The Alaska Earthquake March 27,1964: Regional Effects
This volume was published as separate chapters A-J
GEOLOGICAL SURVEY PROFESSIONAL PAPER 543 UNITED STATES DEPARTMENT OF THE INTERIOR
STEWART L. UDALL, Secretary
GEOLOGICAL SURVEY William T. Pecora, Director CONTENTS
[Letters designate the separately published chapters]
('1) Slide-induced waves, seiching, and ground fracturing caused by the earthquake of March 27, 1964, at Kenai Lake, Alaska, by David S. McCulloch. (B) Geomorphic effects of the earthquake of March 27, 1964. in the Martin-Bering Rivers area, Alaska, by Samuel J. Tuthill and Wilson M. Laird. (C) Gravity survey and regional geology of the Prince William Sound, epicentral region. Alaska, by J. E. Case, L). F. Barnes, George Plafker, and S. L. Robbins. (D) Geologic effects of the March 1964 earthquake and associated seismic sea waves on Kadiali and nearby islands, Alaska, by George Plafker and Reuben Kachadooria~~. (E) Effects of the earthquake of Marc11 27. 1964, in the Coljl~erRiver Basin area, Alaska, by Oscar J. Ferrians, Jr. (F) Ground breakage and associated effects ill the Cook Inlet area. Alaska, resulting from the JIarch 27, 1964, earthquake, by Helen L. Foster and Thor x. V. Karlstrorn. (G) Surface faults on Montague Island associated with the 1964 Alahka earthquake, by George Plaflter. (13) Erosion and deposition on a beach raised by the 19ki4 earthyuake. Jfontagne Island, Alaska, by 11. J. Kirkby and Anne V. Kirkby. (I) Tectonics d the March 27,1964, Alaska earthquake. by Grorge I'lafker. (J) Effects of the Alaska earbhquake of March 27. 1964, on shore processes and beach ~norphology, by Kirk W. Stanley.
U.S. GOVERNMENT PRINTING OFFICE: 1968 0 298-580
STOLEN FROM RiCHARD D. REGW
THE ALASKA EARTHQUAKE, MARCH 27, 1964: REGIONAL EFFECTS
Effects of the Alaska Earthquake of March 27, 1964 On Shore Processes and Beach Morphology
Bg KIRK W. STANLEY
The efects of tectonic uplift and subsidence along 10,000 miles of shoreline, and the practical meaning of those eflects
GEOLOGICAL SURVEY PROFESSIONAL PAPER 543-5 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary
GEOLOGICAL SURVEY William T. Pecora, Director
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 45 cents (paper cover) THE ALASKA EARTHQUAKE SERIES
The U.S. Geological Survey is publishing the re- sults of its investigation~of the Alaska earthquake I of March 27, 1964, in a series of sin Professional 1 Papers. Professional Paper 543 describes the re- 1 gional effects of the earthquake. Other Professional I Papers in ithe series describe field investigations and reconstruction and the effects of the earthquake on communities, on the hydrologic regimen, and on transportation, utilities, and communications.
I i~
CONTENTS
Page Coastal features and earthquake Introduction -__-__------1 effects -Continued Shorelines of the earthquake-af- Coastal erosion and movement. fected region ------______---2 of material-Continued Coastal features and earthquake Longshore material move- effects -----_-_____------3 ment _ _ _ _ _ - - - _ _ - - _ _ _ _ Beaches--______--______3 Upslope material move- Changes in profile and ment_---_-_-_-_-_-__ gradient ---__---______3 Biologic effects of shoreline Minor beach features- - - .. - 5 changes-.-__.__.___------. Low-water features------6 Fish__-______---_____-__ Modern beach ridges--- - - 7 Shellfish - - - - _ _ _ _ _ ------Wildfowl _ _ - _ - ______- ______Ancient beach ridges--- - - 10 Effects on property and manmade Stream-mouth changes-_----- 10 structures..- - _ _ _ - ______- ______Submergent areas --__-__10 Submergent areas- - --- _____- Uplifted areas--_- - _ - _ - _ - 11 Emergent areas --_--_____-_- Coastal erosion and movement Legal problems --_---______of material ---______-____12 Need for further studies --_-_---_- Erosion ----_--______12 References cited -----__--___-____
ILLUSTRATIONS
FIGURES
Page Page 1. Index map of south-central Alaska showing coast- 9. Photograph of gullying and sloughing caused by lines affected by the earthquake -----_------VI headward stream erosion, Copper River Delta- 2. Diagram illustrating beach feature- - - _ - - ______- 53 10. Photograph of eastern shore of Cook Inlet showing 3. Photograph of sharp break-in-slope on shingle undercutting and sloughing of bluffs caused by beach--__------.------4 subsidence----__------..-.------.-- 4. Sketch of changes of beach configuration in sub- 11. Photograph of bluff erosion at Kenai ---_-_____-- mergentareas------______------.-.-- 5 12-14. Photographs of timber seawall on Homer Spit: 5. Photograph of deposition of material on backslope 12. As constructed --._------.------of frontal ridge------_-_____----__-___--_-8 13. Damaged, 6 months after construction._ - - 6. Aerial photograph of barrier beach at Breving 14. Almost completely destroyed by waves, 16 Lagoon, Seward Peninsula --__--____------9 months after construction-- .------7. Photograph showing undercutting and sloughing 15. Photograph of cobble-filled wire-mesh fence, of bluffs, Cook Inlet- ______--______-___9 Larsen Bay, Kodiak Island -.------_------8. Oblique photograph of new land created by tec- 16. Profiles of updrift and downdrift fill of grain at tonic uplift, Copper River Delta ------______11 Homer Spit---.------100 15C MILES
- - ---
1.- South-central Alaska showing cmstlines affected by the earthquake. Land to left of zero land-level change was generally lowered ; land to right was raised. THE ALASKA EARTHQUAKE, MARCH 27,1964: REGIONAL EFFECTS
EFFECTS OF THE ALASKA EARTHQUAKE OF MARCH 27, 1964, ON SHORE PROCESSES AND BEACH MORPHOLOGY
By Kirk W. Stanley
ABSTRACT
Some 10,000 miles of shoreline in were altered or destroyed on submerg- Streams were lengthened in the emer- south-central Alaska was affected by the ence but began to reappear and to gent areas, and down cutting and bank subsidence or uplift associated with the stabilize in their normal shapes within erosion hare increased. great Alaska earthquake of March 27, a few months after the earthquake. Except at Honler and a few small vil- 1964. The changes in shoreline processes Frontal beach ridges migrated shore- lages, where groins, bulkheads, and and beach morphology that were sud- ward and grew higher and wider than cobble-filled baskets were installed, denly initiated by the earthquake were they were before. Along narrow beaches there has been little attempt to protect similar to those ordinarily caused by backed by bluffs, the relatively higher the postearthquake shorelines. The few gradual changes in sea level operating sea level led to vigorous erosion of the structures that were built have been over hundreds of years, while other bluff toes. Stream mouths were drowned only partially successful because there more readily visible changes were sim- and some were altered by seismic sea was too little time to study the habits ilar to some of the effects of great but w'aves, but they adjusted within a few of the new shore features and to design short-lived storms. Phenomena became months to the new conditions. appropriate protection measures. Emer- available for observation within a few In the uplifted areas, generally around gence of large areas that were once hours which would otherwise not have Prince William Sound, virtually all been available for many years. beaches were stranded out of reach of below water and permanent submer- In the subsided areas-including the the sea. New beaches are gradually de- gence of onceuseful land areas have led shorelines of the Kenai Peninsula, veloping to fit new sea levels, but the to many problems of land use and Kodiak Islanjd, and Cook Inlet-beaches processes are slow, in part because the ownership in addition to the destruction tended to flatten in gradient and to re- material on the lower parts of the old or relocation of wildfowl, shellfish, and cede shoreward. Minor beach features beaches is predominantly fine grained. salmon habitats.
