STATE OF ALASKA

DEPARTMENT OF NATURAL RESOURCES

DIVISION OF GEOLOGICAL AND GEOPHYSICAL SURVEYS

Steve Cowper, Governor

Judith hi. Brady, Commfsswner

Robert 13. Forbes, Director and State GeologQt

June 1988

Thu report b a preliminary publication of DOGS. The author h oolely repponuile for its oontent and wl appreciate candid oommentr on the accuracy of the dab as well as ruggertionr to improve tbe report.

Report of Investigations 88-9 RECENT GLACIER-VOLCANO INTERACTIONS

ON MT. REDOUBT, ALASKA

b Y Matthew Sturm, Carl S. Benson,

and Peter MacKeith

STATE OF ALASKA Department o f N a t u r a l Resources

DIVISION OF GEOLOGICAL & GEOPHYSICAL SURVEYS

According t o Alaska S t a t u t e 41, t h e Alaska D i v i s i o n of Geo log ica l and Geophysical Surveys is charged w i t h conduc t ing ' g e o l o g i c a l and geophys ica l s u r v e y s t o de te rmine t h e p o t e n t i a l of Alaskan l a n d f o r p r o d u c t i o n of m e t a l s , m i n e r a l s , f u e l s , and geo the rmal r e s o u r c e s ; t h e l o c a t i o n s and s u p p l i e s of ground w a t e r and c o n s t r u c t i o n m a t e r i a l s ; t h e p o t e n t i a l g e o l o g i c h a z a r d s t o b u i l d i n g s , r o a d s , b r i d g e s , and o t h e r i n s t a l l a t i o n s and s t r u c t u r e s ; and s h a l l conduct such o t h e r s u r v e y s and i n v e s t i g a t i o n s a s w i l l advance knowledge of t h e geology o f Alaska. '

I n a d d i t i o n , t h e D i v i s i o n of G e o l o g i c a l and Geophysical Surveys s h a l l c o l l e c t , r e c o r d , e v a l u a t e , and d i s t r i b u t e d a t a on t h e q u a n t i t y , q u a l i t y , and l o c a t i o n of underground, s u r f a c e , and c o a s t a l w a t e r of t h e s t a t e ; p u b l i s h o r have p u b l i s h e d d a t a on t h e w a t e r of t h e s t a t e and r e q u i r e t h a t t h e r e s u l t s and f i n d i n g s of s u r v e y s of w a t e r q u a l i t y , q u a n t i t y , and l o c a t i o n be f i l e d ; r e q u i r e t h a t wa te r -we l l c o n t r a c t o r s f i l e b a s i c w a t e r and a q u i f e r d a t a , i n - c l u d i n g b u t n o t l i m i t e d t o w e l l l o c a t i o n , e s t i m a t e d e l e v a t i o n , w e l l - d r i l l e r ' s l o g s , pumping t e s t s , f low measurements, and w a t e r - q u a l i t y d e t e r m i n a t i o n s ; a c c e p t and spend f u n d s f o r t h e purposes of t h i s s e c t i o r i , AS 41.08.017 and 41.08.035, and e n t e r i n t o agreements w i t h i n d i v i d u a l s , p u b l i c o r p r i v a t e a g e n c i e s , communities, p r i v a t e i n d u s t r y , and s t a t e and f e d e r a l a g e n c i e s ; c o l - l e c t , r e c o r d , e v a l u a t e , a r c h i v e , and d i s t r i b u t e d a t a on s e i s m i c e v e n t s and e n g i n e e r i n g geology of t h e s t a t e ; and i d e n t i f y and inform p u b l i c o f f i c i a l s and i n d u s t r y abou t p o t e n t i a l s e i s m i c h a z a r d s t h a t might a f f e c t development i n t h e s t a t e .

~ d m i n i s t r a t i v e f u n c t i o n s a r e performed under t h e d i r e c t i o n of t h e Direc- t o r , who m a i n t a i n s h i s o f f i c e i n Fa i rbanks . The l o c a t i o n s of DGGS o f f i c e s a r e l i s t e d below:

.794 U n i v e r s i t y Avenue .400 Willoughby Avenue ( S u i t e 200) (3rd f l o o r ) F a i r b a n k s , Alaska 99709 Juneau, Alaska 99801 (907)174-7 147 (907)465-2533

.3700 A i r p o r t Way ,18225 F i s h Hatchery Road F a i r b a n k s , Alaska 99709 P.O. Box 772116 (907)451-2760 Eagle R i v e r , Alaska 99577

(907) 696-0070

T h i s r e p o r t i s f o r s a l e by DGGS f o r $3.50. DGGS p u b l i c a t i o n s may be in - s p e c t e d a t t h e f o l l o w i n g l o c a t i o n s . Mai l o r d e r s shou ld be addressed t o t h e F a i r b a n k s o f f i c e .

