Re ional Effects

Copper River Basin Area

GEOLOGICAL SURVEY PROFESSIONAL PAPER 543-E

THE ALASKA EARTHQUAKE, MARCH 27, 1964: REGIONAL EFFECTS Effects of the Earthquake Of March 27, 1964 In the Copper River Basin Area, Alaska

By OSCAR J. FERRIANS, JR.

A description and analysis of the earthquake­ induced ground breakage, landsliding, regional uplift and subsidence, and damage to manmade structures in the Copper River Basin

GEOLOGICAL SURVEY PROFESSIONAL PAPER 543-E UNITED STATES DEPARTMENT OF THE INTERIOR

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY

William T. Pecora, Director

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1966

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 THE ALASKA EARTHQUAKE SERIES

The U.S. Geological Survey is publishing there­ sults of its investigations of th.e Alaska earthquake of March 27, 1964, in a series of six professional papers. Professional Paper 543 describes the re­ gional effects of the earthquake. In chapters of this volume already published, studies of slide-induced waves and seiching at Kenai Lake, geomorphic ef­ fects in the Martin-Bering Rivers area, gravity sur­ veys of the Prince William Sound region, and effects of the earthquake on Kodiak and nearby islands have been reported. Other professional papers in the series describe field investigations and reconstrqction and the effects of the earthquake on communities, on the hydrologic regimen, and on transportation, utilities, and communications.

CONTENTS

Page Page Page Abstract _____ ------______E1 Geologic effects of the earth- Geologic effects-Continued Introduction and acknowledg- quake______E8 Ground cracks and associated ments______2 Regional uplift and sub- landsliding-Continued Geographic setting______2 sidence______8 N elchina River delta__ _ E17 Origin ______Physiography______2 Changes in ground- and 23 Climate______3 surface-water conditions__ 8 Lateral extension __ 23 Roads and settlements_____ 3 Ground water______8 Horizontal com- Geologic setting______3 Surface water______8 paction ______23 Bedrock______3 Cracking of lake and river ice__ 10 Differential verti­ Major tectonic elements____ 3 Ground cracks and associ- cal compaction __ 24 Unconsolidated deposits____ 6 a ted landsliding______11 Snowslides, rockslides, and 24 Permafrost and seasonal Terminology______11 avalanches ___ ------frost______6 Effects of the earthquake on General distribution___ 11 manmade structures ______25 The earthquake and its after- Geologic controls______11 Damage to buildings and shocks______6 Little Tonsina River site__ 13 associated structures____ _ 25 Seismic data______6 Other landslide sites____ 13 Damage to highways and Ground motion ____ ------7 N elchina River outwash bridges ______------25 Sound______7 apron______17 References______- _- __ 27

ILLUSTRATIONS

FIGURES

Page Page Page 1. Index map showing the loca­ floor of Little Tonsina 17. Aerial view of north end of tion of the Copper River River valley______E14 the large Nelchina River Basin area ______E2 10. Large ground crack parallel­ delta along the western 2. Generalized geologic map of ing north side of small hill shore of Tazlina Lake____ E21 the Copper River Basin near mile 65, Richardson 18. Aerial view of Kiana Creek area ______Highway______15 4 delta along eastern shore of 3. Map showing major tectonic 11. Photograph of pressure ridge Tazlina Lake______21 elements of flouth-central on flat surface bordering Alaska ______19. Aerial view showing large in­ 5 Little Tonsina River_____ 15 4. Map showing recent regional 12. Large ground crack formed undated area along eastern uplift and subsidence in in clearing along south shore of Tazlina Lake____ 22 south-central Alaska ____ _ 9 shore of lake______16 20. Diagrammatic sections show­ 5. Aerial view of the northern 13. Aerial view of the large ing mechanism of forma­ end of Tonsina Lake ___ _ 10 braided flood plain of the tion of basic types of 6. Aerial view showing intensely Nelchina River______17 ground cracks______23 fractured· ice along the 14. Photograph ortypical ground 21. View of pavement surface of crack in outwash apron of eastern shore of Tazlina the Richardson Highway_- 26 Nelchina River______18 Lake ______22. Little Tonsina River bridge 11 15. Vertical aerial view of Nel- 7. Map showing the distribution china River delta______19 shoved from right to left of ground cracks ______by landslide movement___ 26 12 16. Vertical aerial view of ground 8. Sketch map of the Little cracks along and parallel­ 23. Small crack across aban- Tonsina River landslide site__ 14 ing hingeline on Nelchina doned section of road on a 9. View of pressure ridges on River delta______20 low gravel terrace______27 v

THE ALASKA EARTHQUAKE, MARCH 27, 1964: REGIONAL EFFECTS

EFFECTS OF THE EARTHQUAKE OF MARCH 27, 1964, IN THE COPPER RIVER BASIN AREA, ALASKA

By Oscar J. Ferrians, Jr.