INTRODUCTION
One of the strongeat earthquakerj lowered as much as 71/2 feat and by the earthquake are included, ever reported occurred in alaska 25,000 'quare miles was raised as the shoreline within the area ex- on March 27, 1964, at 5:36 p.m. much as 33 feet (Plafker, 1965, ceeds 10,000 nautical miles. Alaska standard time. The epi- 1967). The coastlines affected by Certain changes in beach forms center was at Unakwik Inlet in the earthquake are shown by occurred as a result of relative Prince William Sound (fig. 1). figure 1. changes in sea level caused by up- The magnitude of the main shock Definite limits of the coastal area lift or subsidence of the land dur- was 8.4-8.6 on the Richter scale of Alaska affected by the earth- ing the earthquake. These changes (Wood, 1966). The area of land quake have not been determined. were abrupt and thus cannot be and sea bottom affected by the Most authorities, ho~vever,agree unconditionally compared to i~ earthquake is at least 70,000 square that it is bounded by Yakataga gradual change in sea level, but miles and may exceed 110,000. (just southeast of the area shown they did provide much informa- Forty thousand square miles was in figure 1) on the east and the tion regarding normal shore proc- Kodiak group of islands 011 the esses. Because sea-level changes southwest (Plafker, 1965). If all were not only abrupt but also ' Geologist, Anchorage, Alaska ; formerly Tidelands Supervisor, Alaska Department of the shoreline irregularities of the permanent, months were afforded Natural Rcsonrces. Division of Lands. mainland and the islands affected for observations, which other-
J1 52 ALASKA EUTRQUAKE, MARCH 27, 1964 wise-as during storms-would problems. These limited observa- available. Descriptions of coastal have been limited to hours or at tions do not reflect all conditions erosion primarily involve exam- the most several days. and processes that occurred within ples along Cook Inlet because (1) No attempt is made in this paper the area affected by the earth- much of the shoreline there is erod- to present a detailed description quake, but they do provide a basis ing and (2) the area is more of changes in beaches throughout for understanding the general densely populated than elsewhere. either the submergent or emergent processes that occurred. The earthquake not only caused areas. A study of this type might The chief objective of this report physical changes which have left have provided some interesting and descriptive material, but, con- is to compare pre- and post-earth- their marks upon the beach ; it also sidering the great distances and quake processes. For this reason, had certain significant economic the general remoteness of much of Homer Spit is used as an example and legal consequences. These so- the shoreline involved, such a for much of the descriptive mat- ciological effects have an intercon- study would have been impractical. ter; it happens to be one of the nection with the physical effects This paper is therefore restricted few places for which consider- and are considered worthy of to descriptions of specific areas and able preearthquake information is mention.
SHORELINES OF THE EARTHQUAKE-AFFECTED REGION
The line of zero land movement, formed in part of outwash de- posed of medium to coarse shingle. (fig. 1) trends southwest from the posits from the Bering and other Sandy beaches and constructional epicenter on Unakwik Inlet at the large glaciers. Westward from the costal forms occur along the head of Prince William Sound, Copper River Delta the shoreline heads of bays, however, and well- along the east shore of Kenai Pe- is glacially carved and is highly developed sand-shingle beaches ninsula, to Kodiak Island. West irregular, deeply incised, and tens of miles in length are present of this line the land subsided; to fringed by numerous offshore along the south~vesternmostpart the east it was uplifted. Anoma- rocks and reefs. The offshore area, of the island. lous areas of submergence, particu- particularly between the mouth of Along the southern Kenai Pe- larly along deltas and at the heads the Copper River and Cordova, is ninsula and the western part of of bays, occur in both regions and shallow and has numerous shoals, Prince William Sound, the shore- were caused by compaction and barrier islands, and spits. Active line resembles that of Kodiak Is- settlement of sediments. Compac- glaciers occupy the heads of many land in its irregularity, although tion of sediments in the uplifted bays in the region, particularly in bayhead depressions and subma- area reduced the overall upward Prince William Sound. rine rock ramparts at the bay change in some localities; compac- Along Kodiak Island the shore- mouths are less well developed. tion in the subsided areas accen- line is characterized by fiords in However, the presence of active tuated submergence. classic forms. The bays, particu- glaciers along the shoreline indi- The landmass bordering the larly along the Shelikof Strait side cates that many of the indenta- coastal area affected by the earth- of Kodiak Island, have deep de- tions are true fiords. Here also the quake is mountainous, and both it pressions at their heads and sub- walls of many of the bays are and the shoreline are characterized marine threshholds of either rock steep, and cliffs are more numerous by glacial or periglacial features. or unconsolidated material at than along Kodiak Island. Nar- The shoreline from Yakataga their mouths-a feature that, ac- row, relatively steep beaches con- northwestward to the Copper cording to Guilcher (1958, p. 160), sist predominantly of shingle. River Delta is characterized by denotes a true fiord. The walls of Sandy beaches occur along the long sweeping beaches broken by the bays are usually steep, and sides and heads of inlets and bays wide-mouthed rivers and resem- many headlands are characterized but are less well developed than bles a ria coast (Lobeck, 1939). by cliffs. Beaches are generally along the eastern shoreline of The shoreline features were poorly developed and are com- Prince William Sound. EFFECTS ON SHORE PROCE:SSES AND BEACH MORPHOLOGY 53
Contrasting sharply with the ir- ingly contradictory evidence of displacements and tho long-term regular shorelines of Kodiak Is- both uplift and subsidence-a con- trend of Holocene coastal emer- land and Prince William Sound is tradiction that perhaps is not sur- gence or sdbmergence, as well as a the more uniform one of Cook In- prising when viewed in the light remarkable widespread submer- let. Cook Inlet extends into the of the complex tectonic history of gence during the past several cen- mainland more than 175 miles and the region. The high Chugach turies over much of the zone that narrows and shallows towards its Mountains, Saint Elias Mountains, was uplifted during the earth- head. The backshore, particularly and Fairweather Range are ob- quake, and at least part of the zone east and north of the inlet, cun- vious manifestations of strong tec- that subsided (Plafker and Rubin, sists of low gently rolling glacial tonic uplift. Raised beaches along 1967; Plafker, 1968, in press). outwash plains. Wave-cut bluffs as some coasts indicate more recent Thus, according to Plafker, the high as several hundred feet occur uplift, also, but the drowned fiord- tectonic movements that acmmpa- in that area, and the adjacent like character of much of the shore- nied the earthquake were but one beaches are generally well devel- line, combined with numerous off- pulse in a long-continuing trend oped. At the head of Cook Inlet shore islands, skerries, and reefs, of diastrophic deformation that the waters are shallow, and broad suggest coastal subsidence and has resulted in regional emergence silty tidal flats are common. South of parts of the continental margin, of Tuxedni Bay, on the west shore submergence. of Cook Inlet, the low coastal plain Reconnaissance studies of the simultaneous submergence of the pinches out, and mountains rise displaced shorelines, paced by nu- Kenai-Kodiak Mountains belt, and abruptly from the sea. merous radiocarbon dates, hare either relative stability or emer- Much of the shoreline affected brought out a general similarity gence along the shores of Cook In- by the earthquake presents seem- between the pattern of earthquake let and parts of Shelikof Strait.
COASTAL FEATURES AND EARTHQUAKE EFFECTS