.3700 A i r p o r t Way .400 Willoughby Avenue F a i r b a n k s , Alaska 99709 (3rd f l o o r )

Juneau, Alaska 99801

.U.S. G e o l o g i c a l Survey . I n f o r m a t i o n S p e c i a l i s t P u b l i c I n f o r m a t i o n O f f i c e U.S. Geo log ica l Survey 701 C S t r e e t 4230 ~ n i v e r s i t ~ Dr ive , Room 101 Anchorage, Alaska 99513 Anchorage, Alaska 99508

CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . 1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 1 Methods.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Photogrammetry ..................................................... 5 Precision surveying. ............................................... 5 Snow pits and cores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Results................................................................ 6 ......................................................... Chronology 6 Mass balance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ........................................................... Dynamics 11

Discussion and conc lus ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 ......................................................... Acknowledgments 17 References cited......................................,................ 17

FIGURES

Figure 1. Drift Glacier, Mt. Redoubt, Alaska, showing study area and zones referred to in text.........................

2. Map compiled from aerial photographs, showing erosional and depositional features left on the Drift Glacier from j8okulhlaups and eruptions of Mt. Redoubt between 1966 and 1986.... .............................

3a-d. Oblique aerial photographs of the Drift Glacier, showing destruction and regeneration of glacier in Upper Canyon ..........................................

4a-f. Vertical aerial photographs of the Lower Canyon and Piedmont Lobe of Drift Glacier, with map of wave front locations between 1975 and 1982....................... 8

5. Plots of surface velocity and ice thickening at staked locations on the Piedmont Lobe of Drift Glacier....... 13

6 . Longitudinal surface profiles of the Lower Canyon and Piedmont Lobe of Drift Glacier........................ 14

RECENT GLACIER-VOLCANO INTERACTIONS ON MT. REDOUBT, ALASKA

1 by 2 Matthew Sturm , Carl S. Benson , and Peter MacKeith 3

ABSTRACT

Mt. Redoubt, a volcano located west of Cook Inlet, Alaska, eruptedplost recently from 1966 to 1968. This eruptive cycle removed about 5.7 x 10 m3 of glacier ice from the upper part of the Drift Glacier and decoupled it from the lower part in a sequence of j8kulhlaups that originated in the crater of Mt. Redoubt and flooded the Drift River. The eruptions blanketed the lower part of the glacier with sand and ash, reducing ice ablation. Normal snow- fall, augmented by intense avalanching, regenerated the upper part of the glacier by 1976, 8 yr after the last eruption. When the regenerated segment connected with the rest of Drift Glacier, a kinematic wave of thickening ice was triggered, and surface velocities accelerated in the lower part of the glacier. Surface velocities increased by an order of magnitude, and thicken- ing of 70 m or more occurred in the lower part. At the same time, upper parts of the glacier thinned by 70 m. These events advanced the glacier along its lateral margins, and threatened to cause an advance of the terminus. Had this occurred, the Drift River would have been dammed, and an unstable, ice-dammed lake would have been created, posing a catastrophic flood hazard for the oil-tanker terminal located downstream. However, the glacier appears to be returning to pre-eruption equilibrium.

INTRODUCTION

Mt. Redoubt (3,108 m), located 175 km southwest of Anchorage, is one of more than 40 active volcanoes in Alaska. It is an isolated stratovolcano located on the west side of Cook Inlet. Heavy precipitation on the volcano feeds over 10 distinct glaciers that radiate from the summit region. The youthful volcano is not heavily dissected by valleys, and the glaciers form an ice-cap complex described by Vinogradov (1981) as the atrio-valley glacier type. The 'Drift Glacier' (unofficial name), which flows from the Summit Crater, is the largest, most deeply incised glacier on the volcano. It has complex geometry, including steep icefalls over large cliff bands at the con- fluence of its two main branches. For convenience in this discussion the glacier has been divided into six zones (fig. 1). Intense avalanching and trapping of wind-blown snow in the summit crater and deep canyons through which the Drift Glacier flows create a vigorous system with high ice flux. The Drift River flows past the terminus of the glacier in a narrow gorge with ice on one side and steep rock walls on the other.

l~eo~h~sical Institute, University of Alaska, Fairbanks, Alaska 99775 (current address: U.S. Army Cold Regions Research and Engineering Laboratory, Ft. Wainwright, Alaska 99703-7860). 2~eophysical Institute, University of Alaska, Fairbanks, Alaska 99775. '~eceased (formerly of Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775).

Zone where avalanche accumulation is high

--- Equilibrium Line (approximate) Location and Nuamber of

z+ Movement Stake

A Triangulation Station - Glacier Margin Glacier Margin

g Snow Plt Location

KILOMETERS

Figure 1 . Drift Glacier, M t . Redoubt, Alaska, showing study area and zones referred to i n text . The Drift River flows past the terminus from west to east .

M t . Redoubt has a h i s t o r y of vigorous e r u p t i v e events accompanied by massive l a h a r s . The voluminous l a h a r d e p o s i t s i n the Crescent River Valley on the south s i d e of M t . Redoubt were formed about 3,500 y r ago. P r e h i s t o r i c l a h a r s a l s o b u i l t depos i t s on the no r th s i d e of M t . Redoubt i n t he D r i f t River f loodpla in ; t h i s i s where the most r ecen t (1966-1968) l a h a r s occurred (Riehle and o t h e r s , 1981). Meltwater from t h e g l a c i e r s on M t . Redoubt f a c i l i t a t e s t he formation of l a h a r s , and a t t h e same time the g l a c i e r s undergo pe r tu rba t ions during e rup t ions which may cause dynamic changes which p e r s i s t f o r decades before a new equi l ibr ium is e s t a b l i s h e d (Sturm and o t h e r s , 1986). The h i s t o r i c record , probably incomplete, l is ts e rup t ions of M t . Redoubt i n 1778, 1819, 1902 ( l a r g e explos ion with voluminous ash e j e c t a ) , 1933, and most r ecen t ly , an e rup t ive cyc le from 1965 t o 1968 (Simkin and o the r s , 1981; Riehle and o t h e r s , 1981).

