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Home My WebLink AboutSUS10023Part I:Text KENNESONG.DEAN NORTHERN REMOTE SENSING LABORATORY GEOPHYSICAL INSTITUTE UNIVERSITY OF ALASKA FAIRBANKS,ALASKA ",.p,mdJOT LAND AND RESOURCE PLANNING SECTION DI VISION OF RESEARCH AND DEVELOPMENT ALASKA DEPARTMENT OF NATURAL RESOURCES MARCH,1980 SURFICIAL GEOLOGY OF THE SUSlTNA-CHULlnIA RIVER AR~.ALASKA Part 1:Text Susitna Basin Planning Background Report Kenneson G.Dean No:othern ~mote Sensing laboratory Geophysical Institute University of Alaska Fairbanks.Alaska prepiared for land and Resource Planning Section Division of Research and Development Alaska Department of Natural Resources UNIV!?P~ITV f,r-f.'1\"KA "Acne E"·r·.......~,.r·'~l "'e-ORMATION J....)C 'j..C ."rER 70:A 'd AN AAC,r.~...99.501 funded in part by NASA Grant NGL 02-001-092 March,1980 6S "225" ,A,J l>.j S t ABSTRACT The landscape of the Susitna-Chulitna River Area of southcentral Alaska is interpreted in fourteen 1 :125,0I..'~scale maps of landform and geologic hazard.The landscape 1s dominated by glacial landforms from late Wisconsin Naptowne G"laciation.Locally,it is continuously being altered by hlOdern active surface processes. The area's landforms consist of drumlinized landfonns including positive relief features composed of till and glaciofluvial deposits,and intervening poorly-drained lowlands often containing lakes.ponds.marshes,swamps and bogs.The extent of the glaciofluvial deposits suggest that water was pre- valent beneath the glacier or flowed in troughs between till ridges beyond the glad ~ice during its recession.Ice-disintegration features along the margins of the fanner glacier resulted from intennixing of till and ~ltwater stream deposits typically distorted by slumping.landfonns on the valley floor grade from disintegration features to drumlinized ridges,drumlins. fluted ground moraine and scoured bedrock to the north. Modern active surface processes often alter the landscape catastrophi- cally,and are called geologic hazards.Geologic ~azards in the study area include flooding,surging glaciers,avalanches and landslides.Surfaces most affected by these hazards are floodpldins,lowlands,and lower mountain slopes. PREFACE The Susitna-Chulitna area investigation was conducted for the land and Resource Plannittg Section of the Alaska Department of Natural Resources (DNR).The study was jointly funded by NASA under grant NGL 02-001-092 and DNR,and was conducted by the Northern Remote Sensing laboratory of the Geophysical Institute.University of Alaska.The investigation is intended to aid ONR in regional planning of relatively inaccessible areas based on inter- pretations of remote sensing data. Map units were verified in the field in accessible portions of the study area.Verified map units were extrapolated to inaccessible areas based on similarity of landfonns. Seven landform maps were prepared at a scale of 1:125,000 and seven geologic hazard maps were prepared at the same scale.These are included in Part 2 of Chi s report. ACKNOWLEDGEMENTS The author would like to thank Thomas H.George for his comments ~nd especially during the field verification.many of the photographs in this report were taken by him;Dr.Richard D.Reger,John H.Miller and Albert E.Belan for reviewing this manuscript.Deborah C.Coccia for the many hours spent on drafting the maps and figures;and Karen Ruddell and Sheila Finch for repetitively typing the many revisions to this manuscript. i i 1 TABLE OF CONTENTS ABSTRACT PREFACE. ACKNOWLEDGEMENTS TABLE of CONTENTS LIST of FIGURES and TABLES INTRODUCTION .. PHYSICAL SETTING SURFICIAL GEOLOGY MATERIALS and METHOD of INVESTIGATION DISCUSSION landforms Glacial Processes Fluvial Processes Mass Movement Geologic Hazards Flooding . ... Surging Glaciers Mass Movement CONCLUSIONS . RECOMI>lENDAT ION REFERENCES .. iv i 1 .iii iv v 2 5 8 10 10 10 19 22 23 23 26 27 28 33 34 LIST OF FIGURES ANO TABLES Figure 1.location map of the Susitna~Chulitna area 3 Figure 2.Aline drawing of the glacial ice in the Susitna area 11 Figure 3.A line drawing of the landfonns in the Susitna area 12 Figure 4.View to the east of the Susitna Valley 13 Figure 5.Physiographic divisions of the Susitna~Chulitna area.15 Figure 6.View to the south along the Susitna Valley 17 Fi gure 7.Vi ew to the south along the Sus itna River .21 Figure 8.View to the south along Cache Creek Valley 24 Figure 9.A winter Landsat image of the study area 29 Figure 10.A model of the types of depositional landscapes expected to develop beneath ice shee'ts 30 Table 1.Glacial advances in the Cook Inlet Basin 5 Table 2.landsat imagery used in the study.. . .8 Table 3.Physical characteristics of drumlins and fluted topography . • • • . • • . . . • • . . . . . .14 y 1NTRODUCT ION This study uses primarily landsat imagery to interpret the lanrlforms and geologic hazards of the Susitna-Chulitna region.The methods.geologic setting.and a discussion of the conclusions are included in this text,Part 1.The fourteen 1 :125,000 scale maps of landfonns and geologic hazards are contained in an accompanying packet,Part 2. landsat imagery provides a current synoptic view of the earth's surface which is effective 1n smali scale mapping of landfonns and active surface proce~ses.Interpretations based on landsat imagery are especially effec- tive when used in conjuction with stereo aerial photography and ground verification. Repetitive coverage of landsat (presently every eighteen days at image nadir points)records seasonal fluctuation of the earth1s surface under varying lighting conditions enhancing geologic phenomena.Active surficial phenomena.such as avalanches or landslides.and flooding by streams of lowlying areas are recorded by satellite passes during the spring.Also during the spring,the undeveloped vegetation canopy allows observation of the ground surface.provided the snow cover has been removed.The imagery recorded during the summer months exhibits minimal shadows.geobotanical in· d1cators and relatively quiescent surficial processes.During the winter months.variations in surficial expressions are enhanced by the low sun angle (less than gO in Alaska)and by the contrast between the snow cover and dormant vegetation which improves landform interpretations. Active surface processes are often catastrophic.Hazardous areas should be avoid~d or special measures taken to mitigate the environmental risks during planning,or ~tudied more closely. PHYSICAL SETTING The upper Susitna-Chulitna River area is located in southcentral Alaska approximately 90 ~.north of Anchorage (Fig.1).The study generally includes areas below the C10 m (2.000 ft)contour interval between latitude 62°OD'N and Colorado Station along the Alaskan Railroad. The surrounding mcuntains include the Alaska Range to the west and north,and the Talkeetna Mountains to the east.The mountains hinder the northward migration of storms coming off of the Pacific Ocean to the south,causing 74 em.