FEET loT Frontal ridge The beach face is the area be- or berm - - . H~ghwater tween high and low water (fig. 2). 30 FEET It is an ever-changing feature, but normally the changes are subtle and become noticeable only during m severe storms. /-eeUpperbeach face During the earthquake of 1964, i- Beach face rapid changes in land elevation caused obvious changes in shore 2.-Diagram illustrating beach features. processes and beach-faca morphol- ogy. These changes were wmpara- CHANGES IN PROFILE AND ent from 1:8 to 1:30 and are ble in magnitude to changes that GRADIENT characterized by a break-in-slope normally are caused by centuries- Obvious changes in profile and 50-200 feet seaward of the high- long fluctuations in sea level--or, gradient mumd along shingle water line. The break-in-slope marks the location where wlaves~act paradoxically, to sudden changes beaches within the submergent longest at high tide (King, 1959). caused by severe storms. Thus, areas. In those areas, changes were changes in the beach face follow- The beach face (fig. 2) shoreward noticed within 1 week after the ing the earthquake are important of the break (termed the "upper both to the study of fluctuating eartihquake. The most noticeable beach face") has a steeper gradi- sea level as it affects a beach and to change was a flattening of the ent and coarser material thsan dom the engineering problems that gradient and a recession of the the lower beach face. The break- might be met along the beach face beach face. in-slope shown in figure 3 is typical as a result of changes caused by Mfanyshingle beaches within the of those on many shingle beaches storms. submergent areae range in gradi- in Alaska. ALASKA EARTHQUAKE, MARCH 27, 1964 \
concluded in part that a raised sea level is follo~+-edby shoreward dis- placement of the beach profile as tlle upper beach is eroded and that the amount of lilaterial eroded fro111 tlie lipper 1)eacll is equal in vollime to that deposited on the neal.iliore bottoni. Thus the rise of tlie llearsliore bottom that results from this deposition will 111ti- nlately equal the original rise in relatii e sea level. Allong beaches protected froni .erere storm \\-ares, adjustnlelit to ~nbiidenccldiffered some\\ hat from that on exposed shingle beaches ,up11 as ITomer Spit. Within the l~rotectedareas, for example those :~lonrtlie iolltll side of Kxcheriiali 3.-Sharp break-in-slope bctn-een upper and lower beach faces extends from mid- Hay ant1 cncrtain shores of Kocliali foreground to miclccLnterof ~)hotogr;tl)h.just to right of man. These features, here seen Tb1:111(1. ~-e('essionof the beacsh facat. in Kacherrii~lrBay :rt lo\\- tide. ;krc, c.oul111on to niany shingle beaches. n-:ti ~liorcnliiforn~ i111d the convex- up~~-artlprofiles \\-ere less notice- After earthquake-caused sub- :~ctireerosion along the hreak-in- able l)cc.:rnae TT:L+ e action \\-as less sidence, n7:-aves reached higher on slopo and tlie de~elopmelitof a ~PJT- turljnlent. Erosion along the new tho beach face and caused severe 1)osteartllquxke frontal ridge. Ih- 1)renk-in-slope and s\vxsll action scour erosion of the upper face; ing tlris stage the beacli became along the bench (.rest \\-ert. also 1c.i the break-in-slope g r a d 11 a l 1 J not iceably convex ilp~vnrclbecause 5evcre. 'I'hus, the rate of beach-face shifted ihore~vard. T1~c 11pl)er ni:lterial from near the break-in- recwion along the heaches not lirnit of t,lie s~vasli\\-as also ex- ilol)~moved tol~arcl the upper ;ictr>don hy large naves \i-:ts more tended at sorne places, and the beach face. The third stage n7ah ruliforin and less rapid than :-along frontal ridge, or berni, n as orer- c.llar:~cterized1)) (lei elopmmt of a esl)oqcd 1)caches. flo~~ed.Part of the lnaterial erodcd ~vrll-definrld I~reak-ill-slope that F:+ en less noticeable changes oc- from the beach face \\--a, tlius car- liatl gradually -1liftecl 1:111cl\~-ard. c.llrrec1 long sandy I.)rac.lws, 11r.01)- ried by tlic s~vasl~oi-er the frontal T':~.osion :nld recession of the 1)eacll :11)1> I)rcau-;etheir gradient is nsu- ridge alld \\-as tleposited along tlie facar continued until tllc slope all- ally flatter than that of shingle landward side. lro:iJ~edthe ~~reenrtli~~unliegr~~- Ije:lc~llei and bectll~sc innd is less A good exan~pleof profile and d~ent.1)nring the tllircl stage tlie 1.entl11~-nloretl hy I\ arc. action t ha11 gradient cllangeh along :r illingle nclr frontal ridge increasecl no- 15 -1llligI~. beacl~within the zul~nlerpent:ireai tic.cal)l~ill heigllt and erentnally ( )ne ;I~CR of sl~lj:,idence \i-herr nas afforded by beache, lone retarded ovcrflo~\-. During this snlltly vlty I)c:lcl~rip~.rdomin:lte i- Homer Spit. ,Idjilstment of the st:r~e :tlso. sonle of the nlat~ri:ll 111'11er ('001i Inlet. That regioli ii ITonier Spit heaches to thr. nev c.:irried Ijy the longshore clrift lje- c~Il:~rnc~tt~~~~zel1)y an estu:lr*ine ell Iiigll-\t ater level IKIS gradual but gall to acc~uilulatealong tlie loner \ irolltlielit where tlir i)r:~cl~mate ran be descrihrd :IS occllrring in 1)e:tch fare near tllc l~reak-in-ilopr. r 3 1.1nl cao~i>iitslargclj of silt-sized three st,dg~s(fig. 4) . The fir-t -t nw I lie ok)srrred erosio~ialand depo>i- l):trtic*Ies clrrived froni glacicr-fed was characterize11 L)J irrcrc era- tional effects of :I relati1 ely raised sion :~nd planing ofl of the sea, level on tilie Homer Spit strenn~s(Knrlstrorn, l!)[i.t). Stor111 beach facar :-and crest by nave and k)excllos :-are in agreenlent \T it11 sug- T\-:IVCSieldom exc.eec1 4 feet in sl\~~asllover\\-ash. 1'al-t of the eroded gestiolls niade originally by Rruun height. Thc Iwnch gradient is as rr~aterial was carried itcross the (1962) and partly tested by low ai I :;io(l a~itl,bccn~lsa tho heacli beach crest and onto the ipit. The Sch\\-artz (1965) with small-scale is actetl 11po1i Ir)] a t id:tl range of second stage n-:ls cliarac*trrizedby 1:lboratory experiments. Brunn fcct, iilty nintl flats sevcnll EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY 55
MINOR BEACH FEATURES
1st stage Minor beach forms including cusps, small beach ridges, and steps
Postearthquake HWL ------began to reappear on all submer- gent beaches within a few weeks Preearthquake HWL Plan~ng-offof ------face and crest after the earthquake. The new beach cusps were generally poorly developed and irregularly spaced upon the beach. Some of the hol- lows were overly large-being 30- 40 feet wide as compared with pre- earthquake forms 5-15 feet wide. 2d stage The outlines of the forms were vague, and at some places one horn Face convex was two to three times longer than the other. In all known examples, however, when the beach face itself
Eroston along break In slope began to revert to the preearth- quake form, the cusps also began to develop gradually into pre- earthquake forms.
3d stage On beaches where the gradient was lowered by initial postearth- Postearthquake HWL quake processes, cusps did not re- EXPLANATION appear until the gradient had ------steepened, possibly because lack of Dashed llne represents preearthquake frontal rldge mobility of the materials retarded the formation of the beach cusps. Postearthquake break-ln-slope Solld line represents beach profile On beaches where the gradient was at varlous postearthquake stages initially steepened after the earth- Hlgh water llne quake, poor 1 y defined cusps formed early, that is, within 3 4.-Sketch of three stages that characterized the postearthquake changes of beach months after submergence. These configuration in the submergent areas. Sketch is based on behavior of the beach on cusps were alternately destroyed the Cook Inlet side of Homer Spit, but applies to many other beaches. and rebuilt by large storm waves, however-a process that suggests miles wide are exposed during low action of a storm is usually meas- that beach cusps will not form, or water. Subsidence of the region ured in hours. at least will not persist, if the was not uniform but was as much Within the emergent areas, as gradient of the beach flattens be- as 2 feet. Some beaches examined along the Copper River Delta, the low a critical gradient. Along shortly after the quake showed no profile and gradient of the up- Homer Spit, this gradient appar- noticeable change in profile or lifted beaches remain unaffected ently is about 1:20 for shingle gradient, but by mid-1967,3 years with respect to wave action. The beaches. after the earthquake, subtle changes that have taken place are Prior to the earthquake, small changes in profile had occurred. related to abandonment and beach ridges and steps occurred The action of shore processes stranding of the former beach along the upper beach face of most following subsidence of the coastal faces above high water, and to ex- shingle beaches. Submergence de- region and the resultant effects on posure to the normal processes of stroyed or greatly altered both the beaches were similar to the subaerial erosion. In time, of features. However, the ridges and effects of a severe storm. However course, new beaches mill develop steps began to develop in approxi- the changes resulting from subsi- below the abandoned ones to fit mately the same location on the dence must be measured in years, the postearthquake high-water postearthquake beach face about 3 whereas the maximum destructive lines. months after subsidence. Unlike J6 ALASKA EARTHQUAKE, MARCH 2 7, 19'64 beach cusps, the ridges and steps occurred in the runnels within a tion on the landward side, such as became stable within 1 year after few weeks after n he mrthquake, that by which a new frontal ridge submergence. and at numerous places exposed a forms along the crest of a beach. muah coarser bed material. During Instead, the process seems to be LOW-WATER FEATURES the same period the ridges became one of flattening and spreading of The most prominent lo\\--water rounded and more symmetrical in the material followed by a land- features on beaches are ridges, run- profile. The heights of many ridges ward movement of material en nels, and submarine sandbars. All increased a foot or more. At many masse. As the landward