The most recent e rup t ive cyc le had profound e f f e c t s on the D r i f t Glac ie r i n 1966: voluminous steam and ash e rup t ions produced a jukulhlaup from j u s t below the summit c r a t e r (Post and Mayo, 1971). Other jvkulhlaups, inc luding a l a r g e one on February 4 , 1966, occurred between 1966 and 1968 (John Finch, personal commun., 1983). Aer i a l photographs taken a f t e r t h e jBkulhlaups i n 1968 show deeply inc i sed g u l l i e s , l a r g e moul in l ike ho le s , and cauldron-shaped co l l apse f e a t u r e s i n the i c e . D e l t a i c sediment d e p o s i t s o r i g i n a t i n g from ice- tunnel e x i t s can be d i s t i ngu i shed c l e a r l y i n the photographs ( f i g . 2). Water r e l ea sed during the jukulhlaups apparent ly t r ave l ed over t h e su r f ace and through tunnels i n o r under D r i f t G lac i e r , s p i l l e d out over t he terminus, and flooded t h e D r i f t River. A jvkulhlaup on January 25, 1966 flooded the s i t e on Cook I n l e t a t the mouth of D r i f t River where an o i l - t anke r te rmina l is now loca ted ; t h i s forced t h e evacuat ion of a se i smic crew (Anchorage Daily News, 1966; Riehle and o the r s , 1981). The f lood c a r r i e d l a r g e icebergs and deposi ted a heavy mantle of sand and a sh , over 5 m t h i c k i n p laces , on the Piedmont Lobe of t h e g l a c i e r .

We es t imate from examination of a e r i a l photographs t h a t over 7 5.7 x 10 m3 of i c e was b l a s t e d , melted, scoured, o r washed away by the cumu- l a t i v e events of 1966-68. Most i c e l o s s occurred i n t he upper canyon, where l a r g e g l a c i e r s e c t i o n s were removed and bedrock was exposed; so l i t t l e i c e remained t h a t one branch of t h e g l a c i e r was e s s e n t i a l l y removed ( f i g . 2) . Large co l l apse f e a t u r e s and deep g u l l i e s scoured i n t o the su r f ace of t he remaining p a r t s of t he g l a c i e r suggest t h a t 'bo th mel t ing ( subg lac i a l and su r f ace) and eros ion ( the j bkulhlaups were heavi ly charged wi th sand and deb r i s ) were involved. These processes disconnected the lower p a r t of D r i f t Glac ie r from i c e flowing out of t h e Upper Canyon and Summit Cra t e r , causing a major reduct ion i n t he t o t a l f l u x moving through t h e Lower Canyon and Piedmont Lobe. A s i m i l a r phenomenon occurred on the Shoes t r ing Glac ier when Mount S t . Helens erupted (Brugman and Meier, 1981).

Regeneration began immediately a f t e r t he e r u p t i v e cyc l e , and t h e process was e s s e n t i a l l y completed by 1976. The amount of i c e accumulated dur ing t h i s rebui ld ing s t a g e apparent ly exceeded t h a t which had been removed by t h e erup- t i on . When r ebu i ld ing w a s complete and t h e regenerated g l a c i e r connected with t h e lower p a r t of t h e g l a c i e r , t h e increased i c e f l u x produced a bulge of t h i c k e r i c e t h a t moved down through t h e lower g l a c i e r a s a kinematic wave a t speeds f a s t e r than the normal surface-flow speeds. ( 'Kinematic wave'

J

LEGEND

I( Flood channels Areas where majority of ice was removed between 1966 and 1968

$~y.\ Thick flood deposits of sand, \.:::-.. ;.$J left as large flat terraces !.$':. Flood deltas < Ice tunnel entra ? Uncertainty in location or

extent

$ Large kettle holes

& Lava dome Pre-eruption up-glacier llmit

. of debris-covered Ice @ Ogives (1968-

*

Figure 2. Map compiled from aerial photographs, showing erosional and depositional features left on the Drift Glacier from jtrkulhlaups and eruptions of Mt. Redoubt between 1966 and 1968.

refers here to the general class of waves that result because changes in flux necessitate changes in thickness and velocity.)

Following the development of kinematic-wave theory by Lighthill and Whitham (1955), there have been a number of theoretical applications to gla- ciers, beginning with Nye (1960) and summarized by Paterson (1981). Theory has developed more rapidly than field observation, because kinematic waves are difficult to observe on glaciers. Paterson (1981) cited three examples of glacial movement phenomena that appeared to be kinematic waves. The Drift Glacier provides a fourth example.

METHODS

Three methods have been used to investigate the glacier-volcano events on Mt . Redoubt .

