahar-flood event, not the lahar phase. (3) The volume of sediment eroded from hillslopes and delivered to the Chaitén River channel was at least 3–8 × 106 m3—roughly 15–40 % of the minimum tephra volume that mantled the Chaitén River drainage basin. (4) The acute sedimentation response to rainfall appears to have been due to the thickness and fineness of the ash blanket (inhibiting infiltration of rain) and the steepness of the basin’s hillslopes. Other possible factors such as the prior formation of an ash crust, development of a hydrophobic surface layer, or large-scale destruction of rain-intercepting vegetation did not play a role.

The climatic impact of supervolcanic ash blankets

Supervolcanoes are large caldera systems that can expel vast quantities of ash, volcanic gases in a single eruption, far larger than any recorded in recent history. These super-eruptions have been suggested as possible catalysts for long-term climate change and may be responsible for bottlenecks in human and animal populations. Here, we consider the previously neglected climatic effects of a continent-sized ash deposit with a high albedo and show that a decadal climate forcing is expected. We use a coupled atmosphere-ocean General Circulation Model (GCM) to simulate the effect of an ash blanket from Yellowstone volcano, USA, covering much of North America. Reflectivity measurements of dry volcanic ash show albedo values as high as snow, implying that the effects of an ash blanket would be severe. The modeling results indicate major disturbances to the climate, particularly to oscillatory patterns such as the El Nino Southern Oscillation (ENSO). Atmospheric disruptions would continue for decades after the eruption due to extended ash blanket longevity. The climatic response to an ash blanket is not significant enough to instigate a change to stadial periods at present day boundary conditions, though this is one of several impacts associated with a super-eruption which may induce long-term climatic change.

Early evolution of a stratospheric volcanic eruption cloud as observed with TOMS and AVHRR

This paper is a detailed study of remote sensing data from the total ozone mapping spectrometer (TOMS) and the advanced very high resolution radiometer (AVHRR) satellite detectors, of the 1982 eruption of El Chichón, Mexico. The volcanic cloud/atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud [Krueger et al., 1995] with thermal infrared retrievals of the size, optical depth, and mass of fine‐grained (1–10 μm radius) volcanic ash [Wen and Rose, 1994]. Our study provides the first direct evidence of gravitational separation of ash from a stratospheric, gas‐rich, plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds. The eruption column reached as high as 32 km [Carey and Sigurdsson, 1986] and was injected into an atmosphere with a strong wind shear, which allowed for an observation of the separation of sulfur dioxide and volcanic ash. The upper, more sulfur dioxide‐rich part of the cloud was transported to the west in the stratosphere, while the fine‐grained ash traveled to the south in the troposphere. The mass of sulfur dioxide released was estimated at 7.1 × 109 kg with the mass decreasing by approximately 4% 1 day after the peak. The mass of fine‐grained volcanic ash detected was estimated at 6.5 × 109 kg, amounting to about 0.7% of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano. Over the following days, 98% of this remaining fine ash was removed from the volcanic cloud, and the effective radius of ash in the volcanic cloud decreased from about 8 μm to about 4 μm.

An analytically based model for the simultaneous leaching-chain decay of radionuclides from contaminated ground surface soil layers.

This paper describes an analytically based method for modeling the time-dependent radionuclide areal densities of contaminated soil surface layers when the soil experiences simultaneous leaching, surface erosion and chain radioactive decay. The model is used to predict time-dependent radionuclide areal densities in a volcanic ash blanket contaminated with spent nuclear fuel particles for the purpose of assessing the risks of radiation exposure from an extrusive volcanic event near a proposed high-level waste repository at Yucca Mountain. The method uses general analytical solutions (an expansion of the Bateman equations) for calculating serial decay, including non-radioactive decay loss terms, in order to calculate time-dependent radionuclide areal densities in the ash blanket. In the presented example, 43 "key" radionuclides are tracked and their concentrations in the blanket are displayed for a 10,000-y time period following the volcanic event. Although the analysis presented herein is for modeling contaminated volcanic ash blankets, the model would work equally well for modeling time-dependent radionuclide contamination of land surfaces in, for example, site decommissioning. It is suggested that the general solutions for serial decay (with non-radioactive decay loss terms) can also be used to model the release of radionuclides from the waste packages under anticipated repository conditions.

Worldwide dispersal of ash and gases from earth's largest known eruption: Toba, Sumatra, 75 ka

The eruption of the Youngest Toba Tuff (YTT) occurred 75 ± 2 ka in North Sumatra (2°45′N, 98°45′E). The eruption produced at least 2800 km 3 of dense rock equivalent (DRE) rhyolite magma (7 × 10 18 g). Much of the volume of magma was preserved as a non-welded outflow sheet covering 20,000–30,000 km 2 and a thick, welded intracaldera tuff. At least 800 km 3 (2 × 10 18 g) of Toba ash was deposited in an extensive ash blanket over the Indian Ocean and Southern Asia. Detailed studies of the chemistry of minerals and glasses in pumices from the YTT enable estimation of the minimum masses of gaseous components released to earth's atmosphere during the eruption: H 2O:. The high eruption rate, with the entire event lasting perhaps 9–14 days make stratospheric venting of a significant fraction of these gases and associated silicate ash and aerosol particles likely. The masses of ash and gases released is nearly two orders of magnitude higher than any known historic eruption.

