Simon A. Carn

Band residual difference algorithm for retrieval of SO/sub 2/ from the aura ozone monitoring instrument (OMI)

The Ozone Monitoring Instrument (OMI) on EOS/Aura offers unprecedented spatial and spectral resolution, coupled with global coverage, for space-based UV measurements of sulfur dioxide (SO/sub 2/). This paper describes an OMI SO/sub 2/ algorithm (the band residual difference) that uses calibrated residuals at SO/sub 2/ absorption band centers produced by the NASA operational ozone algorithm (OMTO3). By using optimum wavelengths for retrieval of SO/sub 2/, the retrieval sensitivity is improved over NASA predecessor Total Ozone Mapping Spectrometer (TOMS) by factors of 10 to 20, depending on location. The ground footprint of OMI is eight times smaller than TOMS. These factors produce two orders of magnitude improvement in the minimum detectable mass of SO/sub 2/. Thus, the diffuse boundaries of volcanic clouds can be imaged better and the clouds can be tracked longer. More significantly, the improved sensitivity now permits daily global measurement of passive volcanic degassing of SO/sub 2/ and of heavy anthropogenic SO/sub 2/ pollution to provide new information on the relative importance of these sources for climate studies.

Volcanic eruption detection by the Total Ozone Mapping Spectrometer (TOMS) instruments: a 22-year record of sulphur dioxide and ash emissions

Abstract Since their first depolyment in November 1978, the Total Ozone Mapping Spectrometer (TOMS) instruments have provided a robust and near-continuous record of sulphur dioxide (SO2) and ash emissions from active volcanoes worldwide. Data from the four TOMS satellites that have flown to date have been analysed with the latest SO2/ash algorithms and incorporated into a TOMS volcanic emissions database that presently covers 22 years of SO2 and ash emissions. The 1978–2001 record comprises 102 eruptions from 61 volcanoes, resulting in 784 days of volcanic cloud observations. Regular eruptions of Nyamuragira (DR Congo) since 1978, accompanied by copious SO2 production, have contributed material on approximately 30% of the days on which clouds were observed. The latest SO2 retrieval results from Earth Probe (EP) TOMS document a period (1996–2001) lacking large explosive eruptions, and also dominated by SO2 emission from four eruptions of Nyamuragira. EP TOMS has detected the SO2 and ash produced during 23 eruptions from 15 volcanoes to date, with volcanic clouds observed on 158 days. The EP TOMS instrument began to degrade in 2001, but has now stabilized, although its planned successor (QuikTOMS) recently failed to achieve orbit. New SO2 algorithms are currently being developed for the Ozone Monitoring Instrument, which will continue the TOMS record of UV remote sensing of volcanic emissions from 2004 onwards.

The February–March 2000 Eruption of Hekla, Iceland from a Satellite Perspective

An 80,000 km 2 stratospheric volcanic cloud formed from the 26 February 2000 eruption of Hekla (63.98° N, 19.70° W). POAM-III profiles showed the cloud was 9-12 km asl. During 3 days this cloud drifted north. Three remote sensing algorithms (TOMS SO 2 , MODIS & TOVS 7.3 μm IR and MODIS 8.6 μm IR) estimated ∼0.2 Tg SO 2 . Sulfate aerosol in the cloud was 0.003-0.008 Tg, from MODIS IR data. MODIS and AVHRR show that cloud particles were ice. The ice mass peaked at ∼1 Tg ∼10 hours after eruption onset. A ∼0.1 Tg mass of ash was detected in the early plume. Repetitive TOVS data showed a decrease of SO 2 in the cloud from 0.2 Tg to below TOVS detection (i.e.<0.01 Tg) in ∼3.5 days. The stratospheric height of the cloud may result from a large release of magmatic water vapor early (1819 UT on 26 February) leading to the ice-rich volcanic cloud. The optical depth of the cloud peaked early on 27 February and faded with time, apparently as ice fell out. A research aircraft encounter with the top of the cloud at 0514 UT on 28 February, 35 hours after eruption onset, provided validation of algorithms. The aircrafts instruments measured ∼0.5-1 ppmv SO 2 and ∼35-70 ppb sulfate aerosol in the cloud, 10-30% lower than concentrations from retrievals a few hours later. Different SO 2 algorithms illuminate environmental variables which affect the quality of results. Overall this is the most robust data set ever analyzed from the first few days of stratospheric residence of a volcanic cloud.