ABSTRACT

The Copper River Basin area is in Copper River was completely dammed March, seasonal frost was present south-central Alaska and covers 17,800 and Tazlina Lake drained proved erro­ throughout the area. square miles. It includes most of the neous. Despite the diversity of local condi­ Copper River Basin and parts of the The ice on most lakes was cracked, tions, the origin of most of the ground surrounding Alaska Range and the Tal­ especially around the margins of the cracks can be explained by the following keetna, Chugach, and Wrangell Moun­ lakes where :floating ice broke free from mechanisiil.s : ( 1) lateral extension, tains. the ice frozen to the shore. Ice on Taz­ caused by materials moving toward an On March 27, 1964, shortly after 5 : 36 lina, Klutina, an~ Tonsina Lakes was unconfined face such as a lakeshore, p.m. Alaska standard time, a great intensely fractured by waves generated river bluff, hillside, or terrace escarp­ earthquake having a Richter magnitude by sublacustrine landslides off the ment; (2) horizontal compaction, of about 8.5 struck south-central Alaska. fronts of deltas. These waves stranded caused by repeated alternate compres­ Computations by the U.S. Coast and large blocks of ice above water level sion and dilation (in the horizontal Geodetic Survey place the epicenter of along the shores. River ice was gen­ direction) of materials in flat-lying the main shock at lat 61.1 o N. and long erally cracked in the southern half of areas where there are no unconfined 147.7° W., and the hypocenter, or actual the area and was locally cracked in the faces ; ( 3) differential vertical eompac­ point of origin, from 20 to 50 kilometers northern half. tion, caused by the shaking of materials below the surface. The epicenter is In the area of study, the majority of that vary laterally in thickness or near the western shore of Unakwik In­ the ground cracks occurred within a ra­ character; and ( 4) combinations of the let in northern Prince William Sound ; dius of 100 miles from the epicenter of above. it is 30 miles from the closest point the earthquake. Ground cracks formed Snowslides, avalanches, and rock­ within the area of study and 180 miles in flood plains of rivers, in deltas, and slides were restricted to the moun­ from the farthest point. along the toes of alluvial fans. They tainous areas surrounding the Copper Releveling data obtained in 1964 after also occurred locally in low terraces River Basin. They were especially the earthquake indicates that broad adjacent to flood plains, in highway numerous in the Chugach Mountains areas of south-central Alaska were and other fill material, along the mar­ which are closest to the epicenter of the warped by uplift and subsidence. The gins of lakes, along the faces of steep earthquake. The large amount of snow configuration of these areas generally slopes of river bluffs and hillsides., and and rock debris that has cascaded onto parallels the trend of the major tectonic in areas cleared of vegetation for sev­ the icefield and glaciers of these moun­ elements of the region. Presumably a eral years. tains, and, probably even more impor­ large part of this change took place dur­ The ground cracks were restricted to tant, the overall disturbance to the ice ing and immediately after the 1964 earthquake. areas underlain by unconsolidated de­ field will affect the regimen of the The water level in several wells in the posits where one or more of the follow­ glaciers. area lowered appreciably, and the wa­ ing conditions existed : ( 1) permafrost Most of the damage to manmade ter in many became turbid; generally, was absent or deep lying, ( 2) the structures occurred in the southern however, within a few days after the ground-water table was near the sur­ half of the area, and, primarily because earthquake the water level returned to face, ( 3) bedr6ck was relatively deep of the sparsity of population and man­ normal and the suspended sediment set­ lying, and ( 4) slopes were steep. Be­ made structures, property damage was tled out. Newspaper reports that the cause the earthquake occurred in not great and no lives were lost. E1 E2 ALASKA EARTHQUAKE, MARCH 27, 1964

INTRODUCTION AND ACKNOWLEDGMENTS

The Copper River Basin area, as ate properly the engineering Since most ·of the people live defined in this report, covers about significance of the earthquake. near the highway, a systematic 17,800 square miles in south-central Because of the U.S. Geological study along the roads provided Alaska (fig. 1) ; it includes most of Survey's geologic mapping of the fairly comprehensive coverage of the Copper River Basin and parts Copper River Basin, in progress damage to manmade structures. of the surrounding mountains. since 1952, the general distribution In the vast, inaccessible areas away and character of unconsolidated from the highways, the distribu­ deposits in the area are well tion of earthquake-related features known. Without this work, ade­ was determined by observation quate evaluations of the effects of from light fixed-wing aircraft. At the earthquake would not have several sites where landings were boon possible during the short time possible, these features were ex­ available for field investigation. amined on the ground. Observations of the effects of the I am greatly indebted to all of earthquake in the Copper River the individuals who provided eye­ Basin were made between July 2 witness accounts of their experi­ 0 200 400 MILES and July 23, 1964. During the ences during and immediately I I I I I 3:1;4-month interval between the after the earthquake. Rich Hous­ 1.-Location of Copper River occurrence of the earthquake and ton and Cleo McMahan, both bush Basin area. the time when observations were pilots, not only did an excellent made, undoubtedly many earth­ job of chauffeuring, but also con­ Its boundary on the east is long quake-related features, especially tributed their own time and energy 144°00' W.; on the north, lat 63°- subtle ones, were obliterated. Be­ to making critical observations 00' N.; on the west, long 147°40' cause of this time lag a large part pertinent to this study. James W.; and on the south, approxi­ of the discussion about earthquake B. Small of the U.S. Coast and mately coincides with the axis of Geodetic Survey provided relevel­ da~age to manmade structures is the Chugach Mountains. based . on eyewitness accounts; ing data, Robert M. Chapman of The primary purpose of this in­ the U.S. Geological Survey made however, most of the discussion vestigation was to determine the available an unpublished report concerning the natural earth­ effects of the great Alaska earth­ which included his observations quake of 1964 fn the Copper River quake-related features, as distin­ along the Richardson Highway Basin area and the geologic factors guished from damage to life and made soon after the earthquake, that tend to control the distribu­ property, is based on the author's and several individuals of the tion and character of these effects. observations and on the study of Alaska Department of Highways An understanding of these geo­ postearthquake aerial photo­ provided data concerning damage logic factors is necessary to evalu- graphs. to the highways.

GEOGRAPHIC SETriNG

PHYSIOGRAPHY the east by the Wrangell Moun­ the bordering mountains are ex­ The Copper River Basin is bor­ tains. tremely rugged and they support dered on the north by the Alaska The basin floor is aplain of low numerous glaciers, which, along Range, on the west by the Talk­ relief into which the major streams with their melt-water streams, eetna ·Mountains, on the south by have cut steep-walled valleys as have cut deep valleys opening into the Chugach Mountains, and on 1nuch as 400 feet deep. However, the basin. EFFECTS IN TRE COPPER RIVER BASIN AREA E3