(29 inches)-of precipitation annually (Rieger, 1979)and is the largest amount of precipitation in the state excluding coastal areas. Major rivers within the study area include the Susitna.Yentna, Kahilitna.Chulitna,Tokositna.and Talkeetna.The Susitna River.the dominant stream in the area.drains southward into Cook Inlet.Glaciers including the Da11.Yentna,Kahiltna.Kanikula.Tokositna.Ruth and Eldridge are located in the Alaska Range at the headwaters of rivers and several subordinate tributaries. The landscape generally slopes south from 600 m to 60 m elevations. Numerous north-south trending lakes.swamps and low relief ridges occur on the valley floor.Deciduous and coniferous vegetation grow on the low-relief ridges.Host of the present topography has resulted from glacial,glaciofluvial and fluvial processes. The region is sparsely populated with only one town and several unincorporated settlements (Fig.1).Transportation routes include the •Measurements from the U.S.Weather Service station in Talkeetna.Alaska. 2 , " ,, > (• 3 ( ....o co Parks Highway and :'he Alaska Railroad to the east.A secondary road to Petersville traverses the central portion of the area.Some agricul- tural.timber harvesting.and mining enterprises are centered around Talkeetna.except for lode and placer mining which is concentrated northwest of Talkeetna near the Alaska Range.especially in the Cache Creek area.The minerals or elements being mined include mclybdenum. copper,chromium.gold,uranium,platiunum.tin.coal and thorium (Reed and other·s.1978). 4 SU.F\CIAl GEOLOGY The surfac;a1 geology of the Susitna-Chulitna River area has been dominated by glaciation.This area is a trough into which mountain glaciers and drainages from the surrounding Alaska Range,Talkeetna, Chugach,Kenai and Aleutian Mountains are funneled (Coulter and others, 1965). At least six glacial advances have altered the landscape in the Coo<Inlet basin.(Table 1) Table 1.Glacial advances in the Cook Inlet Basin. Glaciation Sources Alaskan 200-4800 years a90 1 (Nelson and Reed 1978) Naptowne 6.000-30.000 years a90 1 (Pewe 1975) Knik 38,000-65,0002 years ago {i\arlstrom.1964) Eklutna 25,000 1-110,0002 years ago (Karlstn~.1964) Caribou Hills began retreat 155,000-190,000 2 years ago, (Karlstrem.1964) Mt.Susitna pre-Il1onian (Karlstrom.1964) The Ht.5usitna glaciation is the oldest and most extensive glacial advance documented in the Cook.Inlet basin by Karlstrom (1964)and Nelson and Reed (1978).Each successive glaciation was less e'(tensive. T~e Mt.Susitna.Caribou Hills and Eklutna Glaciations completely filled the basin.but during the Knik and Naptowne Glaciations coalescing 1 Carbon-l4 date 2 Boulder count date (estimated) 5 glacial lobes in valleys did not completely fill the basin (Nelson and Reed,1978).The Alaskan Glaciation was generally confined to narrow mountain valleys where end moraines were often deposited at the confluence with broader valleys. The Susitna-Chulitna River a:-ea contains landfonns which resulted from glacial.fluvial.lacustrine.periglacial and paludal processes. During Pleistocene glacial advJnces bedrock was scoured and debris was transported and de~osited by the glaciers and streams.Most of the present topography on the valley floors resulted from the Eklutna, Naptowne,and Alaska glaciations (NelsQll and Reed,1978~. Througho~t the Susitna~Chulitna area the Naptcwne advance left l~w. elongated ridges of ice-molded glacial drift.Streams,flowing along and from margins of the glaciers,scoured channels into the drift and bedrock.Complex ice-disintegration terrain resulted from stagnant ice conditions along the east and west sides of the main valley (Fig.1). The mouth of several valleys were blocked by glaciers.damming the drainages and creating glacier-dammed lakes.Evidence of these lakes are fluviolacustrine deposits in the valleys of Cache,Alder.Peters, Canyon,Granite and Dutch Creek (Nelson and Reed,1978). After recession of the glaciers.glacial drift,which covered the va 11 ey floors.trapped surface wa ter in depress ions or bedrock bas i liS and forming elongated lakes or bogs.Many of these depressions have no obv~ous drainage outlets. Streams reworked the drift on the valley floors during interglacial periods after the Naptowne Glaciation.Modern floodplains were estab- 1 ished by incision of streams through glacial drift and Tertiary 6 sedimentary rocks.Modern streams are generally braided near their headwaters and sediment laden.Broader floodplains possess oxbow lakes. meander scars.and backwash swamps. Landforms and deposits.resulting from periglacial activity and mass movement.occur along t~e mar~i~s of broad valleys and on the floors of narrow valleys.Thes~featu,'es include talus,landslide scars.avalanche chutes and deposits.and roc~glaciers, 7 MATERIALS AND METHOD OF INVESTIGATION The investigation utilized multidate l~"dsat imagery,color- infrared aerial photography.USGS topographic maps and aerial/ground verification procedures. Each of the 1:250.000 scale USGS topographic maps were divided into seven sections and enlarged to a scale of 1:125.000.Each section covered an area equivalent to four adjacent 1:63,360 scale topographic quadrangles (Plates 1-14).The investigation resulted in the compilation of fourteen geologic maps of the area.Seven of the maps are of landforms (Plates 1-7)and seven of geol09ic hazards (Plates 8-14). landsat imagery.path 76.row 16.was used as both a map base and an interpretation medium (Table 2).Seasonal imagery at the scale of 1:250.000 was utilized throughout