migration three forms \Yere modified by the places where the preearthquake of sand is slowed by its deposition earthquake, and the changes oh- ridges were hard enough to sup- at a higher elevation on the beach, served give some insight into the port the weight of a man without runnels begin to form. Water movement of material and the de- appreciable indentation, the post- draining from the beach contrib- ~~elopmentof such forms. subsidence ridges were soft. Ap- utes to the process by eroding sand proximately 30 days after the from the channels. The eroded RIDGE AND RUNNEL earthquake, many of the ridges sand is thereafter transported to had widened, some to as much as the 1011-er beach face where part Ridges and runnels occur along several hundred feet, from previ- of it is eventually carried do~vn- most beaches of low gradient ous widths of a few scores of feet. beach by littoral currents. For this where sand is available and where During the widening process the reason there was a persistent me- the tide range is large enough to adjacent runnels \\-ere partly filled, andering and relocation of the expose several hundred feet of and low basins were left in some runnel courses during the first beach face at low water. Good ex- areas to serve as drainage chan- year following subsidence, some- amples are found along many nels. Ridges and r~~nnelsthat were thing that had not been observed beaches of *4Easka but they are l~articularlyconspicuous prior to before the earthquake. The mean- especially conspicuous at Cook the earthquake were modified to dering process is a result of the Inlet. broad, somewhat undulating sand larger quantity of available sand The ridges are oomposed chiefly flats without definitely recogniz- and its increased movement along of sandy material ; the runnels, or able features. the low-water areas; part of the troughs, are floored with gravel. The landward shifting of tlie sand \\-as deposited by the ruimels The runnels provide cllaiinels ridges \\-as not a simple process themselves. \\-liich drain the beach on tlie ebb- of individual ridge migration. On new beaches within the up- ing ticle. King (1959) suggests Instead, the ridges were first lifted areas, particularly along that a correlation can be made be- rounded then widened, and finally the Copper River Delta, incipient trveen the most persistent ridges \\-ere coalesced-a process which ridges and runnels became notice- and the position at which the tide often obscured and obliterated the able about a year after the earth- will stand for the longest period iilterveniilg runnels. No appreci- quake. They were poorly devel- during the tidal cycle. The ridges able seaward migration of mate- oped, perhaps because the newly along the Alaska coast are usually rial occurred. The predominant formed lower foreshore had not fairly stable, particula~rly those landward migration seems to bear yet stabilized with respect to gra- that are alined parallel to the coast out King's statements (1959) that dient and profile. In part, material and perpendicular to the direction sea\$-ard of the plunge zone, or in the ridges was transported land- of the dominant wave approach. break-in-slope of the beach face, ward and deposited on the upper I11 profile the normal sand ridge there is a definite landward migra- beach face or on frontal ridges is asymmetrical, not unlike a rip- tion of material. along the new high-water line. A ple mark, but on a much larger One year after the earthquake, few preearthquake sand ridges sca'le; seawlard-facing slopes are most of the ridges and runnels had and runnels were partly stranded steeper than shore\\-ard-facing stabilized in approximately the above the high-water line and so ones. In general, iildividual ridges same configurations as those be- were altered or destroyed by near the low-water line are higher fore the earthquake. storm I\-aves. than those farther up the beach The landward migration of the face. ridges apparently is not a simple SUBMARINE SAND BARS I11 the areas of land subsidence, process of removal from the sea- Limited observations iiidicate a noticeable scouring of sand ward side of the ridges and deposi- some relocation of submarille bars. EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY 57
This relocation is suggested by ridges along t'he Alaska coast are RESPONSE TO SUBSIDENCE AND UPLIFT previously reported hard bottoms composed of shingle, often with in anchorages that, after the earth- minor amounts of sand. A beach Changes in beach ridges occurred quake, were composed of soft sand. ridge along the present s~horelineis in many submergent areas. The This condition was particularly generally referred to as a modern magnitude of the changes depend- noticeable along Homer Spit or frontal ridge, whereas the ed 'on (1) the extent to which the where scuba diving showed that ridges farther inshore are referred land was submerged, (2) the geo- preearthquake areas of hard- to as ancient or old ridges. graphic location of the beach with packed sand were characterized by Most individual ridges are 5-6 respect to storm wavw, (3) the soft loose sand within a year after feet above high water and 8-10 slope of the bmch face, and (4) the the earthquake. feet wide, but some are as high as type of hach material. In shel- In some areas, particularly in 20 feet and their bases may be as tered areas where submergence was Prince William Sound, submarine \vide as 200 feet. Most ridges even- only about 1-2 feet, changes were sand bars apparently were altered tually become stabilized by rege- minor, but in areas of grealter sub- or destroyed by seismic sea waves tation that establishes itself on the sidence and exposed sea conditions or by local waves. G D. Hanna Iand\vard slope. the changes \\-ere often major. (written commun., 1966) states Frontal ridges grow gradually In \some areas, su& as along that soft sediments were scoured in both height and width by the Homer Spit, subsidence mused from many shallow bottom areas. deposition of mterial carried onto waves to reach as much as 6 feet Elsewhere submarine bars were al- and across the ridge crest by waves higher on the beach face than be- tered even though tsunami effects and swashes during storms. ,4s the fore the earthquake, and swashes were not evident along the shore- ridges increase in height, the abil- overflowed the crest of the frontal line. ity of the ovenVashto carry debris ridge. Material along the upper across them decreases. Thereafter beach face, which was formerly MODERN BEACH RIDGES material will accumulate along the above all but the highest waves Beach ridges (also referred to as sea\~arclside of the ridge; as the and swashes, was mured and e~od- "beach storm berms") occur along accumu1:it ion of debris progresses, ed. Pa& of the evoded material was many of the beaches of Alaska; in a second ridge, seaward of the carried by the swash across the the submergent areas many of earlier one, will begin to form. crest of the frontd ridge and de- these ridges were altered during The entire process nlay then be posited along the landward slope the earthquake. Observations since repeated. (fig. 5). the ea17thquake have provided in- The time span between develop- ASoverflow of tallefrolntal ridges formation on the formation of ment of successive riclpes is rari- continued, material eroded from beach ridges as \\-ell as their adjust - able, I~ingabout a year or less the beach face, including the face merit to relatively higher sea level. :ilong certain narron- stable of the frontal ridge, was carried Reach ridges of south-central beaches (a "stable" beach being de- onto the lracksllore and deposited *4laska are more perfectly formed fined as one not enlarging sea~vard there. Continued overflow and along shingle beaches than along or retreating land\vard) but se~-- erosion of the preearthquake fron- era1 hundred years or more along sand beaches where most are small- tal ridges reduced the crest height such large fornls as cuspate fore- er and less well developed. Most and caused the eroded material to lands and spits. constructional coastal forms, such spread out along the backshore. as cuspate forelands, spits, and It is generally accepted that The beaches along Homer Spit tombolos, are formed and enlarged coastal forms, such as cuspak by the development of successive forelands and spits, widen sea- (Stanley, in Waller, 1966a) are beach ridges along the shoreline. ward by the development of suc- good examples of postearthquake The usual beach ridge consists cessive par:tllel and subparallel beach-ridge development. Within of a mound or \vindro\vlike deposit beach ridges. The landward parts approximately 30 days after the along the beacli immediately above of such coastal forms are usually earthquake, the beach face i11 some the high-water line. King (1959, p. characterized by a series of old areas had receded as much as 15 353) considers the ridges to he the vegetation-covered beach ridges feet, but the frontal ridges had ill- product of steep stonn waves that represent forrner shorelii~es creased as nlucl~as 30 feet in width which thron- debris above the that trend parallel or subparallel and 2-3 feet in height. As the fro11- reach of normal waves. The larger to the present shoreline. tal ridges widened, coarse debris