Photogrammetry

Ground-control points for aerial photogrammetry were surveyed in 1977 and 1978. Vertical aerial photographs were taken of Drift Glacier in 1977, 1978, 1979, and 1982. Photogrammetric maps at a scale of 1:10,000 and con- tour interval of 5 m were made from these controlled aerial photographs. From these maps, and from existing USGS maps based on photographs taken in 1954, we prepared longitudinal surface profiles of the glacier accurate to 22.5 m, and computed recent changes in thickness and volume of the glacier.

Over 120 oblique and vertical aerial photographs of Drift Glacier taken between 1938 and 1984 were examined to compile a recent glacier-volcano history. The photographic history was supplemented by interviews with eye-witnesses of the 1966-68 eruptions of Mt. Redoubt, including people who witnessed the jUkulhlaups on Drift River and colleagues who studied the erup- tion (Wilson and others, 1966; Wilson and Forbes, 1969).

Precision Surveying

A stake network (fig. 1) was established in 1978 so we could measure surface flow on the Piedmont Lobe of Drift Glacier. It was surveyed one to four times a year between 1978 and 1986. The stakes, made of 3-m lengths of pipe set in cairns on the thick supraglacial debris, were placed in four rows (A-D). They required little maintenance because there was little ablation or surface disturbance. The D row was an. exception; it survived less than a year because of heavy crevassing and ablation. A fifth row of stakes (Z) was added between the A and B rows in 1982, for more complete coverage. The stakes were located by triangulation. Survey errors in horizontal position have not exceeded f0.2 m. Errors in vertical position, mainly due to refrac- tion, have not exceeded 20.5 m.

Snow Pits and Cores

A pit 4 m deep with a core to 10 m was excavated in the Summit Crater in 1977, and in 1985 a second pit with a 26-m core was completed. Pit studies were conducted in 1983 in the East Basin; analysis of these pits and cores,

together with the ablation measurements made in 1978, have enabled us to estimate the mass-balance gradient for Drift Glacier.

RESULTS

Chronology

Figures 2, 3, and 4 illustrate melting and erosion of the Drift Glacier in the Upper Canyon during the recent volcanic eruptions and its regeneration in less than 8 yr.

The destructive phase (1966-68) occurred in three main stages:

1 . The removal of approximately 5.7 x lo7 m3 of ice eliminated ice flux from the Upper Canyon to the rest of the glacier (figs. 1 and 2) and reduced the flux through the lower glacier by more than half. Some ice that was removed became lodged or buried in the sand and ash covering the Piedmont Lobe and slowly melted out during the next few years, forming kettle holes. Most ice, however, either melted or was washed out to sea in jtlkulhlaups.

2. Approximately lo6 m2 of the Piedmont Lobe, according to estimates from vertical aerial photographs, was covered by flat terraces composed of sand and ash deposited by jtSkulhlaups and eruptions. These deposits, usually greater than 1 m thick, insulated the ice and eliminated ablation. Similar insulating effects are discussed in Muller and Coulter (1957), Driedger (1981), and Nakawo and Young (1981). Before the debris was deposited, the ablation rate on the Piedmont Lobe was about 5 m/yr, determined on the basis of 1978 measurements of bare ice cliffs at the terminus.

3. The internal and surface-water system of the Drift Glacier was pro- foundly altered by large channels and tunnels cut during the jt5kulhlaups (fig. 2). For example, water poured out from the base of the rock plug (figs. 1 and 2) that projects through the lower glacier and carved a new surface channel that persists today as one of the dominant drainages on the Piedmont Lobe.

Figures 3 and 4 illustrate how quickly the glacier re-formed in the Upper Canyon and reconnected with its lower segment:

1954-64 (figs. 3a and 4a). The condition of the glacier was 'normal,' with heavy crevassing throughout the upper parts, particularly at the confluence of the two main branches. Ogives were absent below the prominent cliffs in the confluence area.

1966-68. Eruptions and jtSkulhlaups occurred.

1968 (fig. 3b). The glacier began to re-form in the Upper Canyon.

1970 (fig. 312). Avalanching had refilled part of the Upper Canyon, but bedrock was visible at the confluence of the Upper and Lower Canyons.

Figures 3a-d. Oblique aerial photographs taken by Austin Post (1964-70) and authors (1975) showing the destruction and regeneration of the Drift Glacier in the Upper Canyon. The pointer is in the same location in each photo.

Figures 4a-f. Vertical aerial photographs (4a-e) of Lower Canyon and Piedmont Lobe of Drift ~lacier, showing pre-eruption condition of the glacier (1954) and subsequent changes caused by propagation of a kinematic wave through the system (1977-82), and a map (4f) of wave front locations between 1975 and 1982. On figure 4f, (below) dashed lines indicate where the front coincided with the terminus of the glacier, which re-formed in the Upper Canyon. Dotted lines indicate the front as manifested by the downglacier limit of new crevassing. Note the rock plug that divides the flow; cross-hatched area of the rock plug was icefree in 1977; the white and black parts of the plug were icefree in 1979, and the black part of the plug was icefree in 1982. Note also the similar appearance of the glacier in 1954 and 1982 photographs.

1975 (fig. 3d). The glacier in the Upper Canyon had re-formed. It had a steep, lobe-shaped terminus that appeared to be advancing over bedrock but was separated by 200 m from the main glacier system. Five or six ogives were present below the cliffs on the main glacier in the ice stream from the East Basin.