the study.A special color enhance- ment of a summer image was enlarged to a scale of 1:125.000. Table 2.landsat imagery used in the study. Scene Number flate COlTJIlents 30537-20443 8/24/79 Color scene used for enlargements 1104-20565 11/4/72 a 6 W(alack and White) 30339-20460 2/7/79 a 6 W 1266-20572 4/15/73 a 6 W 249S-20332 5/31/76 Color 5793-19385 6/20/77 a 6 W 30483-20444 7/1/79 Color 2531-20322 716/76 a 6 W 8 NASA 1976 and 1977 aer1al photo9raphy at the scale of 1 :120,000 with ~o\'~"drd lap to support stereo viewing.was used in conjunction with the landsat imagery throughout most of the investigation.The photography which has a higher resolution than the landsat imagery, aided the identification of mapped features. Aerial and ground verification was conducted late in the summer of 1979.utilizing both fixed~wlng aircraft and a ground vehicle.The verification was conducted ~Ul '1 that areas could be studied frJm both the air and ground (where possible)often during the same day. 9 DISCUSSION landforms Landforms of the area were formed by glacial.fluvial and mass- movement processes (Plates 1-7).The glacial landforms are the dominant features. Glacial Processes The Naptowne Glaciation completely covered the valley floor as far as 40 km.south of the study area (Nelson and Reed.1978).The resulting topography is dominated by drumlins·and drumlinized terrain on valley floors.Ice-disintegration features along margins of the valleys (Fig. 2 &3)resulted from stagnant glacial ice and meltwater channels.Till has been fonned into fluted ridges beneath the :;outh flowing glacial ice forming drumlins.rock drumlins and scoured bedrock to the north (Fig.3). These landforms are generally aligned along a north/south axis and grade into each ot.her.The ridges are mostly till.Outwash sand and gravel do comprise some ridges but usually occur on the flanks of till ridges. Drumlins and fluted till ridges are better drained than the surrounding lower landscape.providing a healthy environment for vegetation (Fig.4). The flat.low terrain is poorly drained and typically includes bogs.marshes and swamps.Poor drainage is a result of low a gradient and the impermeable till which blanket on the valley floor.Discon- tinuous permafrost is suspected in swampy areas. *Many of the drumlins"in the study area should possibly be called drumlinolds (term used by Prest.1969.and others).They ha~e the classic drumlin shape but very low relief.However.for simplicity the term "drumlin"will be used.There are a few distinctive drumlins (rock drumlins?)in the northern portion of the study area (Fig.6) 10 I \\ -, ~~ ~\ -, ~---.,..."".-::-~'"--'.-, ,-,.................." (j!! 1_-] "-.~'2._~..?....~~.'(...--- -;. .I&L -- --,r;-I- .'" ~ ,/ /'•1/,,.-;, -1' Flgur'e 2 Aline drawing of glacial ice in the Susi tna Valley.Note the stagnant 1ce terra 1n and me 1twa ter channe1s (1)along the wes Lern border of the glacier and 5ubgldcial-1Ilterglacial drainage chdnnels (2). Figure 3 N I l "'4".1""..•;t....I~,10.,._~_._ If "f~!,.gr"~~~~~ilVt"(U.5:.tn."0:;•••_ A line drawing of the landforms in the Susitna Valley after the recession of glacial ice.The drumlinized topography (1)with standing water in the intervening troughs.meltwater channels (2).stagnant ice terrain (at the base of the slope).incised stream (3)(remnant subglacial drainage channels) and floodplains are all evident in the valley. ~ ~ Figure 4.Vie\1 to the east acrosS the Susitna Valley north of Talkeetna.well-drained druml;nized topograrhy or fluted till ridges have trees growing on their surface.intervening areas have low vegetation and standing water.Photograph by T.George,1979. The Susitna-Chulitna Basin was divided into five physiographic zones (Fig.5)based upon the geometry of the drumlins and fluted topography.The size of larger and more clearly defined drumlins and ridges were crudely measured (Table 3). Table 3.Physical characteristics of drumlins and fluted topography. Area Length Width Height+DOIni nant fom (Fi g.5) 1.<0.3 km <100m <50 ft.druml i ns lb 1-2 km <~00m <50 ft.druml ins &fl uted ridges Ie <1 km <200m ...50 ft.drumlins several km <20()n <5C ft.fluted ridl"es 2 '6 km <300m <50 ft.coalescing drumlins 3 1-1 1/2 km I :"m <100 ft.drumlins grading to rock drlJlll ins and scoured bedrock 4.<4 k..<100m <50 ft.coalescing drumlins 4b <6 km <300m <50 ft.fluted ridges 4e 1-3 km <200m <50 ft.druml ins 5 No streamlined forms +Estimated Zone 1 contains three sections (Fig.5 and Table 3).Zone la is dominated by broad,flat,poorly~drained terrain with a few, small,aiscrete drumlins of low r!lief.To the north lb,the landscape qrades into terrain with more elongated low·relief drumlins and fluted topograph:l.In the northern·most zone.lc.drlJTllins coalesce into wider fluted ridges;the area of the poorly·drained terrain between ridges decreases substantially. 14 • I·igure 5.Physiographic divisions of the Susitna-Chul itna area,based on geometry of drumlins and fluted topography (see Table 3). Cross hatched areas are zones composed of ice disintegration features.Map hase;s 1:1.000,000 aeronautical charts.North is up. 15 Surface forms,glaciolf1uvia1 deposits and deciduous vegetation extending thru zone 1 from Swan lake south along Moore and Trapper Creeks indicates the presence of a former glacial-outwash channel (Plate 2).Thi~channel is relatively low.has a gentle gradient and is locally bounded by scarps. Zone 2 which lies west of zone 1 (Fig.5)consists of fluted ridges and a relatively large number of coalescing drumlins.The shape and north/south aligrrnent of the fluting are more irregular and likely result from the conf1u~nce of glaciers from the west with the main glacier in the Susitna Valley.In zone 2 poorly-drained terrain is less extensive than zone 1. Zone 3 is situated north of zone 1 and 2 and closer to glacia1- source areas (Fig.5).Included in zone 3 are distinct drumlins,rock drumlins,and fluted topography (Fig.6).Flat.poorly-drained terrain, has limited ext~nt this area.tends to be segmented,and is confined to narrow troughs. Zone 4 is located along the western border of the study area in narrow mountain valleys and 1s subdivided into three sections;4a,4b and 4c (Fig.5).The landscape has been overrun by tributary glaciers as well