EFFECTS ON SIIOItE PItOC6SSES AND BEACH MORPHOLOGY J 9
6.-Pxrt of the harricr hcnch :rt R~PT~IICI.;reoct~i. Sr~\\-:~rtlPt~rii~~si~l;~. T.irzoor1 is rlortll of (:ll)o\-c,I 11c:1(.11: n~ri~lgSew is wolltll of (helo\\) Ijanch. Tlre lagoon~vartl~llii.r:~tio~r of tlrt~I~;rrric,~. Irc~;~c.li i. -11on.111)$ ~111)1t~r1)ositiol1of tilt' ov~"rflo\\~11p011 tllt* c'11~11:lt~~ spit . Alosr hcnc.11~~~ill l IIP earlE~cln;ikc>-;lffcc.tc.tll!a IT 11f -\1:1nli:1 illi er;~rt,~ll;l~rd~\;lrd ollly short tli\t:i II(.~%SI~c~c~:rlrne they \rere hnclrrcl I)g land l~latfo~rr~~st11:lt :~llo\\t~tLo\.rr\\-;r>lr 111;1t(,ri;l1to ;I(~(.IIIII~I~;ITI,.I'~I~I~IIc~:I~!~I /I$ .\l;~sl ~.--SII~!III~~~~I~II(~I~(.:111net1tI1t1 l~igll-\\-:~tt>r li111~ to q11ift to :I Irigll(,r elevation 0x1 this I,t~:lt.ll011 tllr. c~:~stc~rrrsllorc. of ('ooli 1r1lc.t. T11t. t~~t:rI~lislr~nt~ntof n riel\- high-watcar I 1.o1111rei1tti11 I lol~gl~ingof I~lrift's Sot(%;~bsrnco of l)ri~c'hritlgtls. J10 ALASKA EARTHQUAKE, MARCH 27, 19 64 along the preearthquake lower by seismic shaking may also con- height from compaction and set- beach face does not form stable tribute 60 a change of coastal tlement, therefore, probably would beach ridges as readily as does forms. The 1964 earthquake caused occur between the modern frontal shingle. The old ridges in the up- compaction and settlement of sedi- ridge and the mainland and wvuld lifted areas will gradually be ments in many parts of south-cen- lead to the typical basinlike profile covered by vegetation and will tral Alaska (Kachadoorian, 1965 ; that characterizes so many coastal then assume the character of the Coulter and Migliaccio, 1966 ; Wal- constructional forms along the typical old beach ridges of many ler, 1966a). Coastal forms must south-central coast of Alaska. coastal areas. New ridges along the have been subjected to similar com- lower high-water line will begin to paction processes many times : STREAM-MOUTH CHANGES develop as material continues to During the past 50 years that offi- Stream mouths were changed be worked by waves. However, the cial records have been kept, hun- throughout the areas of uplift and new ridges probably will require dreds of earthquakes have occurred subsidence. In uplifted areas, several years to {stabilize, mainly along the Alaska coast (U.S. Coast streams were lengthened and in- because of a lack of coarse source and Geodetic Survey, 1964, p. 23). cised into the elevated beach face. material. As new beach ridges develop, In the submergent areas, streams the coastal form widens seaward mere shortened and dro\vned. ANCIENT BEACH RIDGES with a corresponding increase in Postearthquake studies of sub- thickness of the column of sedi- SUBMERGENT AREAS sided coastal forms afford an ex- ment. The coarsest material is usu- ally near the mainland and the Stream mouths were drowned planation for the fact that the throughout the submergent areas. crests of some ancient ;beach ridges smaller particles along the seaward side. If the mass of this sediment Maximum drowning occurred are uniformly lower than the mod- mostly at the mouths of low.-gra- ern or frontal ridge. In some areas is repeatedly subjected to seismic and niicroseismic shocks, the sedi- dient streams that flowed across this condition is sufficiently pro- low-flying backshores composed of nounced to result in a basin-shaped ments-particularly the finer par- ticles-will lose bearing capacity n-ater-laid sediments. Within such area between the frontal ridge and areas, subsidence is attributed both the mainland. This habit of Alaska and settlement will follow (Ter- zaghi and Peck, 1948). In some to tectonic movement and compac- beach ridges has also been noted tion of the sediments (Kachadoori- elsewhere (Bird, 1964; ,Johnson, kinds of sediments, vibration can lead to sl>ontaneous liquefaction an and Plafker, 1967, p. F27 ; Ka- 1919). chadoorian, 1965, p. B2), and the Johnson (1919), Fisher (1955), which would cause additional set- tlement. extent of stream drowning is a and Zenkovitch (1959) attribute function of both. the relatively lower crest elevation Even though the coastal form nearest the mainland is oldest and The most notable examples of of the older ridges to a continuous hence has been subjected longest stream-mouth drowning are along rise in sea level whereby each suc- to seismic action, the sediment lay- the shores of Kodiak Island and cessire frontal ridge builds higher. er there is thinnest and the size of the southern Kenai Peninsula This is well illustrated along the particles is coarsest. Compac- where subsidence of the land \\-as Homer Spit; as a result of the tion by seismic shaking, therefore, 5 feet or more in some locations earthquake-caused rise in relative \I-ould be less in such areas than (Alaska Dept. Fish and Game, sea level, the frontal ridge here has i11 the seaward part of the land- 1965). Several excellent photo- been built higher than the older form where the sediment is thicker graphs of drowned streams on ridges. If a rise in sea level is the and the particle size is smaller. Kodiak Island are shown in a re- only factor at work, however, the Although the modern frontal port on that area by Plafker and profile between the frontal ridge ridge has been subjected to fewer Kachadoorian (1966). and mainland should have a gentle earthquakes than have the ancient During the earthquake ~nany landward slope rather than the ridges, sediment compaction does hays along Kodiak Island were commonly observed basin-shaped occur there also. However, any de- hit by seismic sea wares. Spits, profile. crease in height caused by compac- bay-mouth bars, and barrier Studies by the author after the tion would perhaps be offset by the beaches at or near stream mouths earthquake suggest that compac- addition of new material brought were altered or destroyed. Some of tion and settlement of sediments in by waves. Maximum decrease in the lower of these landforms were EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY Jll nvern :tslled, eroded, :1iid redurctl in hcigl~t. ?Je\x~ outlets fori~~ccl 11-here tllr tsunamis tore cllanllels tlirt-n~gliriilgei and spits. In all c>xar~~y)lesIciio\rn to the writer, strenlll rllouths tl~at \vcro actetl 111)oil l)y tslulaniis were ~videlicd I)y scolu. ailcl erosion. Sii~cetllc e:~rtllil~r:~l\cl.crosioil 1)) nornlal wa\-c :tild a-li orerflnn has grndnnlly i~:~l~~cdIII:LILJ.e20:15t:1l features s11(*11ai '111t- ;liltI barricl 1)c:~chcs t,) flatten 111 l)l,nfile :tilt1 r-ecedc lallil\.-artl. 'I'!III-. tlic cficc~ of the ~\ILII:IIII~:11i(1 of 1ioi.111:11J\ t3 :t(*tioil1i:ls ~~d~l(*e(li1l:t11~oii(*c (aoi~ spici~o~~hfor111\ to f1:lt ttl~l(~l,1)oorl~ ticfilled tlclt:~lil\cl fc:lt~irci.111 io111~> :rrcas of :I(ti\ e il~ori. drifting. mnteri:rl cl.otl(~l1)) \\a\-(\ act io11 5.-Tectonic 1111lift c.rcsatt~dXI(,\\- lands pt~rnlarlc~ntlyabove high v-ater, such as this fro111 tll~.t~,e:ti~~ 111or1tli. h:ti re- ;rrc,;1 :1101ig tlit~Copper River r)t,lta. Vir\\- :it liigli tide, st~vt~rnlmonths after the earth- ~)lc~~lil~otlt11v 1)cacli :~loirg tlic 1111;11;(,. Thv 1)rrt~artliclu:ilic~liigli-\r:~tt'r lir~cx is shown a1)groximately by the dashed line. ilo\vnd1*ift -lilt. 111 al.e:ls of 11 e:ll, 1'11otogrirl)ll 11y17.S. Fort~t S('rvice. or innctirt, \lio~~drifting the eroilttl 111:~tei,1:11i- 111c>rel)5prc:ttl out on tli~lo\\ ri. I~c:~c-llt':tc.c. I)?- tllix tlcc-rc~:~~cd>111)ply of mnte- from the niouths and carried 15-ith 111 (*crt?ri11\tre:t~i~\ of lo\\ gr:t(11- rial is 11ot \ c,t calt,:li.: I~o\\.rver,be- other debris into the upper re:xches tlilt ailil 1 (llo(>it?,t 11t \11!1rt>i\v(,i~~ ~:LIIXof :I cl(v~l~(~:lsc~ill +t~,o:~~~~-l~o~-iic~ of tllc streams. Snc.l~ dcl)osition snl)jcctetl 1 o itrong \\ :I\-~I:tc,tioi~ ~naterial, I~rc*:1r~>t~\\-itlcr st ren,lll c>nuscd c~onsitlcr;tbl~silting ill \\hell t11e 1:111il 511!)~i(I~~(l,:111(1 lll:lt(~ i~lontlls n-ill I 1 loilgsliorc strean1 monthi and channels, and ~.i:~lcrotlcil fro111 tl~tl ~~i~c~o~l~oli tlriftiilg :r11t1l~y-;~:ts>i~ig of i~~:ttc~- in some streant5 rauaecl :I trmpo- (l:ltt>(liI(,]li~::it? :tlollg' tllt>il, I)>tllIis, ri:11, :t11i1 I1rc-:11l-e ol' (.ontinning rary d:rnin~ingor blocking. Spits snc.11 :ts i1elt:rs :t11t1 o11t \\ :is11 f:llls. \v:~\-t.:tc,tio~~, I)c,:rcall (~1,osioil1)roI)- :t~lcl 1)urrier ridges at stre:xni \V:IS tr:~iisl)o~,to(l1)) \1:1\-i+i111o t11(, I ill c.I~:ll.;l!~ti~rizt.r11ai1y oloatlls \17ert generally :~ltrredby stre:~ni111outlis. This process is 1~1'- ~lro\Vli~~ll.tl~c~~~l~l-lllolltll :Irtl:ts for tlic tsull:tlriis. illally of tlit Io\\-cr ti~-~~l:\rly~ioti(x~:il~lo :~IIIII,C 'IY~~l~~1- lll:tll)- y(,:ll > to 1~~11,1c~, I)e:tcli forills \\-ere :tl)precial)ly :tg:tiil .I~~IIiii ~~l)l)(>i, ('I 101~ IilIc,t. c-liangetl. :tll(i 1ri:~terial was redii- \\-l1cr.c~IIIIIII i~ :~('I,IIII~II!:I~~II~ill UPLIFTED AREAS tribl~teclalong !.lie beach illto the tlro\\-11ctlst i,i'allr ~IIOII~~I-. 1 stre:lni i11o11tll. Slwh ~vdistrilnltio~~ I11 some :wens tlie (ll.o\vliil~gof lii r 11r 111out11i of ti :tl.t> of the n~:tterial eve11 ol)l~ier.ated strtr:tnls 112s ilrc*rc:!-otl tl~i>1111)111). itr~:~illiill tl~(x11111iit(~I SOIIIC ~tre:lniI~OII~SES. of 11r:lt c,r.ial for 11:~t111,:tl II~~:L(.