July 1977 (fig. 4b). The terminus of the glacier from the Upper Canyon had reconnected and advanced over the glacier in the Lower Canyon. Previously exposed areas of bedrock were covered by crevassed glacier ice. Eight ogives were noted.

September 1977 (not shown). The lobe-shaped terminus from the Upper Canyon was still recognizable but had advanced 400 m down the Lower Canyon, overriding all the ogives and nearly obliterating them.

1978-79 (figs. 4c and 4d). A kinematic wave of thickening, accelerating ice was propagating down the glacier and was accompanied by surface crevassing that progressively disrupted the sand and ash on the glacier surface and made wave movement conspicuous. Ice originating in the Upper Canyon could still be recognized in the combined ice streams of the lower glacier as a zone of clean, white ice.

1982 (fig. 4e). The kinematic wave continued to propagate through the lower glacier. Surface conditions and crevasse patterns over much of the glacier appeared similar to those in the 1954 photographs.

Mass Balance

Mass-balance measurements have been difficult to obtain, but are suffi- cient to estimate the general balance gradient for the glacier. In July, 1977, a snow pit with core to 10 m in the Summit Crater (2,590 m) did not penetrate to the 1976 summer surface; it revealed a minimum water-equivalent accumulation value of 5 m for the year. A snow pit and core to 26 m exca- vated in the Summit Crater in 1985 suggested an average balance of 6.5 m water-equivalent per yr for the 2 yr of accumulation it penetrated, although there was some difficulty in interpreting the stratigraphy. In 1983, a pit and core in the East Basin at 1,400 m penetrated more than two annual units and indicated an average annual balance of about 0.5 m water-equivalent per yr. In 1978, an ablation rate of 5 m/yr was measured at the terminus on a clean vertical ice face. By using an accumulation value of 6.5 m at the Summit Crater (2,590 m), an ablation rate of 5 m/yr at the terminus (300 m), and estimating an equilibrium-line altitude of 1,200 m from late-summer photography, we obtained a balance gradient of 0.5 m water-equivalent/100 m of altitude. This gradient is in general agreement with those of maritime Alaskan glaciers such as Wolverine and Columbia (Meier and others, 1971; Mayo, 1984), and the accumulation in the Summit Crater is in the same range as that measured on Columbia Glacier at the same altitude (Mayo, 1984).

From 1968 to 1976, when there was no ice flux out of the Upper Canyon, glacier ice rapidly accumulated there, because accumulation rates in both the Upper Canyon and the Summit Crater are high and are augmented by avalanches. Avalanching in the upper part of the canyon had covered much of the denuded

a r e a by 1970 ( f i g . 3c) . By 1975 ( f i g . 3d) , a g l a c i e r wi th a lobe-shaped terminus had re-formed i n t h e Upper Canyon and w a s w i th in 200 m of reconnect- ing wi th t h e r e s t of D r i f t Glac ie r . I n 1977, t h e reconnect ion was complete, and the regenerated lobe had a c t u a l l y overr idden p a r t of t h e g l a c i e r i n t h e Lower Canyon.

7 Between 1968 and 1976, an est imated 15 x 10 m3 of i c e accumulated i n

the Summit Cra t e r and Upper Canyon, r e c r e a t i n g t h e upper g l a c i e r . I c e volume was est imated by applying t h e balance g rad ien t of 0.5 m water-equivalent per 100 m of a l t i t u d e t o t he combined a r e a s of t h e Summit Cra t e r and Upper Canyon, and summing the 8 yea-from 1968 t o 1976.

Using the same balance g rad ien t t o e s t ima te t h e annual balance f l u x and balance v e l o c i t y through the equi l ibr ium l i n e f o r t he e n t i r e g l a c i e r , and applying the balance g rad ien t t o accumulation a r e a s

Summit Cra t e r 6

2.2 x lo6 m 2 , East Basin 3 . 8 x lo6 m 2 , Upper Canyon 3.4 x 10 m 2 ,

7 gives an annual i c e f l u x through the equi l ibr ium l i n e of 3.0 x 10 m3. I f we assume a deep, parabol ic c ros s s e c t i o n and plug flow, t he balance v e l o c i t y through the Lower Canyon i s 450 m/yr.

Dynamics

Curiously (and f o r t u i t o u s l y ) , during the time when i c e f l u x from the Upper Canyon was c u t o f f from the D r i f t Glac ie r system, t he remaining flow from the East Basin began t o form ogives below an i c e f a l l a t t he head of t h e Lower Canyon. These ogives , which formed only during t h i s per iod of t ime, can be seen i n f i g u r e 4b. In 1977, we i d e n t i f i e d e i g h t og ives , corresponding t o the 8 y r of missing f l u x from the Upper Canyon. S imi l a r ly , s i x ogives can be seen i n t h e lower l e f t corner of the 1975 photograph ( f i g . 3d). The ogives, overrun and o b l i t e r a t e d by t h e lobe of i c e from t h e Upper Canyon i n 1977-78, have not been noted s ince . They a r e a v i s i b l e man i f e s t a t ion of t h e d i f f e r e n t flow regimes t h a t ex i s t ed i n t he g l a c i e r of t h e Lower Canyon when t h e r e was no i c e f l u x from the Upper Canyon. When flow was from t h e Eas t Basin only, t he ogives i n d i c a t e an approximate su r f ace v e l o c i t y of 315 m/yr, i f one assumes t h a t they form annual ly by seasonal v a r i a t i o n i n flow. This va lue f o r t h e East Basin component i s 100 m/yr l e s s than t h e balance v e l o c i t y f o r t he e n t i r e g l a c i e r .

