Landslides（[地质]山崩）causedbythecollapseofunstablevolcanoesareoneofthemajordangersofvolcaniceruptions.Amethodtodetectlong-termmovementsofthesemountainsusingsatelliteimagescouldhelpidentifypreviouslyoverlookedinstabilityatsomevolcanoes,accordingtoPennStatescientists.

"Wheneverthereisalargevolcaniceruption,thereisachancethatifaflank（侧翼）ofthevolcanoisunstabletherecouldbeacollapse,"saidJuditGonzalez-Santana,adoctoralstudentintheDepartmentofGeosciences."Tobetterexplorethishazard（危险）,weappliedanincreasinglypopularandmoresensitivetime-seriesmethodtolookatthesemovements,orsurfacedeformation（变形）,overlongertimeperiods."

Usingthetime-seriestechnique,thescientistsfoundsurfacedeformationrelatedtoflankmotion（移动）hadoccurredatPacaya,anactivevolcanoinGuatemala,fromtowhenthevolcanowaslargelyquiet,andincreasedleadinguptoaneruptionin.Previousworkhadnotidentifiedflankmotionduringthistime,thescientistssaid.

Pacaya：帕卡亚火山是一座位于危地马拉的复合型活火山，坐落在沿太平洋的中美洲火山弧上，坐标14.°N90.°W，海拔米，距世界遗产安地瓜古城和危地马拉首都拉奥罗拉国际机场的直线距离各约20公里。

Guatemala：危地马拉共和国，通称危地马拉，位于中美洲，西濒太平洋，东临加勒比海，北与墨西哥接壤，东北邻伯利兹，东南邻洪都拉斯和萨尔瓦多。

"Peoplehavelookedatthatvolcanowithsatelliteremotesensingbutdidnotdetectthislong-termflankmotionorcreep,（慢慢地移动）"saidChristelleWauthier,associateprofessorofgeosciences."Becausethesurfacedeformationchangesareprettysmallperyear,itcaneasilybebelowthedetectionlimitsofconventionalmethods,butstillwithinthelimitsofJuditsworkusingatime-seriesapproach."

Scientiststracksurfacedeformationusingradarsatellitessensitiveenoughtospotchangesofjustafewinchesontheground.Comparingtwooftheseimagesusingtheconventional（传统的）InterferometricSyntheticApertureRadar(InSAR)techniquecreatesaninterferogram（干涉图）,essentiallyamapofsurfacemovement.ButthequalityoftheInSARresultsdecreaseswiththetimeseparatingtwoimagesandcanbeaffectedbyevensmallchanges,likefromvegetation（植物）growthorabuildupofashspewedfromavolcano,thescientistssaid.