~Irelated to sitca111-I(III~..(~ le~lgtl~rii ~lo~~~risli~~~i~t~t.I<)- l~tvl~i~.i~~gstrt:~~~ il~p :r~itl (lo\\lic311ttllle ( fie. h). 1o1 1ci1nl~lifted , . ilioreli~~csc~olil1)owtl of s:11it1 :111d g:liit. S~I~II~IIIi:rs l(>dt o I licie c.h:~llgci1.~111g(' f I 0111 11111101. hilt, 1.:111i(l g~~ll~i~ig(I(Y,II~~(Y~ :~t 1)1,o;:i~:t(lit1,2i~:~tl~(~i, t 11:ti1 (lt>gi~:~(lii~g 'tlterat~oir- :IIOII~iI~or(~l~i~rs of it~.e:rni11to11thi (fig. 0) . Alloiigtlic of l~l1:lllllc~l>.st t~(L:ltll~~~~ll~~lllll tiler(>- littlc nl~liI't to 111:~jolc~11ailec~- :tlolig ('ol111er Ri\ cr 1)clta. ill.cn of fo~,t.i- lrss rtt't.c,ti~rt!l:111 it \\-:I. g!.cutl~ -lolung. rnc,il~ c>~otled ro:tdily erodecl 5:t11tl :111d \l!t t11:tt I)c:~calicbIn nre:ti I 1i:tt 11 cl t. :~l)11ir>- \\:ti n1)liftetl several frrt, gllll~iilg c.1:t111y 111'1lFt~il. ro~i~l~~cllc*eel11 itliili 1ioili.h :tttoi. 111)- Tllc cKec.~s of tslui~:~~liison lift (12ci111ilitz :tilt1 11:rr-li:tl I, stl-can~ mol~tlls in tile upliftctl 1965). R:tl)icl Iie:td\~:trtl c.rosio~~ areas arietl n itlclg. 111 manj ~)l.o(luc.etlsrl1:tll I\ :ttel.f::ll~1-"eet places. sand ancl silt \x7ere scoured 1~1gl1. 512 ALASKA EARTHQUAKE, MARCH 2 7, 1964 wave erosion, none were aflected nlore than the east shore of Cook Inlet from Kilchemak I3ay to Turnagain Arn-a distance of Inore than 170 lniles (fig. 1).There the entire sllorelinc ii eroding. -1s already mentionecl, the shoreline is a relatively mlil'ornl smicly hcach \\.it11 slopei ni lon as 1: 300. The tidal range ii :111out 22 feet along the southern iection hut increases to more t1i:tii :iO feet near Tnm- again *inn. I3ecause of the lo\\- bcaell or:~clirnt :tnd high tidal I*xngr, qe~-c.ral thousaild fret of tldelailils itre exposecl :it low 11-ater. The 1)ench is backed by a line of bluffs nl~out200 feet high in most place<. 1)11tlocally as high as 600 9.-Rapid gullying and sloughing c.:~u.etl by I~enclunrd \trranl rro.ion xlong the feet in tll" Homer of uplifted coast on the Copprr Rirer Delta. Photograph by U.S. Forwt Srrricr. the I)lnfPs are of unsorted el:~i.ial ~llnterialthat is easily eroded. Prior to tl~c~ar.tliqllakr, 11-ave Along beaches of mixed sand 01-era11 result \\-as an 111ci-eaie 111 :~ction n as n~ltlrrc*nttliig the I~lnffs :xnd shingle, stream it~ljust~i~eilti 11iateri:ll ttarrietl 1)) the -trealili in ni:ln> areas. Most of tllr ixncly were slower. Small rifflci formetl ant1 tl(~~x>\lte(lat tllelr mouth-. f~-:xcztionof tlie ilonghetl mntrri:~l at stream mouths along sni~li ilo11g iolile .tre:tm nrollthc, tile tlriftctl nnay, hnt part of tllr beaches. nenlv drpoiited iiintcr~alllai re- cno:ti.ier nla teriul rer~~:~in~tl:llong Kirkby and Kirkby (1368) de- t:lrtletl t.han11c1 del elolj~~~clltittld tl~rlli~Ii-\\-atcr line ill tllr form of scribed in detail stream-n~ontllnd- ha- led to nieanrlering. A\lo~lgthe -l~iiigl(>on 1)e:tch ri(1gw. 'I'lie justment along e1ev:tted intei-tidal Ii~rgeritrcnn~s the 111 ocae\ili:t\ l)ecli l.i(lre., n l~ich\\-ere :ts Iiigll :IS 3 zones composetl of i:~ntland i111n- 111:ti111yiilting <111(lcll--ectioll of fect. ~)i.otc~c~tedthe topi of the Ijlllff- yle at Montague Island. IT here ul) - newly forliled tlelt:t+ ant1 -l)~t-. t'1.0111 :t11 the l:~rgc>l.\torn1 lift \\-as as mnch as 3:: feet. .ti on A1ltliough r\ it1cnc.e inil118nte. ,111 \\ Tllc t\r o r-on~~il~initics:~lollg tllii shoreli~~eriiost ~('riollslg:~tTected by k111tA erosion were Kcnni :nld Hoii~c~.I SHORE PICOTECTION MEASlTRES II:x(*ept at F'Ioirier and a fe\\ in~:~llrillages, 110 serious efTort has /)eel1 nlxtle to cw1lstrnc.t crosion- preveiltive \~-orltsnny\~-llere ill tlre c~:trtliqunke-nffectc(I area. .iloiig tlie Cook li~letside of Hoilier Spit, rroiio~ioil tli~lee iide of the groln far1 hcit (lo\\ ndrift 1)ec~unlecarit iral. I?etl.e;rt of tllr I)eacll n:li jeolx~rd- iziiq tlic> -1)it Ii~glln:~~.111 ,Ji~ly I!)(\ L. ,I -c,ln ail :uitl tn o :~tltlitiolial 11. Scrions l)li~Rerosion c.:~nvtl117 snl)sitlt~~lct~nlong tlit~n-ntelrfrnnt of tl~rxto\~-li of ci.oi11-.\\ cBl.ccno~ritl-l~cte(l. TI\ o 1ilu1- Keliui. Tie\\- lool;il~g~~orth\\-+~>t\\-nrtl. ;11,o11t 30 ~I:IJ-.;~ftcr tlic~ f~:~rtl~cln:~kt.. tlrcYl feet of tl1c \\ :111 \\:ti cAoll- ~trl~,*tt~lto :I Iie~gllt of 1-2 feet :lI)ovr t11(1111gli \I :lt(>rli~ir, :1i1cl one 13) lD(ii. :3 ycari :ittc.~t 11~ r:rlfli 111cdi:lt(>sin' sto1~111n :t\ C\ it ill ircatioil n:ti I~l~ilt5 feet liiplier (p:~Ice,t11~ 1)lntl 1111~111 -ollicX:LIY?:I< ( l!I(i'7) cr.otlr tlic to(>\of tlic b111ffi. :ti)o\t> t11e l~igli-\v:tte~.line. F'ign1.e l1:1(1 rere(l(~c1ii~fli(*~eiitl~ to ~)IY)\ 1(1(> I -11til tlic I)ll~tfl ilie 1.tc2ctlcicilol~gli 19 slio\\ s tlio tiiiik)e~b1ilklie:rtl nntl :I. I\ ~(ltliof l)~> 12.-Timber seawall and new groIns along west side of Homer Spit as constructed 334 months after earthquake-caused subsidence. 13.-Sea~vnll shown in figure 12, approximately 6 months after construction. EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY 515 ancl~oretliu u~lhtablebctlcli gravel. Else\vlicre wire-mesh baskets filled with rabbles were placer1 long the beacli to serve as bulk- Iieatls. Snch baskets appeared to fillletion we11 :dong I-Iomer Spit, (.yen though they were pounded E)y \va\ es :rs high as 10 feet. Erosion, nioveover, occwrred 011 ileitlier the updrift nor the do~vndriftside. ,I siniilar c.oW)le-fillecl wire-mesl~ fenre was started at liarsen Hay 011 Koiliak Island (fig. 15), hut r~iostof it IT as destroyed by storni waves before it co11ld be com- pleted. IITave erosion of landslides callsed 1)y the earthquake was rapid, particularly :rlong Cook In- 14.-Sean~all shown in figwe 12 some 16 months after c'onstruction. Note that the let ~11ewtlie frontal eclges of the kjullrhmd and orir of thr groins 11 err c.oml)lettblydrstroyctl tluririg thi\ period owing to slides \vc.rr greatly n~odifietl~vitliin th~irrsc.rscirc hcight 2 ycars. 34any slides caonsisted of sandy-silty inatei*i:~l. Silty-mud 1)eaches linve deve1ol)etl gradnally, particularly on the clo\~-iidrift sides. Erosiol~ within the uplifted areas is evitlent along the post- e:trtllqllnke lo~~erliigll-water line. Wave erosion along most of the npliftetl nrea is not serious so far :IS loss of 1:rnd is c-oncerned: )nost streanls xc-ross elevated tid;ll fl:rts :Ire inrising ch:nl~iels. LONGSHORE MATERIAL MOVEMENT No significant changes resi~lting from thc earthquake arc kno~vi1or reported for the directional habit of the longshore drift. The changes that 1l:rrt. occurred are only in the q~~a~~tityof material carried. 1.7.-Cobble-filled wire-11le.11 fence under caoristruction at Larsrr~Ray, KodinB 1cl:ultl. A1lollg111oit sliorelines ntFected Ir~y hhortly after tlie enrtlicl~ialit~trricl res~iltantsnbsidcric.c~ of 2 frrt. .\Itwt of tlir frllc.t, tlie c:rrtlic~nnke,more m:rterial Iia3 Ira.; drutrcyred by a utorrli I~rforrit co111d116, c>tnriplrted. entered tl~clongsl~ore tlrift than Iwfore. months later, respectively. Sixteen collstructed in other areas but The nddition:rl m:rterinl hepn months after construction, the rrlost were destroyed within several to c~ltcrtlie sen in~l~ietliatelyafter high timber bulkhead between the months, or at most within a year, tlie earthquake. This fact was fifth :ind iistll groin had been de- after the earthquake. Failure is 1r1:lde ok)rioils along nl:\ny shore- stroyed. as had the last groin (fig. attributed to the fact that the lilies by n hro:td 1)and of niuddy 14). Similar high bulkheads were bulkl~eadswere too high and were 1%-aterthat w:ls several miles ~vitle ALASKA EARTHQUAKE, MARCH 2 7, 1964 I'-\ -.-._ I--. ..-----__--<--- .-- I;... EXPLANATION '<--- FEET 12 Groin l01 ---- Downdrift, southeast side ------Updrift, northwest side 0 30 FEET I I I I 1 I I I I I I 33 52 67 80 96 125 150 166 184 196 216 MEASUREMENT POINTS 16.-Profiles of updrift and downdrift fill of groin ait Homer Spit, measured (A) an March 2, 1964, a few weeks prior to the earthqtmke; (B) on August 23, 1964, 4 months after submergence; and (G) on September 30, 1965, 18 months after submer- gence. The change in configuration of the groin fill was caused by submergence and the resultant higher level of water on the fill. Note, however, 'that the gradient at 18 months approximates the preearthquake gradient. EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY 517 in some areas, but no direct effect, quake (Stanley, in Waller, 1966a). ends of the groins (fig. 16B),but such as the formatiion of new Significant changes in material about 30 days after the earthquake berms by the deposition of the ma- movement may therefore have the iiitergroiil fills began to en- terial, was observed along beaches passed unnoticed. large, and thereafter the enlarge- until several weeks after the eartli- Tlie study was made by the ment increased noticeably. The quake. A good example of the effect Alaska Division of Lands along inaterial causing the increase prob- of a delayed longshore drift is de- the west side of Homer Spit at a ably was brought there by the scribed by Stanley (in Waller, system of filled groins that had longshore drift. 