as the main glacier.The dominant landforms located on valley floors and mountain flanks are drumlins,coalescing drumlins,and fluted topography.Generally,the intervening troughs are narrower than in previously discussed zones.Many do not trap surface-water runoff. Portions of the area have bedrock at shallow depths.The broad flood- plain of the Yentna River cuts through the drumlinized terrain.Zone 4a ;s situated on sloping mountain flanks.landforms include less discrete drumlins that coalesce into fluted ridges.Zone 4b encompassed a 16 ~ -~ Figure 6.View to the south along the Susitna Valley from in the vicinity of Honolulu.Twu drumlins (arrows)and druml inize'1 landforms are evident.Photograph by the author,1979. gently sloping upland.Dominant landfonns include long.fluted ridges and few clearly-defined rtrumlins.The flat,poorly-drained areas dominate intervening areas between ridges.Zone 4c contains the most clearly defined drumlins 1n the study area with few fluted ridg~s.Many of the intervening troughs do not appear to trap surface water. Zone (S)is located in the southwest quarter of the study area.It ;s dominated by floodplains and till.The till has no streamlined fonr.s and is likely a medial moraine.Many lakes and ponds are concentrated in the area,few with obvious outlets. In the cross-hatched area along the eastern and western margins. (Fig.S).the melting of stagnant ice resulted in ice-disintegration fea tures.Th'!landforms cons is t of hUlTl11ock,y ridges cOOIposed of ti 11 and glaciofluvial deposits.Thp.till is interbedded with stratified sand and gravel.Folding and faulting due to melting of buried glacial ice is evident in some of the sand layers.The ridges are vegetated with coniferous and deciduous trees.dense alder and willow.and patches of grassy meadows.In the basins between the ridges are many streams. ponds and wetlands. Glaciofluvial landforms such as outwash fans.eskers and crevasse fillings resulted from stagnant-ice conditions and glacial meltwater. These landfonns are evident throughout the valley floor.especially along its margins in ttle vicinity of Talkeetna and along fonner melt- water channels.landforms on the mountain slope and vailey floor east of Talkeetna includes a complex of these glaciofluvial features inter- mixed with a lateral moraine.In ttle vicin~ty of Amber lake there is a complex of probable eskers.Generally.many of the intervening troughs 18 • in the drumlinized terrain likely were melt-water passageways during recession of the glacial ice,as indicated by glaciofluvial deposits on the flanks of drumlins and till ridges.Areas where no distinct moraines and glaciofluvial landforms could be mapped were grouped together as an ice-disintegration complex.Because the glaciofluvial landforms are composed of sand and gravel,they are well-drained and are good sources of construction materials. Till of lateral,recessional.and terminal moraines overlay and intermix with the drift of the drumlinized terrain.Sane of the lower mountain slop~s bear lateral moraines that were not destroyed during ice disintegration or by post glacial.fluvial and mass-movement processes. Till from a large lateral moraine is evident on the mountain slopes east of Talkeetna intermixed with ice-disintegration deposits. Recessional moraines are evident in the vicinity of Swan Lake and in the southern part of the study area (Plate 2).These moraines were deposited by former glaciers flowing out of the valleys of the Tokositna and Ruth Glacier valley and Kahlitna Glaciers,respectively.during the late Naptowne or Alaskan Glaciation.Many of these moraines have been eroded and segmented by glacial meltwater.Nelson and Reed (1978) mapped several other recession moraines.especially in the vicinity of Schneider Lake.Several anamalous east-west drainages in this area may indicate the presence of recessional moraines. Fluvial Processes Superimposed on and incised into glacial deposits are floodplain and terrace deposits originating after recession of the Naptowne Glaci- ation.Floodplain deposits are composed of stratified gravel.sand and 19 s;1t,and are likely sources of construction materials.Floodplain surfaces are gently sloping Jnd well drained,providing excellent po- tential sites for development,although they are susceptible to flooding. Floodplains are divided into active,partly or infrequently active. and abandoned (Fig.7).Active floodplain surfaces are subject to annual seasonal flooding and include existing stream channels.Season- ally active channels,oxbow lakes,ponds and wetlands typically occur on active floodplains.Partly or infrequently active floodplains are not necessarily inundated by seasonal flooding but may be susceptible to flooding due to their proximity next to active channels and relatively low height above modern streams.Portions of these floodplains may be flOOded by tributary streams.Abandoned floodplains or terraces are considered least likely to be affected by high~water conditions due to their location and height above stream channels. Small abandoned stream channels are intermixed with the glacial landforms;they are typically not related to present drainages but are a result of drainages established during glacier recession,stream piracy. or channel migrations.These channels commonly contain swamps.bogs or marshes. Alluvial fans develop where the mountain streams become unconfined and spread out.These landforms are composed of alluvial gravel.sand. and silt.The coarser material being near the apex.Fans in the study area are vegetated and their streams are typically entrenched and braided.A few alluvial fans are located in the Talkeetna Mount~ins but most are in the Alaska Range.The most extensive fans are along the Ventna River.In several nariOW mountain-valleys alluvial fans are 20 N Fit]u'"e 7,View to the south along the Susitna River frorl in the vicinity of Sherman.Floodplain map units are evirlent:active (fa).partly or infrequently active (f1L and abandoned ((2)' Photo"raph by T.George.1979. • partially blocking the valley.forcing stream channels against the opposite valley wall. Mass Movement Lower mountain slopes and narrow valley floors contain mass- movement landforms,including talus slopes.avalanche chutes.land- slides