The greater part of the area of Louise, Crosswind Lake, and Ewan miles long, extends from Anchor- study is drained by the Copper Lake. Tazlina, Klutina, Tonsina, age to Tok Junction on the Alaska River, which originates from large and Paxson Lakes are large water Highway ; t,he Richardson High- glaciers on the northern side of the bodies occupying deep valleys in way, 365 miles long, extends from Wrangell Mountains. From its the mountainous areas surround- the ice-free port of Valdez to Fair- source the river flows in a large arc ing the basin. banks. Locations along these around the northern, western, and highways are designated by the southwestern sides of the Wrangell CLIMATE number of miles from the point of Mountains, and then southward origin of the highway-along the through the Chugach Mountains The Copper River Basin area Glenn Highway, miles from An- into the Gulf of Alaska, Major has an arctic continental weather chorage, and along the Richards011 tributaries to the Copper River in- regime with short warm summers Highway, miles from Valdez. clude the Chistochina, Sanford, and long cold minters. Mean an- Other roads within the area of Gakona, Gulkana, Tazlina, Klu- nual temperature, as recorded at study include the Edgerton High- tina, Tonsina, and Chitina Rivers. the Gulkana Federal Aviation way and the Lake Louise Road. The northwestern corner of the Agency Station in the east-central The Edgerton Highway, a two- area is drained by the Susitna part of the area of study, is 27"F., lane gravel road in the southeast- River which originates from a and mean annual precipitation is ern corner of the area, is 39 miles large glacier in the Alaska Range. 12 inches. These climatic condi- long and corlnecb Chitina with the From its source this river drains tions are signific:tnt to this study Richardson Highway. The Lake southward to the Copper River because they are conducive to the Louise Road, also a two-lane Basin, then makes a sharp turn formation and preservation of gravel road, leads north from mile and flows westward through moun- permafrost (perennially frozen 160, Glenn Highway, for approx- tainous terrain to the north end of ground) -and the presence or imately 19 miles to Lake Louise. the Susitna Lowland; from here it absence of permafrost is significant The settlements within the area flows southward to Cook Inlet. in relation to the distribution and are concentrated along or near the Within the area of study the ma- cha~acterof earthquake effects. major highways. Glennallen, the jor tributaries to the Susitna River principal settlement, of the area, are the Maclaren and Oshetna ROADS AND SETTLEMENTS with a population of around 200 Rivers. people, is near the junction of the A small part of the southwestern Large segments of two major Glenn and Richardson Highways. corner of the area is drained by *4laska highways cross the Copper Other settlements include Chitina, the Matanuska River which flows River h as in area. Both highways Copper Center, 3ulkana, Gakona, westward to Knik Arm of Knik are paved two-lane roads which Chistochina, and Paxson. Several Inlet. connect coastal cities in south- roadhouses and some service enter- The basin floor is dotted with central Alaska with interior prises are located along the high- lakes; the three largest are Lake Alaska. The Glenn Highway, 314 way between these settlements.

GEOLOGIC SEWING

BEDROCK wide variety of igneous rocks. MAJOR TECTONIC Mountainous areas around the Extensive areas are underlain also ELEMENTS margin of the Copper River Basin by a considerable thickness of un- There are six major tectonic ele- and prominent hills within the altered basaltic and andesitic ments within the area of study basin are underlain by altered lava. These rocks range in age (fig. 3, p. 6). From north to volcanics and interbedded gray- from middle Paleozoic to Pleisto- south, they consist of the Alaska wacke and slate, and by virtually cene. The distribution of bed- Range geosyncline, the Talkeenta unaltered sediments, all of which rock within the area of study is geanticline, the Matanuska geo- have been intruded locally by a shown on figure 2 (next page). syncline, the Seldovia geanticline, 2314.93 w6.62 E4 ALASKA EARTHQUAKE, MARCH 27, 1964

Base from Anchorage, Wo rld (N . Am erica) 1:1000000 sca le, compiled by Army Map Service

EXPLANATION

~ ~ Coarse-grained unconsolidated deposits Fine- and coarse-grained unconsolidated Bedrock ranging in age from middle of Recent age deposits of Pleistocene age Paleozoic- to Pleistocene 0 10 20 30 40 MI LES

2.-Generalized geologic map of the Copper River Basin area. Geology compiled by Ferrians, Nichols, Williams, and Yehle; Grantz (pl. 23 in Andreason and others, 1964); and Coulter and Coulter (1962) . EFFECTS IN THE COPPER RIVER BASIN AREA E5

150" 148° 146. 144°

0 50 JOO MILES /

i 4~~" Base from U.S. Geo logica l Survey 1:2 500 000

3.-Major tectonic elements of south-central Alask!a (after Payne and Dutro, in Miller and others, 1958, pl. 2). Geosynclinal area (troughs) shown by light stippling; geanticlinal areas (arches), by heavy stippling; and the Copper River Basin, by diagonal lines. E6 ALASKA EARTHQUAKE, MARCH 27, 1964 and the Chugach Mountains geo­ east-central part of the basin, these cleared of vegetation for .several syncline (Payne and Dutro, in deposits are quite thick. The ex­ years, such as those along the high­ Miller, and others, 1959, pl. 2). act thickness ~s unknown; how­ way net or in settled areas, the In the central part of the area the ever, as much as 400 feet is well permafrost table (top of perma­ Cenozoic Copper River Basin is exposed in bluffs along the deeply frost) occurs from 10 to 20 feet be­ superimposed on several of the entrenched rivers, and near Glenn­ low the surface. In contrast to other tectonic elements. allen a water well 502 feet deep the fine-grained deposits, the bottomed in unconsolidated de­ coarse-grained gravel deposits UNCONSOLIDATED posits. In the western part and along the major streams generally DEPOSITS along the margin of the basin, are free of permafrost. Perma­ these deposits generally overlie frost generally is also absent near In the mountainous areas sur­ bedrock at relatively shallow large deep lakes because of the rounding the Copper River Basin depths. The distribution of un­ enormous amount of heat held in the floors of the major valleys are consolidated deposits within the these large bodies of water. In the underlain predominantly by un­ area of study is shown on figure 2. Chugach Mountains south of the consolidated sediments of Pleisto­ basin, permafrost occurs as iso­ cene and Recent age. These sedi­ PERMAFROST AND lated masses where local condi­ ments are chiefly outwash gravel SEASONAL FROST tions are favorable for its forma­ deposited by glacier-fed streams tion and preservation (Ferrians, and till deposited by glaciers Permafrost and seasonal frost 1965). which formerly covered the valley were important factors in deter­ floors. Locally, significant thick­ mining the distribution and char­ Seasonal frost generally pene­ nesses of colluvial deposits are acter of ground cracks and land­ trates to depths from 2 to 4 feet in present. slides. Most fine-grained uncon­ poorly drained environments such The greater part of the basin it­ solidated deposits in the Copper as marshes; however, in well­ self is underlain by lacustrine, gla­ River Basin are perennially frozen drained environments such as cial, and fluvial sediments of from 1 to 5 feet below the surface gravel terraces, seasonal frost gen­ Pleistocene and Recent age (Karl­ to depths of as much as 200 feet. erally penetrates from 10 to 20 strom and others, 1964). In the In similar areas that have been feet.