1966a, p. D24). At Homer Spit been studied prior to the earth- Observations indicate that dur- the additilonal quantity of material quake. After submergence the ing the 30-day period following that had entered the longshore high-water line rose 3.3 feet. With- the earthquake, the material de- drift in the source area, 2-6 miles in 5 days after submergence, 1-2 posited along the beach crest came west of the spit, did not reach the feet of material had accumulated from the lower-upper beach face spit until about 30 days after the along the laiid~vard end of the of the groin fills and was carried earthquake. groins ancl hacl spreacl inland to :i upslope. Erosion along the lower- Aocelerated shoreline erosion in width of 30-50 feet. The iie~vl~de- upper beach face continued until a the submerge~lltareas caused more posited irlaterinl was first thought new profie of equilibrium had been material to enter tlie drift than to have been carried ill by the long- established. The dominant move- had been entering before the earth- shore drift. Howel-er, the first pro- ment of material during the 30- quake. Hou-ever, in the same areas, files made 7 days after submer- day period following subsidence material contributed by rivers and gence indicated that the iiltergroin was upslope because the waves streams decreased. The converse fills had actually receded and were reaching higher up the beach was true in the uplifted arm. flattened and all had undergoile a face. Waves running higher up What effect the change in balance net loss of material (fig. 16A). In- the beach face shorten the travel of the source and supply of mate- asmuch as )the material lost from distalice of the s~vashand thus in- rial will have on the character of the intergroin fill area about crease its carrying capacity. the l~ongshore drift is not yet equaled tlie iie~vlydeposited ma- Tlie increasecl shoreline erosion known. In pl'anning future coastal terial along the 1aiid~v:~rdend of throuyliout the area unquestion- the groins, the material probably projects the possible changes in ably increasecl the supply of ma- was derived froin the adjacent in- source and supply that have m- terfill area rather than from some terial to the lonpsliore drift ; after curred since the earthquake must c1ist:uit source. about :3O days a noticeably in- be taken into consideration. Additional profiles were made creased quantity of material mas drifting alongshore, but during UPSLOPE MATERIAL MOVEMENT at about 15-day intervals for the next 60 days (fig. 16B, C). Within this first 30-day period follo\ving Only one limited study of ma- the first 30 days the intergroin fllls submergence the dominant motion terial movement mas made ~x~itl~in receded as inaterial continued to of material \\-as up the beach the first year follo\viilg the earth- accumulate along the landward rather than 'along it. BIOLOGIC EFFECTS OF SHORELINE CHANGES damage to this resource has not yet Kodiak Island, important inter- FISH been made, the environment and tidal spawning grounds mere habitat of tlie sallilon is kno~~*nto iiituidated. At the time this report mas hare beell drastically changed in G. Y. Harry, Jr. (written conl- written (1967), the most compre- some :\reas. i~itui., 1964), reported, 5 months hensive discussion of tlie effects of Part of Prince William Sound after tlie earthquake, that the the earthquake on tlie Alaska fish- was npliftecl as much as 33 feet, greatest damage to the salmon in eries was tlie one compiled by the and great changes in the environ- Alaska was probably in Prince Alaska Department of Fish and inent and habitat of pink and William Sound; here 75 percent Game (1965). Although a com- chum salmon resulted. Similarly, of the pink and chum salmon pro- plete analysis and assessment of in tlie submergent areas, such as duction comes from tlie intertidal 518 ALASKA EARTHQUAKE, MARCH 2 7, 1 9 6 4 spawning areas. Thorsteinson the preearthquake lower areas are WILDFOWL now characterized by excasive (1964) states that within Prince Ordinarily submergence or quantities of sediments that de- William Sound the runs of pink emerpnce m-ould not be considered salmon range from 3.2 to mil- orease the survival rate of salmon 8.7 to affect waterfowl adversely, but, eggs and alevins. lion fish and the chum salmon according to P. E. K. Shepherd from 0.4 to 0.6 million fish. SHELLFISH (written commun., 1966), there Compounding the permanent has been an indirect effect. In the damage caused by uplift and sub- One of the more important feeding ground of the dusky Can- mergence of the intertidal spawn- habitats of shellfish, particularly ada goose in the Copper River ing grounds was the temporary the razor clam, is along the Copper Delta, the preferred food of the effect of tsunamis and local waves. River Delta. The delta was up- goose is a type of vegetation refer- In parts of Prinae William Sound, lifted as much as 8 feet, and, be- red to as "forb-grass." This the waves caused considerable cause of the low offshore gradient, grass--actually a combination of scour, and debris and silt were car- extensive intertidal areas were herbs and grassesappareiltly re- ried upstream for several hundred permanently elevated above high quires occasional inundation by feet. Some biologists believe that water. This area supported a large marine 3%-atersand usually grows many salmoll eggs were scattered population of razor clams. The along the sides of tidal sloughs and by the movement of debris. When, widespread death of these and other areas regularly inundated by all contributing factors in Prince other bivalves throughout Prince the highest tides. Because of William Sound are taken into ac- TVilliam Sound was evident changed tide levels, the fo~b-grass count, the salmon loss caused by within a few weeks after the earth- is dying, and before it is reestab- the earthquake and its subsidiary quake (G. B. Haven, written lished at a higher elevation, the effects is thought to be about one- commun., 1965). Many of the clam dusky Canada goose is likely to quarter of a million salmon (Noerenberg and Ossiander, beds are now above high water and have changed its habitat. Shep- 1964). are lost, but clam beds formerly herd indicates that the habitat of In the Kodiak Island area, below lower low water were the goose may be further changed where submergence was as much elevated and are now accessible to because its former nesting grounds as 6 feet, widespread flooding of clam diggers. In some areas of \\?ill become overgro\~-nwit11 coni- the intertidal spawning areas oc- Prince William Sound, particu- fers or other plants 11-hen the salt curred. In some places flooding of larly dong the western part, su'b- is leached out of the soil. To some the intertidal area was helpful to sidence at the baylieads was caused extent these same changes are af- the salmon in that \vaterfalls by local compaction of the sedi- fecting the habitats of the dab- which formerly obstructed their ments. Consequently, clam be'ds bling and diving ducks and the upstream migration were elimi- 15-hich were once readily accessible trumpeter swans. nated. Along other streams, sub- are now from 2 to 4 feet below low Brakish-water lagoons and mergence and flooding increased water and out of reach to conven- sloughs are favored as the size of the intertidal area. Re- tional methods of harvesting. nesting or feeding grounds by moval of waterfalls in some areas some \~ildfo~~-l.Uplift drained and enlargement of other areas, There is no general consensus as thus increased the size and avail- to whak long-term ecological effect some of these areas or made them ability of certain intertidal either submergence or emergence less brackish because of the inflow salmon-spawning grounds. has had upon the general clam or of fresh water. Thus, changed en- W. L. Sheridan (written bivalve population wit hill the af - rironnients, whether caused by up- commun., 1965) stated that the fected areas. Certainly the initial lift or submergence, may ulti- changes in the inhrtidal spawn- mortality rate was higll-es- mately contribute to a decrease in ing habitart and environment have pecially in the uplifted areas-as the wildfowl population in specific not been fully assessed, but that was proved by tlie skeleton. In tlie areas. Whether new ~~ildfo~~lconi- future production will decrease. submergelit areas the greater inunities will spring up in areas Although some intertidal spaiwn- depth of water now present over inade more favorable by the earth- ing areas have increased in size, the outermost clam beds has also quake 11-ill not be knoll-11 for some Sheridan indicates that many of resulted in bivalve mortality. years. EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY J19 EFFECTS ON PROPERTY VALUES AND MANMADE STRUCTURES Earthquake-caused uplift and after the earthquake when tides of emergence, it has also been subsidence-and the consequent mere high. Several cannery necessary to relwate the installa- changes in coastal processes-af - wharves and loading platforms tions upon which barges, mws, feated the legalities of land owner- had to be raised. In some places, and fishing boats are stored in off- ship, and also led to many changes such as at the Wakefield Cannery season months. At tlle beginning in property values and necessita- at Port Wakelfield on Kodiak Is- of the 1964 fishing season, follow- ted reconstruction or ~=elocationof land, complete relocatioll of the ing the earthquake, some craft had