scars,and rock glaciers.Talus slopes include steep bedrock surfaces.cones and fans.Talus is an accumulation of angular rock fragments formed by frost weathering of bedroc"k and transported down- slope by falling tumbling and rolling primarily during periods of spring thaw.Avalanche chutes are present on steep mountain slopes but are concentrated in the northwestern part of the study area.Chutes are cut or modified by rapidly moving masses of snow,ice.rock and soil. Tongues of boulders or rock debris typically accumulate at the bottom of the chutes near the base of the valley walls.Extensively affected areas include Coffee River,Hidden R~'fer and Ohio Creek valleys in the Alaska Range and in the vicinity of Indian bQr.Hurricane Gulch.Sheep Creek and Kashwitna River valleys in the Talkeetna Mountains.Rock glaciers are located on many floors of narrow mountain valleys 1.,"~e study area.Over 100 active and inactive rock glaciers were mapped by Nelson and Reed (1978)on the Talkeetna Quadrangle.These landforms are developed from talus and other mass-wasting debris which form tongues of rock fragments moving slowly downslope.In some localities active rock glaciers are overridi~g inactive ones. 22 .I Geologic Hazards The geologic hazards (Plates 8-14)are active surface processes that alter the landscape in a potentially catastrophic manner.The alteration may be short or long duration. The geologic hazards in the study area include flooding.surging glaciers.and mass movement.The map units a,.,.~derivc.d from the pre- viously mapped landforms.multidate Landsat imagery.and pertinent ~iteratuf-e. Flooding Flooding is a seasonal event in many river valleys affecting the stream channels and associated floodplains.Certain portions of flood- plains are more frequently affected by high-water conditions than others. Proximity,relative heights and vegetation were used to distinguish the relative frequency of flooding on floodplains. Floodplains are divided into two divisions.primary and secondary, based on their sucept1b111ty to flooding (Plates 8-14).The pr1mary floodplains are subject to seasonal flooding,standing water and channel ~igrations.This unit includes existing stream channels.Secondary floodplains are surfaces subject to infreq~ent flooding due to unusually high water-levels.Portions of these floodplains may be annually flooded by tributary streams. Most of the rivers in the study area have developed floodplains confined by scarps with terraces (Fig.8).The scarps will confine floodwaters but are susceptible to erosion.Older abandoned floodplains 23 • '" Figure G.View to the south along Cache Creek.Valley.Streams.such as Cache Creek are typically incised into the lanrlscape.Photograph by T.George,1979. or terraces are not typically affected by flood conditions due to their heights above streams. Standing water is a wide spread condition encountered in the study area.Many low-lying areas trap and retain water,and typically develop into a wetland.The map units (Plates 9.10 &13)encompass areas where a large portion of the terrain is wet,especially south of the Petersville Road.North of the Petersville Road standing water conditions decrease steadily.The author observed several areas of standing water along the Parks Highway in early winter,1979,south of the Parks Highway--Chulitna River crossing.The standing water was not present in these forested areas during the summer field season indicating periods of flooding are short and seasonal.The cause of this flooding is not known. Flooding is not always a function of surface runoff but is occasion- ally affected by unusual events including outburst floods.aufeis and torrential floods.Outburst floods are caused by the draining of glacier-dammed lakes.In many areas throughout Alaska outburst floods occur annually and usually by late August (Post and Mayo,1971).These lakes are generally located along the margins of glaciers.although some are located be~eath or within them.These lakes drain when a pa';ageway is opened through the ice dam.Glacier-dammed lakes which affect the study area are identified along the Eldridge.Ruth.Tokositna.Kahiltna. Yentna and West Fork Glaciers (Post.1971).Primary floodplains of streams draining ice-dammed lakes are affected by periodic outburst floods.There is no evidence that outburst flooding in the study area is an annual event. 25 Aufeis is a local floodplains phenomenon in high and alpine middle- latitudes.Thick sheets of surface-ice develop on floodplains by the freezing of thin sheets of water during low.winter temperatures. resulting in flooding beyond the stream r.hannel.Aufeis presents diffi- cult engineering problems with respect to buildings.highway or other structures.locations where icings occur are best avoided.Most braided streams in the study area are susceptible to aufeis.In the stlldy area aufeis conditions were not as severe as areas north of the Alaska Range. Alluvial fans are susceptible to torrential floods and debris- flows.The alluvial fans in the study area are located in the western mountainous regions (Plates 10. 11.13 &14).Most of the fans are vegetated indicating their surfaces are stable.The main stream channel on many of the fans are entrenched.confining ~he effects of flooding and debris flows to the channel.However channels are susceptible to back-filling and relocation.The portion of the fan within 30 0 of the mediai radial line is thought to be the most active area (Bull.1964). Alluvial fans are usually an excellent source of groundwater and con- struction materials but typically poor building sites. Surging Glaciers Periodically surging glaciers which could affect streams in the study area include the Yentna.lacuna Glaciers and the two northeast tributary glaciers of the Eldridge Glacier.The angular crenulations of debris bands on the surface of these glaciers near their termini is indicative of a surge history (Post.1960).The Tokositna Glacier may possibly be subject to surges,although the geometry of the debris bands indicates pulsing rather than surging (Mayo.1976). 