THE EARTHQUAKE AND ITS AFTERSHOCKS

SEISMIC DATA at lat 61.5° N. and long 147.7° W. During the first month after the and the hypocenter at a depth main shock more than 7,500 after­ Computations by the U.S. Coast between 20 and 50 kilometers. shocks were recor

GEOLOGIC EFFECTS OF THE EARTHQUAKE

REGIONAL UPLIFT AND p. 4). Because of the lack of con­ became turbid. Generally within SUBSIDENCE trol points, the location of the iso­ a few days after the earthquake, base lines are only approximate. the water level returned to normal During the summer of 1964 the In spite of the sparsity of control and the suspended sediment set­ U.S. Coast and Geodetic Survey points, it is obvious that a broad tled out. Three wells in the Glen­ completed aproximately 900 miles area, including a large segment of nallen area were reported to have of first-order leveling in Alaska the Chugach Mountains, part of gone dry after the earthquake. areas affected by the earthquake. the Talkeetna Mountains, most of Water from a spring on the About 680 miles of this was re­ the Copper River Basin, and the north side of the Glenn Highway leveling of previously established Cook Inlet Lowland, did subside, near mile 140 was reported to have first-order leveling. Releveling and that large areas to the south been turbid and salty to the taste was accomplished between Seward and north of the subsided area after the earthquake, but within a and Anchorage via The Alaska were uplifted. The subsided area few days the condition of the wa­ Railroad, between Anchorage and fo~ms an arcuate trough sloping ter returned to normal. Glennallen via the Glenn Hi

4t 146' Base from U.S. Geo logica l Su rvey 1:2 500 000

4.-Areas of recent regional uplift (hachured) and subsidence (stippled). Isobase lines are solid where control is good and dashed where control is poor. Northernmost 0-isobase line ~epresents approximate limit of detectable change in altitude. El0 ALASKA E;ARTHQUAI(E, MARCH 27, 1964

&-View, to the northeast, of the northern end of Tonsina Lalre showing intensely fractured ice and 1arge.blocks of ice stranded above water level along the shore. The lake is about half a mile wide at this point. Photograph by U.S. Army, April 8,1964.

drained. Examinations by per- the Tiekel River, and ice jams near this general pattern. Ice on Klu- sonnel of the U.S. Geological Sur- miles 74 and 78.5, Richardson tina Lake and Tonsina Lake was vey and the A.laska Department of Highway, dammed the Tonsina highly fractured throughout (fig. Highways, several days after the ~iver: In both places, explosives 5). On Tazlina Lake the ice on earthquake, produced no evidence were used to blast channels the northern half of the lake was that the Copper River was, or had through the obstructions to pre- highly fractured (fig. 6), but ice been, completely dammed. Water vent the river from flooding the on the southern half was fradured was flowing in the main channels highway. of the Copper River and the water only around the margin, and a few in Tazlina Lake was near its nor- CRACKING OF LAKE AND linear cracks were formed across mal level for that time of the year. RIVER ICE the lake. The geabr intensity of Large waves were generated on The earthquake caused the ice the cracking of ice on these lakes Tazlina, Klutina, and Tonsina on most lakes to crack, especially was caused by water waves gener- Lakes by sublacustrine landslides around the margins of the lakes ated by sublacustrine landsliding off the fronts of deltas. These where the floating ice broke free off the fronts of large deltas built waves stranded large blocks of ice from the ice frozen to the shore. out into the lakes. above water level along the shores In addition to the breakage along River ice c r a c k e d locally (fig. 5), and at the outlet of Taz- the shores of the lakes, a few linear throughout the area of investiga- lina Lake, sediment and large cracks commonly formed at a tm- blocks of ice were carried over the gent to the shorelines. In many tion. At several places along the rapids and a short distance down places these linear cracks extended Nelchina, Sanford, and Copper the Tazlina River. completely across the lakes. Rivers the cracks formed a sys- A large snowslide near mile 50, Tazlina, Klutina, and Tonsina tematic reticulate pattern, easily Richardson Highway, dammed Lakes were major exceptions to recognized on aerial photographs. EFFECTS IN THE COPPER RIVER BASIN AREA

6.-View, to the east, showing intensely fractured ice along the eastern shore of Tazlina Lake, across from the large Nelchina River delta. Large blocks of ice stranded above water level along the shore are easily discernible, but the intense fracturing of ice away from the shore is obscured by the refreezing of the lake water and by a postearthquake snowfall. The segment of shoreline shown in this photograph is about half a mile long. Photomaph by U.S. Army, April 8, 1964.

GROUND CRACKS AND AS- For this reason and becauw of linear zones (fig. 7), and thus sug- SOCIATED LANDSLIDING other inherent difficulties with this gests that they were not caused by

