Eos, Vol. 87, No. 23, 6 June 2006 Imaging a Growing Lava Dome With a Portable Radar PAGES 2 2 6 , 2 2 8 The tiny Caribbean island of Montserrat has b e e n in a state of crisis since the Soufriere Hills Volcano (SHV) began its current erup­ tion in July 1995. With its main town, Plym­ outh, destroyed by pyroclastic flows in 1997, the islanders who have remained have had to rebuild their society on the northern half of the island under varying degrees of threat from the volcano to the south. During this time, the Montserrat government continues to receive advice on the volcanic hazards from the Montserrat Volcano Observatory (MVO). The continuing eruption has provided a wealth of research opportunities for many international groups who sought to study the growth and repeated partial destruction of a Peleean andesitic lava dome. There have been three episodes of d o m e growth: November 1995 through March 1998, November 1999 through July 2003, and August 2005 to present. Pyroclastic flows and explosions have been the main source of hazard.The pyroclastic flows have been generated mainly by gravitational collapse of the lava dome, but also by collapse of explosive ash columns. The dome collapses tend to o c c u r from the area of the dome where new lava is being added. Similarly collapses are more likely when the rate of lava extrusion varies. Also, the propensity of explosive evacu­ ation of the magma in the conduit is partly controlled by the magma supply rate, with high rates favoring explosions. Hence, scientists at MVO seek to monitor both the shape of the growing d o m e and its rate of growth, to help evaluate future hazard­ ous behavior. One of the big problems they face in this task is cloud cover. Moisture­laden air is blown westward by the trade winds up the volcano's slopes, where it forms clouds. Days or even weeks c a n go by without this orographic cloud c a p lifting to reveal the activ­ ity at the lava dome, whose summit has varied between 700 and 1100 meters above sea level. A potential solution to this problem is a pro­ totype instrument designed and built by the authors of this article: an all­weather volcano topography imaging sensor (AVTIS) [Wadge et al, 2005] that allows volcanologists to 'see' the growing d o m e through cloud and to quantify its shape and rate of growth. The AVTIS antenna and measures the distance to the volcano's surface with a resolution of about one meter over a range of up to about seven kilometers. A raster image is constructed at a rate of four samples per second using a motor­ ized pan and tilt gimbal with selectable angular increments. In addition, in radiometric mode, the naturally emitted radiation is measured as an apparent brightness temperature with a thermal resolution of about 5 K. Thus the radarometer captures synchro­ nized image pairs of range (topography) and surface temperature data (technical details are given by Macfarlane and Robertson [2004, 2005] and at http://www.st­andrews.ac.uk/ ­mmwave/mmwave/avtis.shtml). The active radar functionality of AVTIS was tested, and subsequently modified, at Montserrat in J u n e 2004 [Wadge etal, 2005] and at Arenal Volca­ no, Costa Rica, in April­May 2005 [Macfarlane et al, 2 0 0 6 ] , but not the radiometer mode. AVTIS is o n e of several ground­based radar instruments that are being applied to the study of the dynamics of volcanic activity. These include two instruments that use Dop­ pler radar information to measure the relative et motion of volcanic fragments [Donnadieu al, 2005; Voege etal, 2005].AVTIS,however, is distinct from these other systems in being a three­dimensional (3­D) imaging (as opposed to a 1­D measurement) instrument, operating at a higher frequency, that gathers surface data rather than fragment motion information. It is the first such ground­based instrument. Deployment at Montserrat in October-November 2005 Prior to the latest resumption of d o m e growth, there were two months of precursory phreato­magmatic explosions, caused by the interaction of magma with ground water, and fracturing of the crater area. However the start of lava extrusion sometime during the first week of August 2005 was not observed b e c a u s e of dense cloud cover. The new lava d o m e grew on the floor of English's Crater (a horseshoe­shaped crater open