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Information to Users Deformation Of Alaskan Volcanoes Measured Using Sar Interferometry And Gps Item Type Thesis Authors Mann, Doerte Download date 30/09/2021 04:08:10 Link to Item http://hdl.handle.net/11122/8622 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted.Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. ProQuest Information and Learning 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 800-521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NOTE TO USER This reproduction is the best copy availabie. UMI' Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEFORMATION OF ALASKAN VOLCANOES MEASURED USING SAR INTERFEROMETRY AND GPS A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Dorte Mann. Dipl. Geophys. Fairbanks, Alaska August 2002 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3059724 ___ ® UMI UMI Microform 3059724 Copyright 2002 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEFORMATION OF ALASKAN VOLCANOES MEASURED USING SAR INTERFEROMETRY AND GPS By Dorte M ann RECOMMENDED: APPROVED: 0 (a )ogAcJI _____________ Dean. College of Science. Engineering ancl Mathematics Dean m the Graduate School 7 - 9 Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract Geodetic measurements using the Global Positioning System (GPS) and synthetic aperture radar interferometry (InSAR) show deformation of Okmok. Westdahl. and Fisher volcanoes in the Alaska-Aleutian arc. This thesis shows the variety of deformation signals observed, presents models for the observations, and interprets them in terms of underlying processes. InSAR data show deflation of Okmok caldera during its last eruption in 1997, preceded and followed by inflation of smaller magnitude. Modeling shows that the main deformation source, interpreted as a central magma reservoir, is located at 2.5 to 5.0 km depth beneath the approximate center of the caldera, and 5 km away from the active vent. Mass balance calculations and comparison with the long-term eruptive frequency indicate that Okmok may be supplied with magma continuously from a deep source. GPS measurements between 1998 and 2001 show inflation of Westdahl volcano, with a source located about 7 km beneath the summit. The combined subsurface volume increase measured during the GPS and an earlier InSAR observation period [Lu et al., 2000a] ac­ counts for at least 15% more than the volume erupted from Westdahl in 1991-92, suggesting that an eruption of that size could occur at any time. Neighboring Fisher caldera shows subsidence and contraction across the caldera center that is not related to any eruptive activity. The main mechanisms to explain this deforma­ tion are degassing and contractional cooling of a shallow magma body, or depressurization of Fisher’s hydrothermal system, possibly triggered by an earthquake in the vicinity of the caldera in 1999. A systematic coherence analysis of SAR interferograms documents the cooling history of the 1997 Okmok lava flow. The flow is incoherent directly after emplacement, but coherence increases as more time has passed since the eruption, and also the shorter the period spanned by the interferogram. Coherence is regained three years after the eruption. This corresponds to the time when the 20 m thick flow has solidified, indicating that flow mobility is the dominant factor degrading coherence on young lava flows. Based on these results, InSAR coherence analysis can be used to derive the minimum thickness of a lava flow. 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Contents List of Figures ......................................................................................................................... 8 List of Tables ............................................................................................................................. 11 Acknowledgements ................................................................................................................... 12 1 Introduction 13 1.1 General ............................................................................................................................ 13 1.2 Thesis Content and Organization ............................................................................... 15 2 Deformation associated with the 1997 eruption of Okmok volcano, Alaska1 17 2.1 A b s tra c t............................................................................................................................ 17 2.2 Introduction ..................................................................................................................... 18 2.3 O b s e rv a tio n s .................................................................................................................. 19 2.3.1 SAR images and interferograms ..................................................................... 19 2.3.2 Deformation episodes ..................................................................................... 21 2.4 Modeling ........................................................................................................................ 24 2.4.1 The Models .......................................................................................................... 24 2.4.2 Data selection and procedures ........................................................................ 28 2.4.3 Misfit calculation for wrapped interferograms .......................................... 28 2.5 Subsurface volume change, magma volume and pressure change ....................... 29 2.6 Modeling results and interpretation ............................................................................ 31 2.6.1 Pre-eruptive inflation and lateral magma transport (1992-1995) . 31 2.6.2 Co-eruptive deflation (1995-1997) ................................................................. 33 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 2.6.3 Post-eruptive inflation (1997-1998).............................................................. 35 2.6.4 Summary ............................................................................................................ 36 2.7 Discussion ........................................................................................................................ 37 2.7.1 Temporal development of deformation and magma volume .................. 37 2.7.2 Lateral magma transport .............................................................................. 40 2.7.3 Proposed structural model .............................................................................. 41 2.8 Conclusions ..................................................................................................................... 42 2.9 Acknowledgments ........................................................................................................... 43 3 Cooling and structure of the 1997 Okmok lava flow, observed by coherence analysis of SAR interferograms2 44 3.1 A b s tra c t........................................................................................................................... 44 3.2 Introduction ..................................................................................................................... 45 3.3 Coherence analysis ....................................................................................................... 47 3.3.1 Coherence in SAR interferograms ................................................................. 47 3.3.2 Data selection and analysis .......................................................................... 48 3.3.3 Observations ..................................................................................................... 49 3.4 Cooling model ...................................................................................................................
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