I classification, I have used the gen- fault movement in bedrock beneath TERMINOLOGY eral term "ground crack" which the unconsolidated d e p o s i t s . The terminology for ground has no specific generic connotation. Rather, the distribution pattern cracks caused by earthquakes has indicates that local geologic factors GENERAL DISTRIBUTION I been inconsistently used in the controlled the distribution of the cracks. Nevertheless, the possi- I literature. The terms "fissure," In the area of study, the ma- \ "fracture," "furrow," and "ground jority of the ground cracks oc- bility that fault movement at crack" have been used more or less curred within a radius of 100 miles depth did cause ground cracks to synonymously. However, on the from the epicenter of the earth- form locally can not be definitely basis of priority the terms "fis- quake. Ground cracks formed in eliminated. I sure" and "fracture" should be re- the flood plains of rivers, in deltas, GEOLOGIC CONTROLS I served for two types of ground and along the toes of alluvial fans. cracks of different origin. Old- They also occurred locally in low The ground cracks were re- ham (1899, p. 86) proposed the use I terraces adjacent to flood plains, in stricted to areas underlain by un- ? of the term "fissure" for ground highway and other fill material, consolidated deposits (see fig. 2) cracks formed by forces acting at along the margins of lakes, along where one or more of the follow- the surface, and the term "frac- the face of steep slopes of river ing conditions existed : (1) perma- ture" for ground cracks formed by bluffs and hillsides, and in areas frost was absent or deep lying, (2) forces acting at depth, such as cleared of vegetation. the ground-water table was near movement along a buried fault. The overall distribution pattern the surface, (3) bedrock was rela- In many places it would obviously of ground cracks within the area tively deep lying, and (4) slopes be difficult to distinguish between of study indicates that the cracks were steep. Because the earth- the two types of ground cracks. were not localized in regional quake occurred in March, there 221-693 0-66--3 El2 ALASKA EARTHQUAKE, MARCH 27, 1964

Base from Anchorage, World (N Amenca) 1 1 000 000 scale, complied by Army Map Service

EXPLANATION • Area where ground cracks were observed, July 1964

0 10 20 30 40 I'-1 1LES

7.-Distribution of ground cracks in the Copper River Basin area. EFFECTS IN THE COPPER RIVER BASIN AREA El3 was a variable thickness of sea- tion for the longest period of time. occurred, include hillsides, lake- sonal frost throughout the area. When the earthquake occurred shores, river bluffs, and terrace Most ground cracks occurred in in the latter part of March, sea- escarpments. coarse-grained unconsolidated de- sonal frost, which was near its posits, but some occurred in fine- annual maximum penetration, LITTLE TONSINA RIVER SITE grained deposits, generally in formed a thin, brittle layer extend- The Little Tonsina River land- proximity to steep slopes, along the ing from the surf ace of the ground slide site (fig. 8, next page) is in shores of lakes, or in areas cleared to variable depths, depending the southern part of the area, on of vegetation for several years. upon local conditions. The Where well-drained unconsoli- ground motion, where it was in- the southwestern side of the dated deposits were thin, over- tense, broke this brittle layer, and Richardson Highway at mile 65. lying bedrock at shallow depths, thereby formed the ground cracks. Landsliding occurred along the grounds cracks generally did not At many places along slopes (un- northwestern side of a small hill form. confined faces), the seasonal frost underlain by unconsolidated silt, Permafrost which extends from probably prevented ground break- sand, and gravel deposits. Lateral near the surf ace to depths as great age, whereas in flat-lying areas un- movement of segments of the hill as 200 feet is widespread in the derlain by permafrost-free water- toward the northwest caused sev- Copper River Basin area, but gen- saturated materials, the seasonal eral large ground cracks to form erally was absent in areas under- frost facilitated ground breakage. on and parallel to the face of the lain by coarse-grained deposits in In most areas where severe hill and pressure ridges to develop which ground cracks formed (see ground breakage occurred, the on the floor of the Little Tonsina figs. 2, 7). Permafrost generally ground-water table was no more River valley (fig. 9). One of the was absent also near large deep than 15 feet from the surface, and large ground cracks formed by the lakes, and consequently, ground generally just a few feet. In some lateral extension of materials to- cracks occurred locally along the places, large concentrations of va- shores. In areas where ground dose water were perched on top of ward an u,nconfined face (hillside) cracks fonned in fine-grained de- the impervious permafrost. In is shown in figure 10, and a pres- posits, the impervious permafrost areas where the ground-water ta- sure ridge developed in front of table generally was from 10 to 20 ble was within a few feet of the the slide area is shown in figure 11. feet below the surface; in flat-ly- surface, permafrost generally was The horizontal forces that formed ing areas this situation permitted a absent; in areas where vadose wa- the ridge were transmitted water-saturated zone to exist be- ter was perched on top of perma- through a layer of seasonally tween the pemnafrost table and the frost, the permafrost table was 4- frozen peat and silty sand, approx- base of the seasonal frost at the atively deep lying. Under both imately 2 feet thick, overlying surface. conditions the unconsolidated de- water-saturated silty sand. Lo- The effect of permafrost on the posits beneath the seasonal frost cally, water-saturated silty sand distribution of ground cracks be- were saturated with water, and was ejected to the surface through comes apparent if one considers consequently, were subjected to cracks in the seasonally frozen that a thick layer of ice-rich per- greater intensity and duration of layer. mafrost behaves more like bedrock ground motion than unconsoli- OTHER LANDSLIDE SITES than like unconsolidated deposits dated deposits perennially frozen and that, according to Gutenberg or those not saturated with water. Other landslides include a large (1956, 195'7)) the intensity and In many parts of the area, one at the mouth of Klutina Lake duration of ground motion at the ground cracks formed on or near which caused the Klutina River to same distance from the epicenter a steep slope, which provided an be diverted, several small ones may be 10 times as great in wate,r- unconfined face for the lateral ex- along bluffs of the major rivers of saturated unconsolidated deposits tension of materials. These the area, and numerous small as in crystalline bedrock. Nat- ground cracks generally paralleled slides marginal to lakes (see fig. urally, other conditions being the slope and occurred either on 7) . Ground cracks formed along equal, ground breakage will be the face of the slope or behind it. margins of lakes by lateral move- most severe in areas receiving the Landforms with relatively steep ment of materials. An example is greatash intensity of ground mo- slopes, along which ground cracks shown in figure 12 (p. 16). ALASKA EARTHQUARE, MARCH 2 7, 19 64

8. Sketch rnap of the Little Tonsina River landslide site.

9.-View, to the northwest, showing pressure ridges on floor of Little Tonsina River valley near mile 65, Richardson Highway; pressure ridges (indicated by arrows) caused by landsliding on face of hill. EFFECTS IN THE COPPER RIVER BASIN AREA

10.-One of several large ground cracks paralleling northwest side of small hill near mile 65, Richardson Highway. Crack, formed in fine- to medium-grained sand, has maximum width of 3 feet and depth of abut 5 feet. The laterd exten- sion of materials down the side of the hill caused the ground cwcks and also caused pressure ridges to form on level ground several hundred feet in front of the base of hill.