26 The hazards of surging glaciers include glacial encroachment, flooding and proglacial sedimentation.Flooding and sedimentiltion wi 11 affect the primary f",oodplains of the respective glaciers and some secondary floodplains. Mass Movement Steep mounta!nous slopes and parts of valley floors are susceptible to mass movement hazards.These hazards include avalanche and land- slides,falling rock.and debris flows typically associated with talu~ slopes.Most mass movement hazards are especially active during periods of spring thaw.The hazards associated with mass movement are located in mountainous regions throughout the study area (Plates 8-14).The Alaska Range along the northern extremity of the study area is parti- cularly susceptible to mass movement. 27 CONCLUSIONS Most of the existing morphology ,f the Suslt~a-Chul;tna River area resulted from Pleistocene glacial advances.The north/south alignment of the druml1n~led terrain,drumlins (often with low profiles)ar.d scoured bedrock (Fig.9)indicate daminent glacial sources were the Alaska Range to the north and west ·,neluding areas in the vicinity of Susitna and West Fork Glaciers.Secondary sources were the Talkeetna Mountains to the east.The confluence of the glaciers from their respective directions has affected the alignment of the landforms especially around the margins of the Susitna-Chulitna valley. The drumlinized ground moraine and intervening troughs have been streamlined by the ice movement but few druml ins fully develop.In previous studies the lack of drumlin development has been attributed to unsuitable basal ice conditions (Hoppe,1957).or dilatance related to deformation and load (Smalley,1968). The drumlinized topography is most evident SOU ....1 of the Tokositna River.There,intervening troughs are poorly drained and usually with standing water.The presence of glaciofluvial deposits on the flanks of several of the drumlinized ridges and beneath the swamps in the trouahs indicate mel bater channels once flowed in many of the troughs. At least one meltwater channel extended trru the study area from Swan lake south and apparently splayed into several Channels south of the Petersville road.The Susitna River was probably an ac~ive melt- water channel. The Tokositna River appears to make a transition in the formation of landforms and hence basal-ice conditions 111 the once overlying 28 • N ~ Figure 9.A winter Landsat image of the stur1y area sho.....ing the al ignment of rlr~'ml inlled terrain all the valley floor (1)and scoured bedrock in the mountainous regions.(2)Scene #30339-20460. February,1')79. • .......,... glacier.Drumlinized till and glaciofluvial deposits are extensive south of the river.The extent of glaciofluvial deposits suggests that water either was prevalent beneath the glacier in this zone or flowed through troughs between till ridges beyond the glacial ice durin!]its recession.If the glaciofluvial deposits are as extr~nsive as the author suspects,then the rapid dissolution of glacial ice is likely. The modeling of depositional landscapes (Fig.lO)by Sugden and, John (1976).describes the Susitna-Chulitna area with some modification. The study area includes the erosion-transition zone.active zone and transition-wastage lone.Drumlinized ridges and drumlins are intermixed. The brea~between the fluted ground moraine and drumlinized ridges occurs in the vicinity of the Tokositna River.North of the river the glacier was constrained between relatively narrow mountain valley walls and fluted ground moraine is prevalent.South of the river the valley floor .........,.~.....,..-~-i.....,...1 '",,,••,_0" ~~!t ..........··,.·· (1/1/QIJ -:~"..-=::::~=····''-r-----'.l~i .i I I oCJ .!-.<~--.;.,.,-I I 000.'""-c...-,,. :II I Q 0 'i:.-;,."'.. -~\I <£70 g"l~",>':,~~.: i \[?""I!..''": \.t qa ......'\~-~.c Co "._ _I . \Dt'...J·.,..-. 1 '"--i:.?,_....--<.-,>.-~.......... \csl);....,~.:'"''''''-:c:'.........{)~..;II "..............................""";'''-.....",,-..;......~.....,:,.....-"~ Figure 10.A model of the types of depositional landscapes expected to develop beneath part of the periphery of a mid-latitude Pleistocene ice sheet at.or just after.the phase of maximum glaciation.!lot all of these landscapes will develop contemporaneously,and the landscape type is determined above all by the character of the ice above a site when rapid dissolution sets in. :;0 I broadens significantly and till lodgement and streamling occur.ihe change from the active zone ~o the transition-wastage zone occurs south of Amber Lake.Drumlins,eskers and possible Rogen mor~ines are evident in this area especially in the vicinity of Trapper Lake.The wastage zone,associated with the ice terminus occurs south of the study area. Fluvial processes h~ve d~stroyed many of the landforms associated with this ~one. Active surfacial processes are often catastrophic and hence called geologic hazards.Detectable hazards in the study area include flooding, surging glaciers,and mass movement.Flooding which results from surface runoff occurs on low-lying floodplains and troughs.Hazards aassociated with glaciers susceptible to surging include glacial encroachment, flooding and proglacial sedimentation of most river vaileys in the area. Local flooding results from unusual events including the bursting of glacier-dalJllled lakes,development of aufeis and torrential floods.Mass movement including avalanche,landslides,rock falls and debris flow affect lower mountain-slopes and the margins of valley floors. This study on the Susitna-Chulitna River Basin is intended to provide a regional overview of the area.The study of landforms provides a basic level of information from which octive surficial processes can be studied and the distribution of surficial deposits can be inferred. landsat imagery and small scale aerial photography have shown to "Je excellent sour=es of regional data.The results of this investigation are intended to provide a data source for regional planning and hp.lp define natural constraints for areas.The maps should not be used for local planning. 