to the ENE) within which the lava d o m e first began to grow in 1995.The morphology of this crater was last modified in a major way by the collapse of the previous lava d o m e on 12­13 July 2003.This involved about 200 million c u b i c meters of material and removed about 4 0 0 meters of d o m e rock from above the vent, sending most into the s e a to and the east as pyroclastic flows [Edmonds Herd, 2005].The 2003 d o m e largely disap­ peared except for remnants adjacent to the crater walls and a transverse NW­SE ridge just downslope from the vent. The 150­ to 200­meter­high walls of English's Crater and the transverse ridge hid the newly growing d o m e from view, except from the air and viewpoints on the crater rim.The best of these viewpoints, on Perche's Mountain, was about 1200 meters to the ESE of the d o m e Fig, 1. AVTIS in operation at Soufriere Hills Volcano on 4 November 2005. The tripod-mounted instrument is scanning the growing lava dome, framed by steam on the left of the image. Original color image appears at the back of this volume. Radarometer AVTIS is a dual­mode active radar and passive radiometer (hence radarometer) that operates in the millimeter­wave part of the spectrum.The frequency­modulated continuous wave radar (94 gigahertz) uses a 30­centimeter­diameter B Y G . WADGE, D . G . MACFARLANE, M . R . JAMES, H . M . ODBERT, L . J . APPLEGARTH, H . PINKERTON, D . A . R O B ­ ERTSON, S . C . LOUGHLIN, M . STRUTT, G . RYAN, AND P N . DUNKLEY Fig. 2. Qualitative comparison of (left) the thermal IR (FLIR Systems) image and (right) the millimeter-wave (AVTIS) image of the surface brightness temperature of the southeast side of the Soufriere Hills Volcano lava dome on 4 November 2005. Areas A, B, and C were the main loci for dome growth during the previous nine days. Original color image appears at the back of this volume. Eos, Vol. 87, No. 23, 6 June 2006 5 Over these areas ( ~ 1 0 square meters), the vertical height differences for the two surfaces interpolated over a two­meter­resolution grid had an RMS residual error of 2.3 meters. B e c a u s e of increasing obscuration of the rear wall of the crater by the growing dome, the areas covered by observed points in the two data sets are not identical.To exclude errors due to comparison of areas interpolated over regions of data gap, only those areas of the d o m e that were directly observable on both days have b e e n included when making vol­ u m e c h a n g e calculations. However, visual and thermal observations indicated that the loci of growth during this period occurred on the Perche's side of the dome. The difference in the lava dome surfaces measured between 25 October and 4 Novem­ ber is shown in Figure 3. Most of the new material was added in three lobes on the south and southeast sides of the dome. These lobes correspond to areas that are hottest in the temperature image (Figure 2).The vol­ ume added to the d o m e was 9.9 x 10 c u b i c meters in 10 days, an average rate of 1.1 ± 0.1 c u b i c meters per s e c o n d . During the first few weeks of dome growth in 2005, MVO made estimates of the size of the d o m e and the rate of growth based on photography and laser ranging.These showed that the d o m e had formed an elongate shape as it piled up against the transverse ridge and that the growth rates were in the range 0.5­1.0 cubic meters per second. However, early in October 2005 the rate of growth seemed to increase and MVO b e c a m e concerned that the magma flux rate might accelerate to higher, more dangerous, levels (e.g., more than five c u b i c meters per s e c o n d ) , as had happened earlier in the eruption [Sparks et al, 1998].The AVTIS­measured growth rate of the lava dome was a much more accurate measurement than could have b e e n attained by any other means during a period of cloudiness.The rate of less than two c u b i c meters per second reassured MVO that the new phase of the eruption was not accelerating to a more hazardous state. 5 Fig. 3. (a) Shaded relief orthographic projection of the lava dome and crater surface imaged by AVTIS from Perches Mountain on 25 October 2005 (offset coordinates relative to radar position). (b) Ten days of growth of the lava dome (colored by vertical height difference) between as measured by AVTIS superimposed on the shaded relief image. 