11.-Pressure ridge, 6 feet high, on flat surface bordering Little Tonsina Ever' near mile 65, Richardson Highway. Crest of ridge broken irregularly by upward flexing of frozen peat caused by landsliding on a nearby hillside. ALASKA EARTHQUAKE, MARCH 2 7, 1 9 64

12.-Large ground crack formed in clearing along south shore of lake about two- tenths of a mile north of mile 158, Glenn Highway. Maximum width of crack is 4 feet and depth is 6 feet. This ground crack is one of several that generally parallel the lakeshore. EFFECTS IN THE COPPER RIVER BASIN AREA El7

13.-View, to the east, of the large braided flood plain of the Xelchina River 8 miles north of the terminus of the Nelchina Glacier.

NELCHINA RIVER OUTWASH during the earthquake. One of area. The delta is approximately APRON the most significant- characteristics 21h,e miles wide at its widest point The Nelchina River outwash of this site was the absence of any and generally is underlain by silty apron, in the southwestern part of unconfined face toward which the sand and gravel. Undoubtedly, the area, is underlain by silty sand materials could move, and conse- finer grained deltaic deposits are and gravel, is approximately 10 quently, form ground cracks. An present at depth. All of these de- miles in length, and averages about explanation for the origin of posits are free of permafrost, and ground cracks in such flat-lying 2 miles in width (fig. 13). the ground-water table is within a The areas is given below on page E23. unvegetated parts of this outwash few feet of the surface. Extensive Extensive ground breakage, ground breakage in the delta in- apron were literally crisscrossed similar to that in the Nelchina with ground cracks that generally cluded a concentration of cracks River outwash apron, also oc- along, and generally parallel to, a ranged from 1 to 2 feet in width curred in the flood plains of the and extended for great distances hingeline that crossed the delta. lower parts of the Chitina and This hingeline is conspicuous in across the flood plain (fig. 14, next Copper Rivers, and, locally, in page). Measurement of the rather figure 15 because most of the snow flood plains of other streams (see co-cer on the downslope side has systematic reticulate pattern of fig. 7). ground breakage at several points been removed by water and sedi- suggested a preferred orientation NELCHINA RIVm DELTA ment ejected from ground cracks. of N. 35" W. and N. 50" E. Silty The Nelchina River delta (figs. Figure 16 shows ground cracks in sand, locally including pebbles, 15-17, p. 19-21) is along the the central part of the hingeline, and large quantities of water were northwestern side of Tazlina Lake and figure 17 shows cracks at the ejected from many of the cracks in the southwestern part of the northern end of the delta. ALASKA EARTHQUAKE, MARCH 27, 1964

14.-Typical ground crack in outwash 'apron of Nelchina River 2 miles north of terminus of Nelchina Glacier; crack about 2 feet wide at widest point. Note how crack was deflected slightly in crossing swale in foreground. Standing water in swale marks the shallow ground-water table. Dark line behind man is trace of intersecting crack. I EFFECTS IN THE COPPER RIVER BASIN AREA El9

15.-The Nelchina River delta. Hingeline across the delta is conspicuous because,.most of the snow has been removed from the downslope side by water and sediment ejected from ground cracks. The pocrition and character of the water-delta interface or shoreline in 1948 compared with the postearthquake shoreline indicate that large segments of the delta front slid into the lake. IJhotograph by U.S. Coast and Geodetic Survey, April 10,1964. E20 ALASKA EARTHQUAKE, MARCH 2 7, 19 64

16.-Ground cracks along and paralleling hingeline on Nelchina River delta. Photograph by U.S. Geological Survey, October 1964. The available evidence suggests that the delta surface subsided- the greatest amount of subsidence occurring at the front of the delta and progressively lesser amounts upslope from the front. This dif- ferential subsidence resulted in a broad cambering of the delta sur- face which caused the concentra- tion of tension cracks along the hingeline. The position and character of the water-delta interface in 1948 as compared with the position and scalloped character of the post- earthquake interface (see fig. 15) indicate that not only was there subsidence but that large segments of the delta front slid into the lake. This sublacustrine landsliding generated large waves that se- verely fractured the ice on the northern part of the lake and 17.-North end of the large Nelchina River delta along the western shore of Tazlina stranded large of ice above Lake. Nwte the reticulate pattern of ground cracks which are as much as 6 feet water level along the shore. Large wide. quantities of sediment and ice were discharged through the outlet of the lake into the channel of Taz- lina River. Similar sublacustrine landsliding occurred off the fronts of deltas in Klutina Lake and in Tonsina Lake. The flooded ddta of Kiana Creek along the eastern shore of Tazlina Lake is shown in figure 18. Subsidence, probably caused by compaction of unconsolidated sediments, and lateral movement of materials toward the lakeshore caused flooding of the delta and the formation of numerous ground cracks. A large area along the eastern shore of Tazlina Lake just south of the Kiana Creek delta was inundated (fig. 19). This area, which is part of an old alluvial- fan delta of Kiana Creek formed when the creek was a much larger stream, was subjeoted to changes 18.-View showing flooding of Kiana Creek delta along eastern shore of Tazlina similar to those that occurred at Lake. the Kiana Creek delta. E22 ALASKA EARTHQUAKE, MARCH 27, 1964

19.-Large inundated area along eastern shore of Tazlina Lake just south of the Kiana Creek delta. Lateral movement and vertical compaction of materials along lakmhore caused numerous ground cracks to form and the area to subside. Note normal beach (indicated by arrow) in the distance. EFFECTS IN THE COPPER RIVER BASIN AREA E23

A

LATERAL EXTENSION

J I / Pressure ridges Y' 1 __...../ \ ./ -- ---~-­

B

I HORIZONTAL COMPACTION

---

c

DIFFERENTIAL VERTICAL COMPACTION

20.-Diagrammatic sections showing meehanism of formation of basic types of ground cracks in unconsolidated deposits in the Copper River Basin area.