The Unexpected Awakening of Chaitén Volcano, Chile

On 2 May 2008, a large eruption began unexpectedly at the inconspicuous Chaiten volcano in Chile’s southern volcanic zone. Ash columns abruptly jetted from the volcano into the stratosphere, followed by lava dome effusion and continuous low- altitude ash plumes [Lara, 2009]. Apocalyptic photographs of eruption plumes suffused with lightning were circulated globally. Effects of the eruption were extensive. Floods and lahars inundated the town of Chaiten, and its 4625 residents were evacuated. Widespread ashfall and drifting ash clouds closed regional airports and cancelled hundreds of domestic flights in Argentina and Chile and numerous international flights [Guffanti et al., 2008]. Ash heavily affected the aquaculture industry in the nearby Gulf of Corcovado, curtailed ecotourism, and closed regional nature preserves. To better prepare for future eruptions, the Chilean government has boosted support for monitoring and hazard mitigation at Chaiten and at 42 other highly hazardous, active volcanoes in Chile. The Chaiten eruption discharged rhyolite magma, a high-silica composition associated with extremes of eruptive behavior ranging from gentle lava effusion to violent, gas-driven explosions. As the first major rhyolitic eruption since that of Alaska’s Katmai-Novarupta in 1912, it permits observations that are benchmarks for future such events. It also reignites the debate on what processes rekindle long-dormant volcanoes, justifies efforts to mitigate rare but significant hazards through ground-based monitoring, and confi rms the value of timely satellite observations.

Anatomy of a lava dome collapse: the 20 March 2000 event at Soufrière Hills Volcano, Montserrat

Abstract A second extrusive phase of the currently ongoing 1995–2003 eruption of Soufriere Hills Volcano (SHV), Montserrat, commenced in mid-November 1999 following ∼19 months during which no fresh lava had reached the surface. By mid-March 2000, a new andesite lava dome constructed within a collapse scar girdled by remnants of the 1995–1998 dome complex had attained an estimated volume of ∼29±3 million m3 (Mm3). On 20 March 2000, during a period of heavy rainfall on the island, a significant collapse event ensued that removed ∼95% of the new lava dome (∼28±3 Mm3) during ∼5 hours of activity that generated ∼40 pyroclastic flows and at least one magmatic explosion. The associated ash cloud reached an altitude of ∼9 km and deposited ash on the island of Guadeloupe to the southeast, and a number of lahars and debris flows occurred in valleys on the flanks of SHV. A large quantity of observational data, including contemporaneous field observations and continuous data from the broadband seismic network on Montserrat, allow a detailed reconstruction of this dome collapse event. In contrast to most of the large dome collapses at SHV, the 20 March 2000 event is distinguished by a lack of short-term precursory elevated seismicity at shallow depths beneath the lava dome. Broadband seismic amplitude data recorded during the event are used to infer the cumulative volume of collapsed dome as the collapse progressed. These data indicate that the high-velocity pyroclastic flows observed at the climax of the event removed by far the largest portion (∼68%) of the lava dome at peak discharge rates (estimated from the seismic record) of ∼2×104 m3 s−1. Following the 20 March 2000 collapse, lava dome growth recommenced immediately and continued without significant interruption until another, larger dome collapse occurred on 29 July 2001. The 29 July 2001 event also coincided with heavy rainfall on Montserrat [Matthews et al. (2002) Geophys. Res. Lett. 29; DOI:10.1029/2002GL014863] and lacked precursory elevated seismic activity. We attribute the initiation of the 20 March 2000 collapse to a prolonged spell of heavy rainfall on the lava dome prior to and during the event. The precise causal mechanism remains controversial, though some combination of mechanical erosion and/or destabilization of a critically poised face of the lava dome, the action of pressurized steam or water on potential failure surfaces within the dome, rapid cooling of hot lava and small phreatic explosions seems likely. Anecdotal evidence exists for other rainfall-induced activity on Montserrat, and the triggering of explosive or pyroclastic flow activity by rainfall has been noted at dome-forming volcanoes elsewhere, including Merapi, Indonesia [Voight et al. (2000) J. Volcanol. Geotherm. Res. 100, 69–138], Unzen, Japan [Yamasato et al. (1997) Papers Meteorol. Geophys. 48], Santiaguito, Guatemala [Smithsonian Institution Global Volcanism Network Bull. 15 (1990)] and Mount St. Helens, USA [Mastin (1994) Geol. Soc. Am. Bull. 106, 175–185]. Hazard mitigation plans at dome-forming volcanoes would therefore benefit from the inclusion of meteorological forecasting and rain monitoring equipment, particularly in the tropics.