25 October and 4 November (c) Surface brightness temperature data measured by AVTIS on 4 November. Original color image appears at the back of this volume. and about 100 meters higher (Figure 1). Since the Perche's Mountain site is only accessible by helicopter, this restricted how often the AVTIS could b e deployed there. This article reports on the result of two days of measurements of the growing lava d o m e from Perche's Mountain, from 25 O c t o b e r and 4 November 2005. On both days, the Perche's Mountain site was o c c u p i e d for just over three hours, with visibility varying from com­ pletely clear to total cloud cover. Topographic data covering the growing dome, the trans­ verse ridge, and the surrounding crater were collected using AVTIS in its active radar m o d e regardless of viewing conditions. Images were constructed over a 13° x 20° field of view at 0.125° increments. Ash clouds produced by rockfall and gas venting from the d o m e were completely transparent to the radar. Additionally, on 4 November, a surface tem­ perature image of the dome was collected using the passive radiometer mode, and a FLIR Systems infrared (IR) camera simultaneously captured thermal imagery for comparison. This was the first successful test of the AVTIS radiometric mode at a volcanic target, and probably is the first ever passive millimeter­ wave image of an active volcano. Although the image resolution of millimeter­wave radiom­ etry is fundamentally coarser than IR, qualita­ tive agreement is good, with easily identifiable thermal features on the d o m e corresponding to those seen in IR imagery (Figure 2 ) . The instrument was installed on the same tripod (undisturbed between occupations), which provided an initial coarse registration of the data sets. The relative registration was then refined by rotating the 4 November image coordinate system in order to minimize the differences between surfaces interpolated over areas of the crater that had not b e e n influenced by the growing dome. Ideally a set of AVTIS­type instruments would sit at appropriate viewpoints and continuously monitor the growth of the lava dome to pro­ vide MVO with an operational stream of data, independent of weather.There are a number of improvements that need to be made before such an ideal can b e realized.These include making the instrument more autonomous so that it can collect, store, and telemeter data from remote sites and b e usable by observa­ tory staff.With these improvements, this type of instrument can open up an exciting new capa­ bility in volcanology enabling volcanologists to obtain detailed time series data on the growth of domes and lava flows.This will provide vital information on the hazardous state of the eruption and on the dynamics of the volcanic system as a whole. Acknowledgments We are grateful for the financial support of the U.K. Natural Environment Research Council Eos, Vol. 87, No. 23, 6 June 2006 and the skill of the pilots working for Carib­ b e a n Helicopters. References Donnadieu, F, G. Dubosclard, R. Cordress.T. Druitt, C. Hervier, J. Kornprobst, J.-F Lenat, P Allard, and M.Coltelli ( 2 0 0 5 ) , Remotely monitoring volcanic activity with ground-based Doppler radar, Eos Trans. AGU,86(2X),20\,204. Edmonds, M., and R.A. Herd ( 2 0 0 5 ) , Inland-directed base surge generated by the explosive interaction of pyroclastic flows and seawater at Soufriere Hills volcano, Montserrat, Geology, 33, 2 4 5 - 2 4 8 . Macfarlane,D.G.,and D.A.Robertson ( 2 0 0 4 ) , A 9 4 GHz dual-mode active/passive image for remote sensing,Proc.SPIEInt.Soc. Opt.Eng., 5619, 7 0 - 8 1 . Macfarlane,D.G.,and D.A.Robertson ( 2 0 0 5 ) , L o n g range, high resolution 94 GHz FMCW imaging radar (AVTIS), paper presented at the 30th Inter- national Conference on Infrared a n d Millimeter Waves, US. Nav. Res. Lab., Williamsburg, Va., 1 9 - 2 3 Sept. Macfarlane, D. G., G. Wadge, D. A. Robertson, M. R. Responses interpreted as having general sup­ port included (in order): improving methods for determining measurement uncertainty; Geoffrey Wadge, Environmental Systems S c i e n c e Centre, University of Reading, U.K.; David G. Macfarlane, School of Physics and Astronomy University of topographic mapping millimeter wave radar at St. Andrews, St. Andrews, U.K.; Michael