ORIGIN by repeated alternate compression steep slopes (fig. 20, section .A.). As already explained, the and dilation (in the horizontal These steep slopes · provided an ground cracks within the area of direction) of materials in Hat­ unconfined face toward which ma­ study were formed in unconsoli­ lying areas where there are noun­ terials moved laterally, and in dated deposits under a variety of confined faces ; ( 3) differential some places the movement was geologic conditions. Despite this vertical compaction, caused by the great enough to be considered diversity of local conditions, the shaking of materials that vary lat­ landsliding. Generally the cracks origin of most of the ground erally in thickness or character; formed parallel to the slope or cracks can be explained by the fol­ and ( 4) combinations of the above. unconfined face. lowing mechanisms: ( 1) lateral Figure 20 shows the mechanism of HORIZONTAL COMPACTION extension, caused by materials formation of the three basic types The term "horizontal compac­ moving toward an unconfined face of ground cracks. tion" is used in this report for the such as a lakeshore, river bluff, LATERAL EXTENSION earthquake-induced mechanism hillside, or terrace escarpment; Lateral-extension ground cracks that causes unconsolidated mate­ (2) horizontal compaction, caused occurred on and behind relatively rials to lose volume in the horizon- E24 ALASKA EARTHQUAKE, MARCH 27, 1964 tal direction, and consequently, 57), and in Japan (Imamura, hingeline formed above and paral­ causes ground cracks to form (fig. 1937, p. 75). lel to the lip of the buried valley 20, section B). In flat-lying areas DIFFERENTIAL VERTICAL COMPACTION wall-under conditions similar to those depicted in figure 20, sec­ where there are no unconfined Without detailed data it is diffi­ tion 0. faces toward which the materials cult to determine the degree to can move laterally, the very pres­ which differential vertical com­ SNOWSLIDES, ROCKSLIDES, ence of numerous ground cracks, paction contributed to the forma­ AND AVALANCHES that extend for great distances tion of ground cracks throughout Within the area, snowslides, indicates that the materials have the area ; nevertheless, in certain rockslides, and avalanches were re­ lost volume in the horizontal areas this mechanism appears to stricted to the mountains sur~ direction. have been dominant in their for­ mation. rounding the Copper River Basin. In March when the earthquake They were especially numerous in occurred, seasonal frost had pene­ In a typical bedrock-confined valley underlain by unconsoli­ the Chugach Mountains which are trated the surficial materials to a dated deposits, the 1naterials are closest to the epicenter of the earth­ depth of several feet and formed a quake. Many glaciers emanate much thinner along the margins from an extensive icefield in the hard brittle surface layer. Be­ of the valley wall than in the cen­ higher reaches of these rugged cause of the extremely cold weath­ ter of the valley. Where this con­ er in the area, the frozen surficial dition exists and where the de­ mountains. The remoteness of this vast materials were in a state of tension. posits are susceptible to vertical This frozen layer probably was compaction, the materials in the mountainous region made it im­ initially cracked by ground waves center of the valley subside more practical to make a comprehensive flexing the surface. than the materials along the valley study of the slides. However, re­ The earthquake-induced ground walls because they are thicker. connaissance flights over the area, waves must have subjected the Consequently, ground cracks form reports of slides along the Rich­ water-saturated sediments beneath generally near and parallel to the ardson Highway where it crosses the seas$mal frost to repeated alter~ valley wall. Ground cracks such the Chugach Mountains, and nate compression and dilation in as these were observed along the study of postearthquake aerial the horizontal direction, the net eastern margin of the outwash photographs of the area indicate result of these forces being hori­ apron of Tazlina Glacier and lo­ that slide activity was much zontal compaction. Large quanti­ cally along the eastern margin of greater than that in· past years ties of water and silt- and sand­ the outwash apron of Nelchina when no earthquakes occurred. sized material were ejected from Glacier. Lateral variation in the The large amount of snow and the cracks, and sediment particles texture and in void ratios of the rock debris that has cascaded onto were rearranged so that they occu­ unconsolidated deposits also can the icefield and glaciers, and, prob­ pied less space. The high mobil­ cause differential compaction. ably even more important, the ity of the fine-grained materials The broad cambering of the sur­ overall disturbance to the icefield ejected from the cracks suggests face of the Nelchina River delta will affect the regimen of the gla­ that they were liquefied sponta­ (fig. 15) and the concentration of ciers emanating from it. Accord­ neously by the ground motion. ground cracks along and parallel ing to Tarr and Martin (1912, p. Terzaghi (1950, p. 100) describes to the hingeline (fig. 16) can be ex­ 51-61), several glaciers in the spontaneous liquefaction as the plained by differential vertical Yakutat area advanced abnor­ transformation of fine sand or compaction· caused by lateral vari­ mally after the Yakutat earth­ coarse silt into a liquid state. ation in the thickness of unconsoli­ quake of 1899 because of earth­ Similar mechanisms of forma­ dated deposits. quake-induced changes in the tion have been postulated for The wedge-shaped body of del­ regimen of the glaciers. If their earthquake-induced ground cracks taic deposits was laid down over hypothesis is true, it is not unrea­ in South Carolina (Dutton, 1889, the lip of a valley wall, and the sonable to expect that some of the p. 267-268), in India (Oldham, thicker deposits toward the front glaciers in the Chugach Mountains 1899, p. 88-92), in south-central of the delta were compacted more will advance an abnormal amount United States (Fuller, 1912, p. than those toward the apex. The within the next few years. EFFECTS IN THE COPPER RIVER BASIN AREA E25