The speed a t which the lobe-shaped terminus of t h e regenera ted g l a c i e r advanced has been computed from photographs ( f i g s . 4a-e) t o be:

Period Rate of advance (m/yr)

1975-77 450 July-September 1977 1,200

1977-78 1,300 1978-79 520 1979-82 210

These speeds r ep re sen t t h r e e c l o s e l y r e l a t e d phenomena. Pre-1977 r a t e i s thp speed of t he terminus advancing over bedrock. Rates during 1977 and 1978, a f t e r reconnection t o the main g l a c i e r , r e f l e c t t he speed of t h e f r o n t a l lobe of over r id ing i c e . From 1978 on, however, t h i s f r o n t was obscure, and t h e r a t e s r e f l e c t t he advance of t h e downglacier edge of new crevass ing . The computed speeds were supplemented by survey d a t a t h a t recorded the onse t of i c e acce l e ra t ion and thickening a s i t passed through the s t a k e network on t h e Piedmont Lobe. The abrupt decrease i n speed of t he f r o n t between 1978 and 1979 corresponds t o the time t h a t i t moved out of t h e confined Lower Canyon. The kinematic wave propagated through D r i f t Glac ie r a t speeds t h r e e t o f i v e t imes the average su r f ace v e l o c i t y of t he g l a c i e r i n the same a rea .

Survey da t a from the s t a k e network g ive a c l e a r p i c t u r e of t h e kinematic wave of thickening i c e , accompanied by inc reas ing su r f ace v e l o c i t y , pass ing through the Piedmont Lobe ( f i g . 5 ) . Apparently, t he rock plug a f f e c t e d wave propagation, because speed and d i r e c t i o n of e a s t e r n and western segments d i f f e r e d . The rock plug has a l s o served t o i n d i c a t e i c e th ickening ( f i g . 4 f ) ; before 1979, h e l i c o p t e r s could land on i t , but i n 1982 i t was covered by i c e s e r a c s , which ind ica t ed a th ickening of over 50 m.

Surface v e l o c i t y throughout t he Piedmont Lobe was l e s s than 10 m/yr when f i r s t measured i n 1978. By 1979 the flow had begun t o a c c e l e r a t e a t t h e C row of s t akes . This a c c e l e r a t i o n progressed downglacier through t h e B and A rows a t t he r a t e of about 1 row per y r , a d i s t a n c e of about 1 km. Accelera- t i o n a t t he C row began i n 1980-81, a l though s t a k e C-1, which is loca t ed i n the western component of flow, began t o a c c e l e r a t e a s e a r l y a s 1979. Accel- e r a t i o n a t the B row began i n 1981, and a c c e l e r a t i o n a t t h e A row began i n 1982. Data f o r t he Z row, which was emplaced i n 1982, suggest t h a t acce l e ra - t i o n began the re i n 1982. Overa l l , f low speeds increased by one o rde r of magnitude o r more.

The da t a suggest t h a t by 1986 su r f ace v e l o c i t i e s had peaked and begun t o decrease a t t he C and B rows of s t akes . This impl ies t h a t t h e kinematic wave took about 5 y r t o move p a s t t he C row of s t a k e s . However, the summer veloc- i t y of D r i f t Glac ie r i s 20-25 percent g r e a t e r than i t s win te r v e l o c i t y , and a measurement taken during sp r ing o r autumn surveys could inc lude a component of the high summer-velocity component. Inc lus ion of a g r e a t e r percentage of summer-velocity component could account f o r t he 1982 v e l o c i t y peak i n B row, but i s i n s u f f i c i e n t t o account f o r t h e peak i n C row, which shows d e f i n i t e dece l e ra t ion .

The thickening which accompanied a c c e l e r a t i o n is p l o t t e d and p r o f i l e d on f i g u r e s 5 and 6 , r e spec t ive ly . Maximum th ickening , measured by surveying a t s t ake C-4, was over 40 m, a l though g r e a t e r th ickening (70 m) was measured photogrammetrically a t o the r p o i n t s on the Piedmont Lobe.

In tense c revass ing took p l ace a f t e r t he onse t of th ickening and was pre- ceded downglacier by a no t i ceab le warping of t h e f l a t sand and ash t e r r a c e s ( f i g . 2) i n t o t r ansve r se s y n c l i n a l f o l d s wi th wavelengths of t e n s of meters . The c revass ing progress ive ly d is rupted t h e t e r r a c e s . I n i t i a l l y , sma l l longi- t u d i n a l c racks formed i n t he su r f ace d e b r i s , bu t w i th in a year o r two t h e g l a c i e r su r f ace became a chao t i c jumble of c revasses and b lue f i n s of i c e .

