PRINS OF GLACIOLOGY
PRINS OF GLACIOLOGY ESS 431
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This 24 page Class Notes was uploaded by Miss Jeanette Keebler on Wednesday September 9, 2015. The Class Notes belongs to ESS 431 at University of Washington taught by Staff in Fall. Since its upload, it has received 16 views. For similar materials see /class/192661/ess-431-university-of-washington in Earth And Space Sciences at University of Washington.
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Date Created: 09/09/15
PRINCIPLES OF GLACIOLOGY ESS 431 GLACIER SLIDING and HYDROLOGY OCTOBER 20 2008 Ed Waddington 715 ATG 5434585 edwesswashingt0nedu Midterm a comin One week from today Monday Oct 27 Study questions will be online tomorrow Midterm will consist of a selection from the posted questions Read the hints on writing a test on the class web page Extra discussion session on FridayMonday Sources Andersen BG and HW Borns 1994 The IceAge World Scandinavian University Press Benn DI and DJ A Evans 1998 Glaciers and Glaciation Arnold Drewry D 1984 Glacial Geologic Processes Arnold Hambrey M and J A1ean 2004 Glaciers 1St and 2Ild editions Cambridge Hooke R LeB 2005 Principles of Glacier Mechanics 2Ild edition Cambridge Paterson WSB 1994 The Physics of Glaciers 3rd edition Pergamon Wingham DJ et al 2006 Rapid discharge connects Antarctic subglacial lakes Nature 4404660 10331036 James Hill New York Times Lecture notes from CF Raymond Importance of Sliding Internal deformation ud is always present Sliding contribution to ice transport us O X ud eg frozen bed us 10Ngtlt ud eg glacier surges and ice streams N can be as high as 3 In typical temperate mountain glaciers it is commonly supposed that Ice transport due to sliding Ice transport due to internal deformation What s it like under a glacier Smooth clean bedrock x V 00 l Frozen ground tundra gravel till Icequot Soft marlne mud mud g fr Cant sediments39 I Glacial till unsorted gravel mud Soft wet deformable Hard overconsolidated Wet thawing geothermal ux frictional heat Wet freezing ice fingers into pores Water is very important 0 Meltwater from surface 0 Meltwater from the bed 0 Drainage through till Water pressure What does water do in a glacier Hardbed sliding W P WWW 1C6 Water layer Force equilibrium provides local requires difference in Illbricaticn pressure across the bump What allows slip to occur Ice Avalanche lt gt 39 r w r r Apnrnximavely ll Miles at Dasvrucnan September 20 2002 North Ossetia Russian Caucasus opart of Maili Glacier broke off and avalanched 20gtlt106 tonnes of ice rock and mud swept 16 km through Karmadon Gorge at lOO km per hour l40 fatalities Village of Nizhny Karmadon destroyed James Hill New York Times Tombstone Model J Weertman 1957 A simple starting model for sliding If ice is not accelerating off the mountain ie an ice avalanche then there must be a restraining force to balance the downslope shear stress 239 0 g h sin9 h 2 ice thickness 9 surface slope On Area Xx Force F 7X2 stress xArea Tombstone face F0rce 712 is supported entirely by uphill face of bump This face has area L2 Pressure stress on that face is P 712 L2 forceArea High pressure depresses freezing point ATcP c7gtlt103980CPa391 gt AT cTIZL2 Can ice slide past a Bump How fast ice can move past bump depends on how fast heat can get back through bump Heat ux Q depends on temperature gradient ATL Fourier s Law Q K ATL K rock conductivity 22 W m391 deg 391 L rock scale length m AT c T l2 L2 Sliding Speed by R tl 39t f w zli l fl 9 k Regelatlon In t1me At heat ux Q W m392 Ax delivered to Area 1 m2 of rock face can melt a volume of ice V energy delivered energy to melt 11113 V Q XArea XAt pH H heat of fusion 331 J kg391 p ice density 900 kg m393 Volume Vis face area L2 times amount Ax melted off at face V L2XAX Ax KCT 22 Put it all together Uslz39de E pHL P Example of sliding speed 2 IfL 002 m slide E l z 7 02 rn pHL L 395 105 Pa 2W m 1 deg 1 7gtlt10 8 deg Pet 11051361 022m2 We 900kgm 333x105Jkg lonzm 0022m2 z2gtlt107ms1 z 2X107ms1gtlt3gtlt107syr1z 6myr 1 How will sliding speed change if bumps are bigger Can ice ow around bumps x is compressive stress in ice upstream of bump Ice knows that bump is there for a distance L0 upstream one large bump stresses a bigger volume of ice compared to many smaller faces With the same total restraining face area as required for force balance Ice deforms in response to stress 3 Glen Flow Law 5x Z A 0x Strain near bumps w 39ALL At Rate of shortening of a line lt upstream from bump x lt m AL Uslide Lgx At L We used Glen ow law gAa x oIce can move faster around larger bumps Regelation Deformation Tradeoff 5 f7 Mt L Regelation allows ice to I slide past small bumps easily Enhanced strain gets ice past large bumps easily At some intermediate scale LLc both processes are equally effective or ineffective ControllingObstacle Size Ac ul 39 r S dlmj I EuknuJ gPaQGQ s i r 399 quot I f I z Reaek 63 i as L amp sac Lt Actual sliding speed is sum of 2 processes At LLc USlide is minimum Bedrocllt bumps with size Lc control sliding speed What assumptions are built into this concept creep velocity U5 1 Flow on 397quot 4o lequally so g Gla01er E300 8 d gt 200 Can Tombstone k MOdel explain 100 basa sliding velocity us these data T D Nisqually River DISCHARGE m3s391 N l 0 Based on HOdge SM39 1974 mammmu mmmumammm J J Glaciol 1369 349369 Water and sliding Water must have some impact on sliding rate HOW Bed Separation and Sliding S SEE mailed to i WM area 0 s 5 1 PW lt Psep as 0 conditions for segudion ml L 39CaVitieS OTMG an m beg cannot form when M uni es n G nP b PwgtPsep 33 St S gt 0 9 CaVities can diam open Speed 20 25 mmh Sliding and Water Pressure Glacier moves faster when water level rises 39 in a hole to bedrock o EJ 53 Why A xl 39q 1 Water depth in borehole I r1 100 60 20 m 15 30 HIV 1 39 30 May 4Juno 1932 4 20 June 1902 Almut Iken 1980 Sliding and Water Pressure 25 mmh S Glac1er moves faster peed when water level r1ses 39 in a hole to bedrock 20 0 13 Borehole is acting as x t a manometer water q level tells us about 39 39 1 Water depth 5 water pressure at the in borehole t r1 m w 20 base of the glac1er m 15 30 May I 4 20Jun 1902 a A 3930MIy 4Juno1932 O x Almut Iken 1980 Sliding and Water Pressure Storglaeiaren HO llIllllllllIT IIIIIIIITTTIII 50 water pressure r l Water pressure 90 Speed 80 70 Speed mm d391 Water Pressure m 60 50 40 lllllIIIJJELIIIIIIIIIIIIIIIIIIIIT Date 30 1111l111111111111111111111411 O 0 15 20 25 30 35 40 July 1993 Only major pressure oscillations are clearly related to Sliding Changes Hanson et al 1998 J Glaciol 44147 359
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