31 Registration of mapped landforms to USGS topographic maps involve map unit boundary shifts as much as 1/2 mile.This shift is attributable to geometric distortion inherent in Landsat data and is evident in mountainous regions along the margins of the study area. 32 RECOIt4ENDATIDN The regional maps from this study are intended to aid regional plann~ng,target potential areas.eliminate areas with few attributes, provide bench mark data for impact studies and direct more detailed studies.More detailed studies at a future date,may be required in critical areas defined by planning needs. The following phenomena may require more extensive investigation in the future: (1)secondary floodplains described under geologic hazards; (2)early winter standing-water in forested areaSi (3)torrential floods on alluvial fansi (4)satellite monitoring of glacier-dammed lakes (Hiller,1979); and (5)larger scale maps of landslide and avalanche lones. Consideration in the futl~re may be given to the preparation of slope, vegetation and construction material maps. 33 • REFERENCES Bull,W.G••1964.Geomorphology of segmented alluvial fans in western Fresno County,California:U.S.Geel.Surv.Prof.Paper 352-E.pp. 89-129. Caulter.H.Wo,Pewe.T.L.t Hopkins.D.M.,~ahrnaftig.C.•K~rlstrom. T.N.V.•and Williams.J.R.•1965.Map showing extent of glaciations in Alaska:U.S.Geel.Surv.I11sc.Geo\.Invest.rtap 1-415. Fairbridge.R.W••1968.The encyclopedia of geomorphology.Oawden. Hutchinson and Ross.Inc .•Straudsburg,Penn .•1295 pp. Flint,R.F.•1971.Glacial and Quaternary Geology,Hiley.Hew York. (892 pp). Hoppe,G.•1957.Glacial morphology and inland ice recession in northern Sweden.Ge09r.Annlr.41 p.193-212. Karlstrom.T.N.\t ••1964.Quaternary geology of the Kenai Lowland and glacial history of Cook Inlet region.Alaska:U.S.Geol.Surv. Prof.Paper 443.69 pp. "ayo.l.Rot 1976.Identification of unstable 91aciers intermediate between normal and surging glaciers:Proceedings of the inter- national workshop on mechanism of glacier variations.Aluma-Ata and Moscow.U.S.S.R .•pp.133-135. Miller.J.M.•1979.A Satellite quick-look system for ."laska:A Report to the Eleventh legislature of the State of Alaska.Northern Remote Sensing laboratory.Geophysical Institute.University of Alaska.Fairbanks.Alaska.pp.C3-C5. Nelson.S.W.•and Reed.B.l..1978.Surficial deposits map of the Talkeetna quadrangle.Alaska:U.S.Geo1.Surv .•Misc.Field Studies Map,MF87OJ.Scale 1 :250.000. Pewe.T.l .•1975.Quaternary geology of Alaska:U.S.Geol.Surv., Prof.Paper 835.145 pp. Post.A.•1969.Distribution of surging glaciers in western north America:Journal of Glaciolo9Y,V.8.No.53,pp.229-240. Post.A.and Mayo.l.R.•1971.Glacier damned lakes end outburst floods in Alaska:U.S.Geol.Surv.Hydrologic Investigations Atlas HA-455. Prest.V.K.,1968.Nomenclature of moraines ~,d ice-flow features as applied to the glacial map of CAnada.Geol.Surv.Pap.Can.67- 57 (32 pp). Prest.V.K.•1969.Retreat of Wisconsin and recent ice in North America.Geol.Surv.Can.Hap.1257A. 34 Prest,V.K.,et al.1968.Glacia1 map of Canada.Scale 1:5 million. Geol.Sur •.Can.Map l253A. Reed,B.L.,Nelson,S.W.•Curtin,G.C.,and Singer,D.A.,1978. Mineral resource map of the Talkeetna Quadrangle,Alaska:U.S. Geol.Surv.Misc.Field Studies Map MF870-0.scale 1 :250.000. Rieger,S.,Schoephorster,D.B.,and Furbush,C.E.,1979.Exploratory soil survey of Alaska,U.S.Dept.of Agriculture,Soil Conservation Service,213 pp. Smalley,I.J.and Unwin,D.J.,The fonnation and shape of drlJlllins and their distribution and orientation in drumlin fields:Journal of Glaciology.V.7.No.51.pp.337-390. Sugden,D.E.•and John,B.S.,1976.Glacier~and landscape,Edward Arnold Ltd.,London,England,376 pp. 35 SUSITNA BASIN PLANNING BACKGROUND REPORT SurfiCial Geology of the SUSz~na-Chulz~na River Area;Alaska Part 2:Maps KENNf:SONG.DEAN .VORTHE.RNREMOTE SENSING LABORATORY GEOPHYSICAL INSTITUTE UNIVERSITY OF ALASKA FAIRBANKS,ALASKA preparedf.. LAND AND RESOURCE PLANNING SECTION DIVISION OF RESEARCH AND DEVELOPMENT ALASKA DEPARTMENT OF NATURAL RESOURCES MARCH,I980 ~_""._~"_.....MY -----------_.- PHYSIOGRAPHY OF THE UPPER SUSITNA-CHUUTNA RIVER AREA,ALASKA by KENNESON Go OEAN 1110 <8> Low Iy""ll bIoino 00Ildul:....'0 U_... ..-IIOIW". %."Sutrta..-int _•• Plate I EXI'1.AH...TIOH _..........T..,._.otl__tl«l by I~I bI·_...,.....abP_ b .........t«lroc:, -"'«1 wiIl'I ....1l.«I ""'"""''''''PI.bP__'«I ••_loooo<ltl>lh SIoI>v"Il.,_._Illy __•,..,._ ....t....._••dia INn _....,1. -.g..,..0'bt....-vol . 8.-........'.0-",- • a o, ,...,._...itI ............ obs...o.c'''''_9Ia<iol"",-,- ~""""",,,_1 __.0..",_,_ ....£tIIl __ ml LI _G__ GI.,>tIat,h ,£~\Suopec,""_""_th_ondtih DnImIIno,,,,,,....,.....y ....,......0'tirl~01 ,ilcitl at;h 'tll.mI.""w,th "",,"y cIt"""-:l Iowlying_...d'1Qo.,........,.do,,"""'PIt. •Eoh, er:>.Incl1nd ....dNtnl;.-. ev·c._rill ..o ~~:"..:.::.--,in __ / " "..............w..:_,...",_/o<tlwo--=*.__.,,,,••,,,,_ -.o;din"",OlI«''''' 141°lII'W ---..,......----,'"12°30'" " .o "b ~_IY"'9_fOI'OuC".'O"_1I..,,_...... X.SUtlHd..-...,....... ......._~ op ""........_1..._0.._,_ ....£"""--....~a'_ G,_ Gt«""tt ,~::,Su-'od .~_...._.-......""dr." ....................._laNIoI.,..""'.. U Oobr ..,.....,iftt I,,,,,,."rotot. At AoU;lIiI<itr..-.. '"'ltr'Tod I>ot.ontIar¥ --.,,1"",..1,... .,~.v-n~ ,.Act I'tootkllI.. "P ly"'....._,lyac,...,'-Ipla.. '1 ~r.....".....,.-_. On,oml'od ,_apfty _.,t '.......,t p .."h ...'_•...,......_ly",__Iy;",_ lU<h.""..,.._<_.,...,-...._- e.-hlI""",0.....'_0'ooa,.._,...._....,_......... I A~r.d_......_-",,_aru ,_~._..~...'...od_-....,,"---,..- ., ~., Plate 2 PHYSIOGRAPHY OF THE UPPER SUSITNA-CHULITNA RIVER AREA,ALASKA "I<ENNESON G.DEAN 1980 ~ ~'-"'"r_..~.""""tIIM*..od by "nD'I..-..."".....__ b ........._otk •-,-lod ..;,-"'c."w'"_""",.-. _k_,....,__dc>Ill Slop""r.,_·_llIv wMll _Uon .,...,....",,-,.dil.__.."...,",,"" -..""..01_.........a 8ro1ll.olleylloof G C;.......,.I'to,_ GIoe'" t Ac;'_~II'......"". Db Su..-:t""_....., ....l .....~"".1'",..0<>._,...._0..,_,... ~E"ll ... ""u._morolne G nd ..... (;I "'j ... D<uwIl,ni.."'_~y .-...,01 riclgeo 01 ~cki"It>,_."",..;1t>_lyd'_10 ..1""'_, II.....<lil.in\I9.._~. t.b.~'::'-_"Oidl3:~..,-:'I;l~;':::._,in __ ~--t ·R..........."'_..........:~l>tpoi"'I_~gIKlott.d"""""__1<l __ -*lin ................~ Low 'vIAgMsins _ioo.",''llIIint _'-wltl< .1 SulPlCllt""'IAg ...u< v otI s..-''''_glooIl 00._.-..... "lI "ou_'...._0.._1.... ....(1'01..--.0....u,__ ...0 1'01 _<l a..,",." """-.,AI1""iIoIlon.._"......_..,.Act"'~ "Portly or ;"trwl.-,Iy "''''.'1oodpIoon '2'-~--, lOwly...bHins •...-...'o,,_ ....1 _'.. X.Su ,"_"'9_or 0n0mI '-_y ...........01 ......,1....,...;""'_ty<l._-ty"'-.,;-;...,'.....-.