Stratospheric Aerosol--Observations, Processes, and Impact on Climate

Interest in stratospheric aerosol and its role in climate have increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any nonvolcanically driven change, making them difficult to understand. While the role of carbonyl sulfide as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of nonsulfate matter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes.

Measuring global volcanic degassing with the Ozone Monitoring Instrument (OMI)

Abstract The ultraviolet (UV) Ozone Monitoring Instrument (OMI), launched on NASAs Aura satellite in July 2004, was the first space-based sensor to provide operational sulphur dioxide (SO2) measurements (OMSO2) for use by the scientific community. Herein, we discuss the application of OMSO2 data for the monitoring of global volcanic SO2 emissions, with an emphasis on lower tropospheric volcanic plumes. We review the algorithms used to produce OMSO2 data and highlight some key measurement sensitivity issues. The data processing scheme used to generate web-based OMSO2 data subsets for volcanic regions and estimate SO2 burdens in volcanic plumes is outlined. We describe three techniques to derive SO2 emission rates from the OMSO2 measurements, and employ one method (using single OMI pixels to estimate SO2 fluxes) to elucidate SO2 flux detection thresholds on a global scale. Applications of OMSO2 data to volcanic degassing studies are demonstrated using four case studies. These examples show how OMSO2 measurements correlate with changes in eruptive activity at Kilauea volcano (Hawaii), constrain small, potentially significant SO2 releases from reawakening, historically inactive volcanoes, track long-term changes in SO2 degassing from Nyiragongo volcano (D.R. Congo), and detect SO2 emissions from the remote Lastarria Volcano (Chile), in the actively deforming Lazufre region.

The Lamongan volcanic field, East Java, Indonesia: physical volcanology, historic activity and hazards