HORIZONTAL VELOCITY

THICKENINO (+) OR THlNNlNO (-) AT STAKE / LOCATION WITH DATA POINTS SHOWN AS DOTS -7- DATA MIS81NO OR INCOMPLETE

DIRECTION OF HORIZONTAL VELOCITY AT WITH STAKE NUMBER

YEAR 1978 79 80 81 82 83 84 85 1988

~ O C N CLUO 1 4 0 - ' ' ' ' - 24 - - STAKE 8-4 E 120 - - 20 DRIFT GLACIER

PIEDMONT LOBE I -

" 100 - - 18

- - STAKE 8-3

STAKE Z-2

i Y

-4

YEAR

- STAKE C-4 200 -

180 - - 32 - 28

140 -

- 12

140- - STAKE C-3 - 20

> 100- - 18

n 24

WAKE C-2 / I 1 7 20

140- - STAKE C-1 g 120-

I - - 100 -

f > 00: - 2 eo-

0, 40- B - P 20- '

0-""" 1078 79 80 81 82 83

YEAR YEAR YEAR

Figure 5. Plots of surface velocity and ice thickening at staked locations on the Piedmont Lobe.

I150 1 I 1 I I I I

C A

(I00 - :! 4954 ----- It 1977 - -..-

1978 - 1979 ..-......... 1982 -

900 -

850 -

J W 2 750 - -I

4 W VI

w 700 - 5 0 m a VI g 650 - I- W Z

600 -

550 -

500 -

450 -

400 -

350 - Vert~cal Exaggerat~on = + O X

300 -

0

METERS

Figure 6 . Longitudinal surface p r o f i l e s of Lower Canyon and Piedmont Lobe of the Dr i f t Glacier.

The debris fell into the crevasse openings and ablation began where debris was removed. The longitudinal and radial crevasses can be seen clearly in figure 4e.

Longitudinal profiles of the glacier for the years 1954, 1977, 1978, 1979, and 1982 (fig. 6) have been extended upglacier to the icefall at the confluence of the East Basin and the Upper Canyon, which is as far as photo- grammetric control would allow. The profiles confirm steady ice thickening in the Piedmont Lobe since 1977 but also show thinning in the upper reaches at the confluence of the two glacier'branches.

The profile in the Lower Canyon was thickest in 1977 and probably indicates that the kinematic wave was passing through the canyon at that time. Thinning followed rapidly in 1978. By 1982, over 70 m of thinning had taken place at the narrowest part of the canyon, and stranded fringes of glacier ice over 50 m above the glacier surface were noted there, similar to those observed on the Variegated and Muldrow Glaciers after their surges (Harrison, 1964; Post and LaChapelle, 1971; Kamb and others, 1985).

The transition between zones of ice thinning and thickening occurs at the exit of the Lower Canyon, where the glacier begins to spread out on the Piedmont Lobe. This point of zero change in surface elevation has remained nearly stationary throughout the period for which we have data.

A simple model of prismatic volume elements based on the longitudinal profiles was used to calculate the total volume lost from thinning of the upper part of the glacier and the total volume gained from thickening of the lower part from 1978 to 1982. Effects of residual annua3 snowpack on the volumes were not considered. A total volume of 8 6 .x 10 m3 of ice was added 7 to the lower part, and a total volume of 4.0 x 10 m3 was lost from the frac- tion of the upper part covered by our maps.

DISCUSSION AND CONCLUSION

Volcanic eruptions during 1966 through 1968 reduced the flux of the lower part of Drift Glacier by more than half. Ice flux from the Upper Canyon and Summit Crater was eliminated for 8 yr. The glacier in the Upper Canyon re-formed rapidly and reconnected with the main system in 1976. The reconnection more than doubled the flux and propagated a kinematic wave through the glacier which has been observed by our surveying and photogram- metry.

The passage of the kinematic wave appears to be returning the glacier to its pre-eruption equilibrium. This can be seen by comparing photographs of the glacier before the eruption (fig. 4a) with recent photographs (fig. 4e), which show surface crevassing, thickness where ascertainable, and overall longitudinal profile to be similar to pre-eruption conditions. Note, for example, the close similarity between the 1954 and 1982 profiles in figure 6.

The regenerated glacier apparently had more mass when it reconnected than before the eruption. This is suggested (1) by our calculation that about twice as much ice accumulated in the Upper Canyon and Summit Crater

- 15 -

during t h e 8 y r of i t s r e b u i l d n g than was l o s t du r ing t h e e rup t ion , and (2) by t h e d a t a i n f i g u r e 5 , which show t h a t t h e l e v e l s t o which i c e v e l o c i t y decreased were s t i l l s i g n i f i c a n t l y h igher than before t h e i c e thickened. These c a l c u l a t i o n s suggest an i n i t i a l surge of h igher f l u x a s t h e excess mass i n t h e upper g l a c i e r was discharged immediateLy a f t e r t he reconnect ion, f o l - lowed by a s l i g h t l y reduced f l u x a s t h e system came t o equi l ibr ium.