R. J a m e s , Envi- an active lava flow, Geophys. Res. Lett., 33, L03301, doi:10.1029/2005GL025005. Sparks, R.S. J., et al. ( 1 9 9 8 ) , Magma production and growth of the lava d o m e of the Soufriere Hills Volcano, Montserrat, West Indies: November 1995 to December 1997, Geophys. Res. Lett., 2 5 ( 1 8 ) , 3421-3424. Voege,M.,M.Hort,and R.Seyfried ( 2 0 0 5 ) , Monitoring v o l c a n o eruptions and lava d o m e s with Doppler radar,£bs Trans. AGU, 5 6 ( 5 1 ) , 5 3 7 , 5 4 1 . Wadge, G.,et al. ( 2 0 0 5 ) , AVTIS: A millimetre-wave ronment Centre, Lancaster University, U.K.; Henry M. Odbert, Environmental Systems S c i e n c e Centre, University of Reading, U.K.; L. J a n e Applegarth and H. Pinkerton, Environment Centre, Lancaster University U.K.; Duncan A. Robertson, School of Physics and Astronomy, University of St. Andrews, St. Andrews, U.K.; Susan C. Loughlin, Michael Strutt, Graham Ryan, and Peter N. Dunkley Montserrat Volcano Observatory/British Geological Survey, Keyworth, U.K.; E-mail: gw@mail.nerc-essc.ac.uk ground based instrument for v o l c a n o remote sens- ing, J.Volcanol. Geotherm.Res., 146, 3 0 7 - 3 1 8 . Survey Provides Guidance for Consortium's Hydrologic Measurement Facility The Consortium of Universities for the Advancement of Hydrologic Sciences, Inc. (CUAHSI) began the Hydrologic Measure­ ment Facility (HMF) program in J u n e 2005 to advance hydrologic measurement capability within the research community. To provide guidance for this effort, a recent survey assessed the level of need among the hydrological sci­ e n c e s community for community instruments and facilities.The survey aimed to identify tech­ nologies and methodologies that could make major advances in the hydrologic sciences. Between 1 November 2005 and 15 January 2 0 0 6 , 3 6 3 responses were returned. (45% from hydrologists, 15% soil scientists, 12% geophysi­ cists, 11% biogeochemists, 3% ecologists, 3% geomorphologists, and 11% other disciplines). One question asked respondents to identify what was most needed to make progress in hydrologic sciences, among 23 options about measurements, instruments, and facilities. Results showed that 80.6 percent of respon­ dents favored improving the integration between measurement and modeling meth­ ods; 79.7 percent supported improving spatial resolution of measurements; 77.3 percent thought the ability to make more/better mea­ surements, for example, through distributed sensor networks was important; and 76.4 percent thought that improving the ability to measure and quantify water in the subsurface was necessary There was also strong support for providing a c c e s s to equipment costing over $20,000, and for accompanying that a c c e s s with technical support for deployment and data interpretation. information J a m e s , and H.Pinkerton ( 2 0 0 6 ) , Use of a portable NEWS PAGE 2 2 2 Author improving the temporal resolution of measure­ ments; developing cross­scale, multiprocess observational platforms; improving hydrologi­ cal models; improving methods of sensor cali­ bration; and developing new tracer methods. Respondents identified and prioritized what the HMF's goals should be.The strongest response (62.7%) was received for conduct­ ing research and development into new hydrological measurement devices. Other areas drawing strong support were (in order): development of new methods and instru­ ments; comparisons of sensors; preparing a comprehensive handbook of measurement techniques; and integrating measurement and modeling approaches. Of the respondents, 59.0 percent supported having a single HMF research and develop­ ment center; less than 4.0 percent wanted a stand­alone rental facility. It is noteworthy that CUAHSI has now signed a Cooperative Research and Development Agreement with the U.S. Geological Survey's Hydrological Instrument Facility to provide a c c e s s to stan­ dard hydrological measurement equipment— resolving a need that was ranked as a lower priority—at no direct cost to CUAHSI or the US. National S c i e n c e Foundation (NSF). The survey addressed the issue of developing a shared pool of equipment. NSF has long held that this would b e a desirable HMF function, allowing NSF to pay for equipment that would be broadly accessible to qualified researchers. The consensus view of respondents