Worldwide dispersal of ash and gases from earth's largest known eruption: Toba, Sumatra, 75 ka

The eruption of the Youngest Toba Tuff (YTT) occurred 75 ± 2 ka in North Sumatra (2°45′N, 98°45′E). The eruption produced at least 2800 km 3 of dense rock equivalent (DRE) rhyolite magma (7 × 10 18 g). Much of the volume of magma was preserved as a non-welded outflow sheet covering 20,000–30,000 km 2 and a thick, welded intracaldera tuff. At least 800 km 3 (2 × 10 18 g) of Toba ash was deposited in an extensive ash blanket over the Indian Ocean and Southern Asia. Detailed studies of the chemistry of minerals and glasses in pumices from the YTT enable estimation of the minimum masses of gaseous components released to earth's atmosphere during the eruption: H 2O:. The high eruption rate, with the entire event lasting perhaps 9–14 days make stratospheric venting of a significant fraction of these gases and associated silicate ash and aerosol particles likely. The masses of ash and gases released is nearly two orders of magnitude higher than any known historic eruption.

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.

Sedimentology of Volcaniclastic Deposits from 1971-1974 Eruption Cluster of Volcano Fuego, Guatemala: ABSTRACT

Volcaniclastic sedimentation during and subsequent to the 1971-74 eruption cluster of the Volcano Fuego in Guatemala has occurred in four distinct phases which are part of a 15 to 25 year cycle of sedimentation. In phase 1, the eruption cluster generated 6 × 108 cu m of tephra, one-third in the form of glowing avalanches, the remainder as an elongate airfall ash blanket west-southwest of the cone. Glowing avalanches with a volume of 5 × 107 cu m formed two fans, each 1 to 3 m thick, east and west of the crater. Further avalanches flowed down seven narrow canyons radiating to the south of the crater forming 40-m-thick deposits totaling 1.3 × 108 cu m. During phase 2, debris flows and flash floods removed about one-third of th phase 1 canyon deposits in the first 2 years following eruption. Fan deposits remained intact. Three digitate, 1 to 2.5-m-thick, debris-flow deposits (2.2 × 107 cu m) and two 1-m-thick flood fans (1.8 × 107 cu m) formed south of the crater. In phase 3, terraced, meandering, suspended-load streams were metamorphosed to braided, aggrading, bed-load systems annually eroding 6 million tons of phase 1 and 2 debris, primarily from the canyon deposits. Transport of about two-thirds of this debris to the sea has produced rapid coastal progradation. During phase 4, 15 to 25 years of phase 1 and 2 activity will remove canyon avalanche deposits, redistributing the material in stable fans on the lower volcanic slopes. Phase 1 and 2 processes become inactive while str am incision produces discontinuous terracing. Fluvial systems return to meandering, suspended-load streams. End_of_Article - Last_Page 843------------

The September 28–30, 1965 eruption of Taal Volcano, Philippines

A moderately violent phreatomagmatic explosive eruption of Taal Volcano, Philippines, occurred from 28 to 30 September, 1965. The main phreatic explosions, which were preceded by ejection of basaltic spatter, opened a new crater 1.5 km long and 0.3 km wide on the southwest side of Volcano Island in Lake Taal. The eruption covered an area of about 60 square kilometers with a blanket of ash more than 25 cm thick and killed approximately 200 persons. The clouds that formed during the explosive eruption rose to heights of 15 to 20 km and deposited fine ash as far as 80 km west of the vent. At the base of the main explosion column, flat, turbulent clouds spread radially, with hurricane velocity, transporting ash, mud, lapilli and blocks. The horizontally moving, debris-laden clouds, sandblasted trees, coated the blast side of trees and houses with mud, and deposited coarse ejecta with dune-type bedding in a zone roughly 4 km in all directions from the explosion crater.

The Mt. Spurr eruption, July 9, 1953

The July 9, 1953 eruption of a subsidiary cone of Mt. Spurr, Alaska, is of particular interest because the initial phases were under close observation by the crews of two jet aircraft which were in the vicinity when the eruption started. Within one hour the eruption cloud assumed a mushroom shape which reached an altitude of approximately 70,000 ft. Extremely heavy rains accompanying the eruption, and water supplied by the melting of ice in the immediate vicinity of the vent, caused flash floods which carried sufficient debris to dam one of the major rivers in the area and form a lake nearly five miles long. A one‐quarter‐inch blanket of ash was deposited on the city of Anchorage, 80 mi from Mt. Spurr; but, in the opposite direction, no discoloration of snow fields and glaciers could be seen within two or three miles of the volcano. Observations of this eruption of Mt. Spurr particularly emphasize the importance of prevailing wind direction in the control of ash‐fall distribution resulting from an eruption of this type.