-.,..c::>1",jI,,__1noict> 0'~-:'I~~t=or _.,.._OUfw_._:. I Ih............or -..........-pCI"",- I",.......~.-_.;,,- _,.d '"""",*,1 ..... .................-_I....,..icl<Iot.I'.. u Doloois ,lrlt I........Io,..,hlod. "I'11001<........... "....'I",...""""""""'" ".' .L .ll.....:::....L__lL-"=""'-""":."J 11°00'W IS 00 00""TALKEETNA ,4,'1,A-2,8"1,8'2 _~_u~~.._. ,--.,.. • o ~o ,..... ,"',:1_fIoooI'............ lib SuOllOCI..__9'000' ...tw"",,C_ OIl ,,".....'_'_ ow 0..,_'_ .....EncI"",,_....l_""",,_ G_"",,_ Gloool ""It (lO'l..ANA'1ON Plate 3 M _,_,0/,.._..lid t>v ,~I til __....,00:1_.... b ......._•..:k •~oo:I ....tIt OCOI'....rock ...=-0.__,..o,_'-~_ ~,__oI1V <nod -.,... lIrod~__0 6<•.-.~..",..,"""_ ......_oltw_...~ /Iroocl"leyl_ Gloc....P1.,_ low ,Viftt .-...._'0 '_I ...r..w .. .::t:.Sutpoc."--"_,or ':~:\s.r-c,.."'._...._tnonReIt ond"t, Dn"","n"od '_OPhv .-m 0'~0' gloc>oId"It 'w.,..pCIOfl/a'_ '-1.....bHi... le..lioitt'ovot _...........,.. I~_a ,_ c.e....tin ... D.."u;"n 01 wo,._,..._...,--t 'A u_"""....;_"""',___-.inf......l_-__,- PHYSIOGRAPHY OF THE UPPER SUSITNA-CHULITNA RIVER AREA.ALASKA 0, KENNESON G.DEAN 1910 <@> ;' 1I:....·w fluYiol u,....:__ ,-........ Gt......,.," .f:",Su.>Kt1d'"lnot '_.~....<l'," On.nIlolo'.1d 'OD09'_Y'ol,OjeO oj......"',!!"'''''''''''·;'''_101<1,__'y",,_ lC*d.....,"'.......~',..1""..- e-t;'I""",O,f'IC ot"'.,.._,..._ ....t et>onneh A......."...."""".,.......b<io'ut 1'_''-_~.__.in......__'-1",_,.._ SfO'o,.:lli.llCG_. ,,t 1 3 .....,"""""-== o r~~""""'" l.o-il ,_"""I"""11vdOI~. Ali R«~gIK>O'f......... ,",...ed tIOuo'I<WY .........~.....IM>d..od••""I.. _x_ "'Aj""'~'.."'_"'_01 I.Act;"11ood ... I,'....lto<...l_l\ooa....lloo<Illlo... 12·~t_........ Mo."'-""• '-E""........,a'...... o o • t l_ty""_...toI'duc....,a ,,_... .,rf..,.wOl.. ..Jt.Sutp«'"''''i'''J-''' v Plate 4 PHYSIOGRAPHY OF THE UPPER SUSITNA-CHULITNA RIVER AREA.ALASKA "KENNESON G.DEAN IUD ~ _-...r.,.01,..._....b.'oll O'I_.I<OU _"""°......_ock•_~od _'"....,...n>do "",er_.bOO."""_,.,.,_low 1lOP'"$Iopo,,,,t......_.11 .........,__ "..,....,e.-••diI..""""_"'~ ........-01_'-B'_~..!I_ GI..... ~,- ,Ac'.........I'..........ob SIIIo>«l.._....... "",......-"""'''001'''''_'...._OU',.... ....E""_....l.'_ '"G""""'...GlKIoI",," ::~::'s..-,""_....,_...............""" Clt\a'<II,,,....__"0/'_01 ....~""h ""od ..,tIl~."'_ .....I.""l_...". b ~.::_"""''''' <;=t~;-::._.,"'_....,........... t R..-_......a.:•._"',,_ _....'-.__.;"lott .....--"'-,.... l_-.cIuo:...'o,,_... ...r.".,,, .:t:.$uIoon ''-''''l -'...- _'1;1',__'" ,,J ..... ~.~!-.\ . -~t::". .., ..................-.d,...."....cI'o.I,.. U 0«0<;,,-.1.....I""".1MIdtI,* AV A",,~....,.......,'ft''" lOwly""l_«>rcIuc_,,,,,_...-,on ...·•.±~,,0I'd...._,.. ,~. ....-.,....""'...,..."'_.._<-r.A<,,,,,,'~:;=':';:::""'_1_,.,-- """'"......,-,....000 0..,_,....E __ l _ G_... GlK>oI"',I, (~::'SotoI>e<t.._"",,~~."',,.,," d,0..-...,.._-"'"n"''"''''''''".........."..,.......0<1 ..."'--...._ -,~...- ",..........,...-.-.b ~.::_ (j ='~,n:.._....-...-....-...............Jl..-",..,..--,__,_ t _"""'-........0<1 __......_.... .'n" T.4.LKEETN.4..4.-5,.4.-6,8-5,8-6 1__U.l.Goooot'<oI_ 1~_.1"" Plate 5 PHYSIOGRAFHY OF THE UPPER SUSITNA-CHUUTNA RIVER AREA.ALASKA "KENNESON Go OEAN 1..0 <@>--M·_r__.""-'__hotin.........--11 ....._.---_--__-~l_~_ ~--.--~---.-.-....--.......a oIIt¥"-r G G......- .~......'-....~--......--...P;t _,___1_ _E""__ 11III.LM_....._",.co--__ d .Gt.eiol.,tI ~~~"s..-...........,h t\l ~f_oI""'"'oI .....dritlin_"'-'._ -,.,~-c!;•Ia.w.n...._.......... • l ....0·1 _ .,.·e.-Mricito ¢'~01 ...,.-.ln_ ~--t R_Ot_.........;_"""',,_"-*110'--1_--.. L_I,"",_C_'"I.1r0llPnt lUrl_w... ..z:.s..-.<•....-.l....-'Of ..- ........A .........._~<1'lu'.. u·o.totlo,_ltint'.-a-..klt IIg.R...k ............. In''''''1>out><Iatv L_Iy;r.g _...lOtr_ ••ff .. .x.s..-,..-int-,.. -_._-----~-lOP'"".-lou_I...._.0.._'__E",,__ .....lA,...._.. G_..... • G...oolClrltt .....i8l '...En~~--.t .A'........'... ..~•.,...,et-w'ool la ....,...l\oodlllOlln • I,p."ly ..."'''-tly 0<'_fIooclpY... '1 .__lloodpl6ltlo---. 011 OnImlinlIea --"y:--.n of ......of 9locW drill Inwonlaea _-"t ~--cti_~__ •E*..($>.,,,_ C'/·G.-tiIIrlcIto".:.=-..::..::_~In _... t ·__...........·_~'-fotorw __In __ -*,In~.,.. v .'~;'" TALKEETNA ,IITNS.C-S,C-6,O-S.0-6 ••__u.s..~-. ,_.eat.,... ". c.-/ Plate !i PHYSIOGRAPHY OF THE UPPER SUSITNA-CHULITNA RIVER AREA,ALASKA., KENNESON 0.DEAN 1110 <8> .'l Moun~r on..b£oftkll:lll by I~I 101·__,r-t_od ".....'-- .·_'-IllloritllocM'1.eatotl<...-._totI<_,ea¥c _low.'" $IoplI\tT......:....oIIy ............,... "lid..,_on •dil.unte "eM."'""_il.____o._..u.vs_.01 ......- ·Oloe...·PII,_ ,AcI_'.m ....... ""'·5u ea._~ ~-",,·Pilllld ..._'_ cow 0..._'_ ....End .........lac _ m •Gtouna ...... d •Ol.....dflll '-X..~\5uIpoctea m'nor .....__...,droh On>mIini.lId 'OP<l9""IlItY"__...ot 'od9I<01 gIo<;ioI ctrih in,.,N.ea .oth -'vd._ _I~"'" <Ii •'"4i1in'''''..Ion-.,.... b.~::iduoI_i_ 0':=-=.":t".:•..........",in __ ~--t ·R__....,_:_.....,_ fomw _inloorr-t...., _Iodin_,... Low lyinljb.......<II'Idueio.'Olt_"9......_-,. .j:.-SJIlIK'....<t......,. .~, _.,a,__'· • a ,,J .....e-a-+i b: ~_,.,""l>eIirtIc~"otr~-_. ..:E..s..-t~W>t ..... v --,I IJ........I....·AIIonclonoclrtt...._ I.Act '-">lo.. 11 1v ...in"-'tlytct....11ooclpII.. 12~~-_. _:.,/T....."- ..........__lar<htidoom.'.. 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In!omd_. v O-"~·CIOO_. ,,J ....., Plate 8 "'_outIjec'.o ou1t>ll"."""". fll'LANAliON "'..........IIoodpIo.in.~=~~'O ....,'"9 ................... o.. o GEOLO'3IC HASUSITNA_CHUUTN;ARDS OF THE"RIVER AREA,ALASKA KENNESON a.DEAN 1910 <8> v TALKEETNA ,IlTNS.A'S,A'6 ,B'S,B'6, ? 0 s.:-v ~.M>joclIO _;O';O;_<I....""'......V_._,;0..","y be-etivo..0'-*__..... D ....._"-"'Iet1IO ........."'_..._...........IelI_.. Q ...,......._...__50 .-_._int ...... ~l_..-;.c,10 ....._1 1nduc>"'lI __'.,1Mxlol-. _................."'_..,'",,",,*..~ ~AI""""1....:"""""'ibIo.o ,orr",riol lloods_......11.-. 1$0°00'W__U.$~-' '*'-.'tISoI ...._tto... ........,.,."'-1_"""""0__flood""._ -""t"M'"........,................,........,-~ ~!~_'10 I*_'lood",,_~_•........._'"0.........'"«1_ ..~-.lI....._._'O,_,... '10 """_"'-. ...,...."ft_••__50..._..-.......,. z o _,__l.n<ho ,•.__. _,"-..'011_....~ EXI't,AHATtoN ptat.9 o., o..... 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