Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography ISSN 1598-4850(Print) Vol. 34, No. 4, 357-372, 2016 ISSN 2288-260X(Online) http://dx.doi.org/10.7848/ksgpc.2016.34.4.357 Original article Sustainable Surface Deformation Related with 2006 Augustine Volcano Eruption in Alaska Measured Using GPS and InSAR Techniques Lee, Seulki1)ㆍKim, Sukyung2)ㆍLee, Changwook3) Abstract Augustine volcano, located along the Aleutian Arc, is one of the most active volcanoes in Alaska and nearby islands, with seven eruptions occurring between 1812 and 2006. This study monitored the surface displacement before and after the most recent 2006 eruption. For analysis, we conducted a time-series analysis on data observed at the permanent GPS(Global Positioning System) observation stations in Augustine Island between 2005 and 2011. According to the surface displacement analysis results based on GPS data, the movement of the surface inflation at the average speed of 2.3 cm/year three months prior to the eruption has been clearly observed, with the post-eruption surface deflation at the speed of 1.6 cm/year. To compare surface displacements measurement by GPS observation, ENVISAT(Environmental satellite) radar satellite data were collected between 2003 and 2010 and processed the SBAS(Small Baseline Subset) method, one of the time-series analysis techniques using multiple InSAR(Interferometric Synthetic Aperture Radar) data sets. This result represents 0.97 correlation value between GPS and InSAR time-series surface displacements. This research has been completed precise surface deformation using GPS and time-series InSAR methods for a detection of precursor symptom on Augustine volcano. Keywords : Surface Deformation, GPS, InSAR, SBAS, Volcano Monitoring 1. Introduction important to minimize the damage of a volcanic eruption by broadcasting warnings as early as possible, it is not easy to Of the life-threatening natural disasters such as do so with current technology (Pieri and Abrams, 2005). The earthquakes, tsunamis, and volcanic activity, those created precursor signs of volcanic activity that have been known to by orogenic movements are harder to predict and cause more us include increases in volcanic earthquake frequency and property damage and human casualties. The natural disasters changes in volcanic gas emissions, crust shape, geothermal originating from volcanic activity can devastate cities, heat level, and hydrological conditions (Xu et al., 2012). Of farmlands, and vegetation with flowing lava and pyroclastic the precursor signs, ground deformation caused by magma flow, with follow-on effects like earthquakes, landslides, chamber movements observed hours or days before the and tsunamis. In addition, the spread of volcanic ash may eruption is one of the most common eruptive activities. It disrupt air travel through a wide area for an extensive period is possible to estimate the time of eruption based on change while causing respiratory problems for residents near the of the shape and form of ground deformation. In general, eruption site (Waythomas and Waitt, 1998). Although it is shallow magma chambers close to the surface, commonly Received 2016. 07. 21, Revised 2016. 08. 18, Accepted 2016. 08. 26 1) Member, Division of Science Education, Kangwon National University (E-mail : [email protected]) 2) Department of Geoinformation Engineering, Sejong University (E-mail : [email protected]) 3) Corresponding Author, Member, Division of Science Education, Kangwon National University (E-mail : [email protected]) This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 357 Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography, Vol. 34, No. 4, 357-372, 2016 around several km under the surface, cause bloating of the information unlike InSAR that provides the LOS(Line-Of- surface due to the mounting pressure within the chamber Sight) directions of the displacement only (Larson et al., (Yazdanparast and Vosooghi, 2013). 2010). As each observational technique has pros and cons, it To monitor and predict volcanic activities, a variety of is advisable to use multiple techniques in a complementary sensors, including seismometer, clinometer, gravimeter, way to ensure a more precise outcome. As the two techniques CGPS(Continuous Global Positioning System), and satellite of InSAR and GPS can offset problems of one approach by image have been used. In particular, high-tech geodetic the other, their simultaneous use improves the precision of survey tools such as the GPS and InSAR have been used surface displacement monitoring (Lee et al., 2010). since the 1980s and have contributed to volcanic monitoring In this study, ENVISAT data and GPS data, collected and research in meaningful ways (Lu, 2005). The recently from June 2003 to August 2010, were simultaneously used developed InSAR technique, which uses two or more to measure the movements before and after the eruption