illany CO:LS~:L~installations. A fenv cannery was necessary. to be pulled from their storage of tlle resultant problems are I11 some s~~binerge~ltareas, wave areas onto the tidal flats by tractors toudled on here. scour has moved large quantities before they could be refloated. of gravel under or away from can- SUBMERGENT AREAS neries ancl other facilities built LEGAL PROBLEMS As already mentioned, coastal over the high-water line. For ex- Because the State of Lilaskahas erosion is occurring in many of the ample, a cannery at Larsen Bay on jurisdictioil over the bottoms of submergent areas, and in some Kodiak Island, which was built in all navigable waters, legal prob- areas-such as on the Kenai Pe- a seemingly ideal location and was lems have arisen wherever land ninsula-the rate of bluff recession adequately protected before the raised or lowered by the earth- is several feet per year. In other earthquake has incurred consider- quake abuts navigable waters. In areas, erosion may still become a able storm damage since the earth- Alaska the boundary of tidal problem although the process is quake. Erosion of gravel from the waters is the line of mean high not yet noticeable. One such area adjoining beach has endangered tide. is along upper Cook Inlet where some of the cannery buildings. A person whose Alaskan prop- submergence \\-as less than 2 feet. EMERGENT AREAS erty abuts the line of mean high The dramatic effects seen in areas tide is called an "upland owner." of greater submergeilce are not Some of the immediate effects By common-la\\- principles the up- present in this area, but there is of emergence that necessitated land om-ner enjoys t~ll littoral unquestioi1ably a gradual retreat economic and engineering consid- rights and privileges afforded him of the shoreline. This retreat is oc- eration were related to small-boat by the lmtion of his land. Such harbors. In the Cordova area the curring in some of the more rights and privileges include, densely populated areas where land was elevated about 8 feet. There emergence necessitated among others, free and unob- land values are high. dredging and enlarging the small- structed ingress and egress to the At Turnagain Arm, wave ero- boat harbor. Some of the channels sea. sion has damaged road and rail- of the Copper River Delta that The line of mean high tide thus road embankments that were had formerly been accessible to is the legal boundary that sep- raised after the earthquake. Wave fishing boats required considerable arates the upland owner's private erosion in that area will probably redredging in order to afford ac- property from Dhe State-owned continue, and the embankment will ce~ssafter the earthquake. I11 some tidelands. The line of mean high require constant surveillance ancl uplifted areas, individuals who tide remains fixed unless the shore- maintenance. In Homer, wave formerly had access to the sea by line is altered by accretion or ero- action has already damaged sec- shal1011- channels or tidal sloughs sion. If these processes result from tions of the nelr-Iy constructed found it necessary to dredge their natural causes and the shoreline Homer Spit highway. access routes. In otlher areas, land- changes are gradual and imper- Some shore i~lstallations that ing facilities, such as docks and ceptible, the legal boundary will escaped severe damage at the time wharves, could no longer accom- change location to match the line of the earthquake were, because of modate deep-draft vessels and had of mean high tide. However, if the the higher stt~ndof the sea, endan- to be enlarged or relocated. changes are natural but sudden in gered by flooding a few weeks In Cordova, because of the 8 feet character and wholly perceptible, 520 ALASKA EARTHQUAKE, MARCH 2 7, 1964 the process ijs tenmed "avulsion," (State of Allaska Attorney Gen. who enjoyed all the righiis and and the legal boundary remains Opinion 6, Sept. 14, 1964). privileges afforded them as upland fixed even trhough the mean high Along the uplifted coasts many owners befiore the eaMhquake now tide line has been displaced. private parcels of Iland abutted the find themselves undble to exercise Movement of the land during the line of mean high tide before the their littoral rights and privileges. earthquake was abrupt, certainly earthquake ; afterwards, however, The opposite has occurred in the occurring within a matter of hours the natural line of mean high tide submergent areas. There, owners if not of minutes, and flooding or was shifted seaward, in some places of land that abutted the line of ~vithdrawal )of waters from the several hundred feet. Because mean high tide prior to the earth- land was equally abrupt. On Sep- temlber 14, 1964, he attorney gen- wibhdrawal of the water has been quake now find their boundary line eral for the State of Alaska de- defined as avulsi~on,the private (tlhat is, the preearthquake line of scribed this process as one of ownership cannot follow the re- mean high tide) some distance sea- avulsion and therefore the legal treating line of mean high tide but ward of the natural mean high tide boundary line--the line of mean must instead remain fixed to the line. These persons in fact own high tide-remains fixed as it was line existing the insbant before the tidelands but the lands are legally the instant before the earthquake earthquake. Thus those persons described as uplands. NEmED FOR FURTHER STUDIES One danger in attempting to probably did nlot all'm for full such areas, the result more often rectify ooutal-erosion problems is consideration of design mebhods than not promotes rather than re- that protective measures are often with respect to unnatural slopes; tards wave erosion. taken without a clear understand- such slopes can promote wave ero- The installation and construc- ing of littoral conditions. 'Phis sion. Time did not always allow tion of shore protective works will problem has already manifested for adequate investigation of near- undoubtedly become necessary itiself at various lolcalitieis where shore conditions, such as wave long before a profile of equilibrium inshallations that were constructed runup and current direction; con- de\-elops and stabilizes-a profile to protect the land have in fact sequently, adequate safeguards to which will itself eventually retard destroyed it. insure maximum protection shoreline erosion. Therefore, the Some of the later damage to against coastal erosion were not economic ramifications of coastal mads and embankments may per- designed. Certainly, in the submer- erosion not now readily noticeable hlaips be explained by trhe rather gent areas the sea has encroached may, within the next few years, be- hurried reconstruction efiort im- upon the land establishing a new come a problem which must be mediately following trhe earth- profile of equilibrium. When arti- dealt with if valuable areas of land quake. The necessity for haste ficial impediments are placed in are to be saved. REFERENCES CITED Alaska Department of Fish and Game, Bruun, Per, 1962, Sea-level riw as a Fisher, R. L., 1955, Cuspate spits of St. 1965, Post-earthquake fisheries cause of shore erosion : Am. Soc. Lawrence Island, Alaska : Jour. evaluation; an interim report on Civil Eng. Proc., v. 88, paper 3065, Geology, v. 63, no. 2, p. 133-142. the March 1964 earthquake effects Jour. Waterways and Harbors Div., Guilcher, Andre, 1958, Coastal and sub- on Alaska's fishery resources : no. WW 1, p. 117-130. marine morphology [translation by Juneau, Alaska, 72 p. Coulter, H. W., and Migliaccio, R. R., R. Iv. Sparks and R. H. W. Bird, E. C. F., 1964, Coastal landforms ; an introduction to coastal geomor- 1966, Effects of the earthquake of Kiieese] : New York, John Wiley phology with Australian examples : March 27, 1964, at Valdez, Alaska : and Sons, Inc., 274 p. Canberra, Australian Natl. Univ., U.S. Geol. Survey Prof. Paper 542- .Johnson, D. W., 1919, Shore processes 193 p. C, p. C1-C36. and shoreline deveolpment : New EFFECTS ON SHORE PROCESSES AND BEACH MORPHOLOGY 521 York, John Wiley and Sons, Inc., Plafker, George, 1967, Surface faults on Termghi, Karl, and Peck, R. B., 1948, 684 p. 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Geoscience, the L-Ionier area, Alaska, with a see- raised by the 1!364 earthquake, Mon- Osaka City Univ., r. 10, art. 1-7, tion on Beach changes on Homer tague Island, Alaska: U.S. Geol. p. 53-66. Spit, by K. W. Stanley: U.S. Geol. Survey Prof. Paper 54SH. (In Surrey Prof. Paper 542-D, p. Dl- Reimnitz, Erk., and Jlarshall, X. F., press. ) D28. Lobeck, A. K., 1939, Geomorphology ; 1965, Effects of the Alaska earth- l966b, Effects of the March 1964 an introduction to the study of quake and tsunami on recent deltaic Alaska earthquake on the hydrol- landscapes : New York, McGraw- sediments : Jour. Geophys. Re- ogy of south-central Alaska : U.S. Hill Book Co., 731 p. search, v. 70, no. 10, p. 2363-2376. Geol. Surrey Prof. Paper 544-A, p. Noeren~berg,W. H., and Ossiander, F. J., Schwartz, Maurice, 1965, Laboratory A1-A28. 1964, Effects of the ;\larch 27, 1964, study of sea-level rise as a cause \Yood, F. .J., ed., 196667, The Prince earthquake on pink salmon alevin of shore erosion: Jour. 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