EFFECTS OF THE EARTHQUAKE ON MANMADE STRUCTURES

DAMAGE TO BUILDINGS Lee's Guide Service, a short dis­ Gulkana Airfield, at mile 120, AND ASSOCIATED STRUC­ tance north of the Glenn Highway Richardson Highway, received TURES at mile 158, was severly damaged. only minor damage, even to fragile Several large crescent-shaped items inside buildings. A few The greatest amount of damage ground cracks formed in a cleared small cracks formed in a paved to buildings, which were mostly of area adjacent and parallel to a runway and in roads, and a water wood-frame or log construction, lake. This area is underlain by pipe broke under one house. occurred within the southern half gravelly silt. A small building Chistochina Lodge, at mile 238, of the area, primarily because of was partly submerged in water Glenn Highway, had no signifi­ proximity to the epicenter of the when the ground upon which it cant damage; even glasses on a earthquake. Within this part of was erected moved laterally to­ the area, breakage of fragile items shelf did not tip over. ward the lake. When the ground Tsina Lodge, at mile 34.5, Rich­ inside buildings was widespread. cracks opened, water was ejected However, major structural dam­ ardson Highway, in the southern to the surface and flowed down the age to buildings was restricted to part of the area of study had no gentle slope to the lake. localities where the intensity and major structural damage. How­ Glennallen, whose center is at duration of ground motion was ever, a few fragile items inside the mile 186, Glenn Highway, near the greatest. building were broken, and many southern junction of the Glenn and The following descriptions of loose items were moved. Richardson Highways, is the Tonsina Lodge, at mile 79, Rich- damage to buildings and associ­ largest community in the area. ardson Highway, had minor struc­ ated structures at various sites Brea,kage of fragile items inside tural damage; a fireplace and 2 within the area were selected to buildings was widespread, but chimneys were cracked severely, give a representative picture of structural damage to buildings windows were broken, walls the range of damage: generally was not severe. cracked, and some differential set­ Sheep Mountain Inn, at mile A 5-unit motel, a barracks-type tlement o c c u r r e d. Numerous 113, Glenn Highway, is on the toe building, and a trailer house were fragile items inside the building of an alluvial fan at the base of shaken oft' their foundations. The were broken. Sheep Mountain. Several ground foundation of the elementary cracks, oriented in a general east­ school building also was severely DAMAGE TO HIGHWAYS \test direction andoparalleling the damaged. S ever a 1 relatively AND BRIDGES t(')e of the fan, formed in the small ground cracks formed in Along the Glenn Highway from cleared area where the buildings cleared areas and locally damaged the Matanuska Glacier at the west­ were located. The ground move­ structures. At the Copper Valley ern edge of the area of study to ment caused severe damage to un­ Electric Co. station, damage to the junction of the Glenn and derground pipes, a small cabin was the plant foundation, flooring, and Richardson H i g h w a y s near shaken off its foundation, and equipment caused a power disrup­ Glennallen, several small cracks other buildings shifted position. tion for a little more than 4 hours formed in the pavement, and at a A diesel engine was shaken off a while repairs were being made and few places minor slumping of concrete slab to which it was generating equipment was being roadcuts occurred. The majority bolted. checked. The Glennallen Road of these cracks were less than 6 Tazlina Glacier Lodge, at mile Camp of the Alaskl} Department inches wide, and no major differen­ 156, Glenn Highway, had only of Highways, the largest installa­ tial movement took place. From minor damage. There was cori.sid­ tion in GlennaTien, sustained dam­ the junction north along the Glenn erable breakage inside, however, age to underground sewers, steam Highway, only a few small cracks and most loose objects shifted and water lines, well casings, win­ formed in the pavement-none position. dows, and a boiler. that required major repair. E26 ALASKA EARTHQUAKE, MARCH 27, 1964

No damage was reported along the Lake Louise Road which ex­ tends from about mile 160 on the Glenn Highway to the southern end of Lake Louise, a distance of 19 miles. Along the Richardson High­ way, however, serious road dam­ age occurred at several places be­ tween mile 27 near the southern edge of the area of study and mile 91 near the junction of the Rich­ ardson and Edgerton Highways. A large crack formed in the road­ way at mile 28 near Worthington Glacier, and severe road damage occurred along a 22-mile segment between mile 64, 1 mile south of the Little Tonsina · River bridge, and mile 86 near the Rock Creek bridge. Cracks as wide as 8 inches 21.-View, to the southeast, showing· the pavement surface of the Richardson formed in the pavement, and 30- Highway just south of the Little Tonsina River bridge at mile 65. Note the 8-inch to 50-foot segments of the road­ horW:ontal offset of the centerline; vertical displacement is as much as 3 inches. bed were moved differentially (fig. 21) . This differential movement was caused by Jandsliding which occurred in unconsolidated depos­ its on steep s~opes near the high­ way. The Little Tonsina River bridge also was damaged primar­ ily by this landsliding (fig. 22). At mile 79.8 the slump of a long segment of the roadbed on a side­ hill cut restricted vehicles to one­ way traffic. At mile 86.1 just north of Rock Creek a small crack formed in an abandoned section of road, and therefore, the feature was we11 preserved. Because of the granular nature of the under­ lying materials and because of the high ground-water table, the earthquake-induced ground mo­ tion caused silt and fine sand along with water, to be ejected' from the crack onto the road sur­ face (fig. 23). Only a few small 22.-Landslide movement on a hillside approximately two-tenths of a III'ile away cracks formed in the pavement and caused the Little Tonsina River bridge to be shoved from the right to the left. Minor slumping oc.C'UITed in road fill to the left of the bridge. Immediately after road fill along the Richardson the earthquak;e the pavement was buckled more than 3 feet high at the left end Highway north of mile 91. of the bridge. EFFECTS IN THE COPPER RIVER BASIN AREA :E27

Snowslides covered the Rich­ ardson Highway near mile 38, mile 39, and mile 42, and a rockslide blocked the road near mile 44; a large snowslide near mile 50 dammed the Tiekel River, and be­ cause of the danger of flooding the highway, explosives were used to blast a channel in the slide. Ice jams on the Tonsina River near mile 75 and mile 78.5 caused the river to rise and to erode highway fill near mile 76 and mile 77; ex­ plosives were used to remedy this condition also. Between mile 66 and mile 73, accelerated surface drainage from the steep mountain slope paralleling the highway on the east caused large icings to form on the highway. The Edgerton Highway was damaged very little, except for a 200-foot landslide on the Lower Tonsina Hill, a short distance north of Lower Tonsina. The 23.-Small crack across abandoned section of road on a low gravel terrace adjacent Lower Tonsina River bridge, to Rock Creek at mile 86.1, Richardson Highway. Note the fine sand and silt along which was shifted about 6 inches to both sides of the crack. the southeast, sustained consider­ able structural damage.

REFERENCES

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U.S. GOVERNMENT PRINTING OFFICE: 1966 0-221~93