SAR(Synthetic Aperture Radar) images to generate maps of of Augustine volcano in Alaska, which had a record of surface deformation or digital elevation, using differences in discharge in 2006 (Berardino et al., 2002). This research the phase of the waves returning to the satellite, can monitor alert us to important information of symptom for volcanic displacements over several tens of square kilometers with eruption through quantitative analysis from time-series several millimeter- or centimeter-precision, which is ideal surface deformation using GPS and InSAR techniques. for observing earthquake, volcano, glacier, and landslide movements (Jo et al., 2015; Lee et al., 2013; Lee, 2014). The 2. Study Area and Dataset remote-sensing technology like InSAR is widely used in volcano research because of its ability to make high-spatial- 2.1 Study area resolution displacement observations in mountains and other Augustine Island, the main locus of this study, is located difficult to access areas (Jónsson et al., 2002; Pritchard and in the southwestern Cook Inlet, about 290 km southwest Simons, 2004). of Anchorage. The island has a land area of 90 km2, with Although GPS was originally developed for military the highest peak reaching 1,260 m (Fig. 1(a)) (Waythomas purposes, it is now used more widely for civilian applications and Waitt, 1998). The Aleutian Islands, of which Augustine including land surveying, navigation, communication, and volcano is a part, belong to a subduction zone at which the weather monitoring. With GPS devices, displacements of Pacific and North American plates meet, with as many as 57 the earth’s crust and faults can be measured with millimeter- volcanoes nearby (Michel et al., 2009). Of these, Augustine precision, which is useful for geophysics research. However, volcano is one of the most active (Beget and Kowalik, 2006; GPS devices that must be installed on the earth’s surface Miller et al., 1998). Since the first recorded eruption in 1812, for observing surface displacements only from the station the volcano has flared up in 1883, 1935, 1964-65, 1976, and where the antenna is set up. Alternatively, InSAR data could 1986. After a 20-year hiatus, it again exploded in January provide the short spatial scale surface deformation such 2006 (Power et al., 2006). as every coherence points within SAR images practically Of the seven eruptions, the most violent 1883 episode lacking in GPS data (Wei et al., 2010). In particular, the use caused a tsunami of 7.5-9.0 m as debris avalanche on the of GPS devices in volcanoes is limited since the antenna northern slope of the island poured onto the sea and caused is easily damaged by eruptions and weather conditions repercussions as far as the Kenai Peninsula in English Bay 80 may affect data collection (Cervelli et al., 2006; Lisowski km away (Miller et al., 1998; Waythomas and Waitt, 1998). et al., 2008). When comparing it to the InSAR technique’s As for the 1976 eruption, which was closest in pattern to the relatively longer data collection cycle, the GPS method is 2006 event, there had been precursor signs nine months before superior in that it can measure surface displacements at the the eruption with a notable increase in earthquake activity, time of eruption and collect three-dimensional locational including 13 volcanic eruptions for three days since January 358 Sustainable Surface Deformation Related with 2006 Augustine Volcano Eruption in Alaska Measured Using GPS and InSAR Techniques 22. Following a 12-day lull, volcanic activity increased slightly between February 6 and 15, which created lithic-rich pyroclastic flows and lava domes in the northern slope. From April 13 to 18, there were final eruptions that accompanied lava dome expansion and block-and-ash flows (Coombset al., 2010; Larsen et al., 2010). The 1986 episode showed similar patterns to the 2006 event and the one in 1976, in that large pyroclastic flows gushed out in the beginning of the eruption and moved through the northern slope reaching a point 5 km from the northern coast (Miller et al., 1998). The precursor signs for the eruption in 2006 first appeared in May 2005, with a steady increase in small tremors in and around the crater (Cervelli et al., 2006). Fig. 1(b) represents earthquake epicenters with blue circles and west-east (A-A’) and north-south (B-B’) cross section showing earthquake hypocenters associated with 2006 eruption at Augustine volcano, respectively. Red and blue cross represents depth of hypocenters before and after the 2006 eruption. Aster satellite image displays surface temperature after the 2006 eruption on pyroclastic flow deposit area at northern part of Augustine volcano. Aster satellite data need to be converted to radiance from DNs(Digital Numbers) for thermal bands. Also, Brightness temperature was converted using spectral radiance (Ghulam, 2009). Moreover, Aster satellite image can display surface Fig.