was that instrumentation should b e owned and main­ tained by CUAHSI under the HMF umbrella, and that provision should b e made to allow the entire community of investigators to lease or share this supported equipment. Respondents indicated that the types of equipment they would most like to have a c c e s s to included: atmospheric profilers (e.g., radio acoustic sounding system, lidar,and sonic detection and ranging), ground­based and airborne geophysical equipment, water quality sensors, soil moisture measurement systems, weather radar, and atmospheric flux towers. This survey was useful in providing guid­ a n c e for the CUAHSI HMf; whose mission needs to address the following: 1. Identification and purchase of high­cost equipment for community use under the CUAHSI HMF umbrella, with support dedi­ cated to developing methods and producing the correct interpretation of the data. 2. Provision of a facility/laboratory for instru­ ment research and development specifically targeted at hydrology. 3. Support of distributed hydrologic mea­ surements under the CUAHSI HMF umbrella. 4. Facilitation of the development and dis­ semination of methodologies for hydrologic measurements in watersheds, including ways to better integrate measurements and models, and to better assess measurement uncertainty. A full report of the survey results, includ­ ing all written c o m m e n t s submitted, will b e published as a CUAHSI technical report on the CUAHSI Website: http://www.cuahsi.org This material is based upon work supported by NSF under grants EAR­0326064 and EAR­ 0447287. Any opinions, findings, and conclu­ sions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF — D A V I D ROBINSON, Department of Geophysics, Stanford University, Calif., darob@stanford.edu; JOHN SELKER, Department of Biological and Ecological Engineering, Oregon State University, Corvalis; BRECK BOWDEN, Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington; JONATHAN DUNCAN, CUAHSl.Washington, D C ; JOHN DURANT, Department of Civil and Environmental Engineering,Tufts University, Medford, Mass.; RlCK HOOPER, CUAHSI,Washington, D C ; JENNIFER JACOBS, Department of Civil Engineering, University of New Hampshire, Durham; and ROSE­ MARY KNIGHT, Department of Geophysics, Stanford University, Calif. Eos,Vol. 87, No. 2 3 , 6 June 2006 I o < s • uc H ~ 1 • UC­2 • UC­3 B u c _ 4 • | UE­1 UE­2 Macro Fauna Pofychaetes • Crustaceans H Mdfuscs { | Page 225 Sipuncuia EcNnodermata Nemertea Nematoda Other Taxa pH — 8 — Temperature — • — Foraminifers Sand ­ • Foraminifers Rubble As in pore water • • } Bbavailabie As Arsenic PI 1 Distance from Vent 4 (m) Fig. 3. Physical, chemical, and biological trends stepping away from the area of active venting in Tutum Bay. From left to right, the y-axes are number of foraminifera shells per gram of sediment, concentrations of As in milligrams per kilogram (sediment) and milligrams per liter (pore water), in °C. The values for As in pore waters were multiplied by a factor of 10*; pH, and temperature the value at a distance of one meter is 0.9 milligrams per liter. The macro fauna pie at a distance of 300 meters represents a sample taken at the reference site. In the legend on the right side, UC and UE indicate 'uncultured Crenarchaeota and 'uncultured Euryarchaeota,'respectively. Fig. 1. AVTIS in operation at Soufriere Hills Volcano on 4 November 2005. The tripod-mounted instrument is scanning the growing lava dome, framed by steam on the left of the image. Page 226 Fig. 2. Qualitative comparison of (left) the thermal IR (FLIR Systems) image and (right) the millimeter-wave (AVTIS) image of the surface brightness temperature of the southeast side of the Soufriere Hills Volcano lava dome on 4 November 2005. Areas A, B, and C were the main loci for dome growth during the previous nine days. Eos, Vol. 87, No. 2 3 , 6 June 2006 Page 226 Fig. 3. (a) Shaded relief orthographic projection of the lava dome and crater surface imaged by AVTIS from Perches Mountain on 25 October 2005 (offset coordinates relative to radar position). between (b) Ten days of growth of the lava dome (colored by vertical height difference) as measured by AVTIS superimposed on the shaded relief image. 25 October and 4 November (c) Surface brightness temperature data measured by AVTIS on 4 November.