Abstract The Lamongan volcanic field (LVF) in East Java, Indonesia, consists of up to 61 basaltic cinder or spatter cones, a minimum of 29 prehistoric maars, and a central compound complex comprising three main vents including the historically active Lamongan volcano. The field lies on the Sunda volcanic arc and abuts onto the currently active Tengger caldera–Semeru complex to the west. Between 1799 and 1898, Lamongan was persistently active and discharged up to 15 lava flows of basaltic to basaltic andesite composition, which is probably more than what was erupted by any other Indonesian volcano in that period. Several seismic crises have been recorded in the LVF since Lamongans last eruption. There are no existing records of cinder cone or maar-forming eruptions in the area. Despite the possible hazards posed by future activity in the LVF, the history and structure of the field have been subject to little scrutiny. This contribution presents the results of a detailed morphometric and volumetric investigation of prehistoric vents and historic lava flows in the LVF, using field data, historic records, satellite imagery and modelling of erupted volumes. A typical LVF maar is characterised as a crater with a diameter of 450 m; generated by an eruption with a model ejecta volume of 0.016 km 3 dense rock equivalent (DRE) and a model juvenile component volume of 0.0096 km 3 DRE. Diameter/depth ratios of some maars display a morphological freshness comparable to recently formed phreatomagmatic eruption craters elsewhere. The median LVF cinder/spatter cone has a basal diameter of 600 m, a height of 75 m, a volume of 0.009 km 3 and a model total erupted volume of 0.014 km 3 . Variation in cone basal diameter to height ratios indicates that the age of some prehistoric cones may not exceed a few centuries, and morphological classification identifies the youngest prehistoric vents on the northern flanks of the central edifice. Historic activity from vents on the western flanks of Lamongan produced at least ∼0.05 km 3 of basaltic to basaltic andesite lava. Resurfacing rates at Lamongan in the 19th Century imply an age of ∼900–2100 years for the surface of the volcano. The steady-state eruptive rate from 1843–1898 is evaluated as 0.025 m 3 s −1 , which is low in comparison to estimates from many presently active systems. Using eruptive rate and volume data, the age of the LVF is estimated as between 13 and 40 ka, placing it among the youngest dated Indonesian volcanoes. Complex regional tectonics in conjunction with magmatic pressure have probably been the major influences on the distribution of volcanism in the LVF. The occurrence of maar-forming eruptions may have been controlled by a porous substrate, possibly a deposit from the Holocene Iyang–Argapura complex to the east. Volcanic hazards from future eruptions in the LVF include base surges, ash flows, ashfall and ejected blocks associated with phreatomagmatic activity, and ashfall and ejecta from magmatic eruptions.

Stratospheric volcanic ash emissions from the 13 February 2014 Kelut eruption

Mount Kelut (Indonesia) erupted explosively around 15:50 UT on 13 February 2014 sending ash and gases into the stratosphere. Satellite ash retrievals and dispersion transport modeling are combined within an inversion framework to estimate the volcanic ash source term and to study ash transport. The estimated source term suggests that most of the ash was injected to altitudes of 16–17 km, in agreement with space-based lidar data. Modeled ash concentrations along the flight track of a commercial aircraft that encountered the ash cloud indicate that it flew under the main ash cloud and encountered maximum ash concentrations of 9 ± 3 mg m−3, mean concentrations of 2 ± 1 mg m−3over a period of 10–11 min of the flight, giving a dosage of 1.2 ± 0.3 g s m−3. Satellite data could not be used directly to observe the ash cloud encountered by the aircraft, whereas inverse modeling revealed its presence.

Influence of the 2008 Kasatochi volcanic eruption on sulfurous and carbonaceous aerosol constituents in the lower stratosphere

Influences on stratospheric aerosol during the first four months following the eruption of Kasatochi volcano (Alaska) were studied using observations at 10700 +/- 600 m altitude from the CARIBIC platform. Collected aerosol samples were analyzed for elemental constituents. Particle number concentrations were recorded in three size intervals together with ozone mixing ratios and slant column densities of SO2. The eruption increased particulate sulfur concentrations by a factor of up to 10 compared to periods before the eruption (1999-2002 and 2005-August 2008). Three to four months later, the concentration was still elevated by a factor of 3 in the lowermost stratosphere at northern midlatitudes. Besides sulfur, the Kasatochi aerosol contained a significant carbonaceous component and ash that declined in time after the eruption. The carbon-to-sulfur mass concentration ratio of the volcanic aerosol was 2.6 seven days after the eruption and reached 1.2 after 3 - 4 months. Citation: Martinsson, B. G., C. A. M. Brenninkmeijer, S. A. Carn, M. Hermann, K.-P. Heue, P. F. J. van Velthoven, and A. Zahn (2009), Influence of the 2008 Kasatochi volcanic eruption on sulfurous and carbonaceous aerosol constituents in the lower stratosphere, Geophys. Res. Lett., 36, L12813, doi: 10.1029/2009GL038735. (Less)