A t t h e same time t h a t i c e was removed from t h e Upper Canyon, d e b r i s w a s depos i ted on the Piedmont Lobe, which reduced a b l a t i o n and allowed t h e i c e t o th icken , a s flow cont inu d out of t h e East Basin. Reduced a b l a t i o n c rea t ed 7 an i c e su rp lus of 7 x 10 m3 over what would have accumul t ed without t h e 3 d e b r i s cover. Thickening during t h e same time was 9 x 10 m3. However, the Piedmont Lobe must have been thickened not only by reduced a b l a t i o n , but by the passage of t he kinematic wave a s w e l l , The kinematic wave can be i d e n t i - f i e d by i t s e f f e c t s on the i c e such a s c revass ing , a s soc i a t ed l o s s of d e b r i s cover , and onse t of melt ing.

Changes i n v e l o c i t y on t h e Piedmont Lobe observed between 1979 and 1986 cannot be explained by increased i c e deformation caused by increased g l a c i e r th ickness and su r f ace s lope alone. Some change i n basa l s l i d i n g seems I i k e l y . For example, between 1981 and 1982, t h e v e l o c i t y a t s t a k e C-3 increased from 20 t o 115 mlyr. During t h e same per iod , i c e t h i ckness increased l e s s than 25 m and o v e r a l l s u r f a c e s lope increased a t most a few degrees. Assuming a conserva t ive i c e t h i ckness of 200 m, theory (Nye, 1952; Paterson, 1981) i n d i c a t e s a t most an inc rease i n v e l o c i t y of 20 mlyr. Changes i n b a s a l s l i d i n g may have r e s u l t e d from changes i n i n t e r n a l g l a c i e r plumbing a s a r e s u l t of t h e j t lkulhlaups, diminished water supply because of reduced a b l a t i o n an t h e Piedmont Lobe, o r from e f f e c t s produced by t h e kinematic wave a s i t passed.

The even t s on D r i f t G lac i e r were caused by a dramatic e x t e r n a l event--a volcanic eruption--but s t r i k i n g s i m i l a r i t i e s e x i s t between these events and those observed dur ing a g l a c i e r surge. From 1978 t o t h e p re sen t , we observed an order-of-magnitude inc rease i n s u r f a c e v e l o c i t y , a long wi th thickening and crevass ing of t h e g l a c i e r sur face . There was a n e t displacement of mass from an upper t o a lower zone of t h e g l a c i e r . On t h e b a s i s of these cha rac t e r i s - t i c s , i t would be poss ib l e t o c l a s s i f y D r i f t G lac i e r a s type I11 i n Meier and P o s t ' s (1969) system of surge g l a c i e r s . Although D r i f t Glac ie r is not con- s ide red t o be a surge g l a c i e r , i t might have some mechanisms i n common wi th surg ing g l a c i e r s .

Though the kinematic wave appeared t o be a t t e n u a t i n g by 1986, i ts pas- sage through the g l a c i e r could have c rea t ed an unexpected geo log ica l hazard. I f t h i s wave--which caused some advance of t h e g l a c i e r margin between 1982 and 1986--had caused even 25 m of terminus advance, t h e g l a c i e r would have dammed the D r i f t River and c rea t ed a glacier-dammed l ake . Varved lake sed- iments found along the D r i f t River (A. T i l l , personal commun., 1984) i n d i c a t e t h a t t h i s has happened i n t he p a s t . Ice-dammed l akes a r e uns t ab le and d i s - charge c a t a s t r o p h i c a l l y ; such a l a k e would have posed a s e r i o u s t h r e a t t o t h e o i l - t anke r te rmina l l oca t ed a t the mouth of D r i f t River.

General ly , a c t i v e volcanoes covered by g l a c i e r s pose unique geologic hazards . I n a d d i t i o n t o explos ive e rup t ions (Alaska con ta in s 90 percent of t h e exp los ive volcanoes i n t h e United S t a t e s ) , t h e mel t ing of i c e and snow on glacier-covered volcanoes can produce jakulh laups and r a p i d l y moving s l u r r i e s of water -sa tura ted mud, i c e , and rock ( l a h a r s ) . Recent examples of t h e de- s t r u c t i v e power of l a h a r s were provided by Mount S t . Helens i n 1980 and Nuevado d e l Ruiz, Colombia, i n 1985. M t . Redoubt has produced both j8kulh- laups and l a h a r s i n t h e p a s t and w i l l produce more i n t h e fu tu re . It i s l i k e l y t h a t bo th l a h a r s and j6kulhlaups r e q u i r e pre-erupt ive mel t ing of g l a c i e r i c e , ponding of mel twater , and s a t u r a t i o n of s u b g l a c i a l rock.

Pos t -e rupt ive hazards a l s o occur on glacier-volcano systems, a s pointed up by our work a t M t . Redoubt. The recovery of D r i f t G lac i e r from pe r tu r - b a t i o n s caused by t h e 1966-68 e rup t ions has taken 20 y r , and nea r ly r e s u l t e d i n a new f looding hazard 2 decades a f t e r t h e e rup t ion .

ACKNOWLEDGMENTS

This r e sea rch was supported f i n a n c i a l l y by t h e Alaska Department of Na tu ra l Resources Div is ion of Geological and Geophysical Surveys (DGGS) and by o t h e r s t a t e funds. L o g i s t i c a l support f o r t h i s work was generously sup- p l i e d by t h e Cook I n l e t Pipe Line Co., t h e U.S. Bureau of Land Management OCSEAP o f f i c e , DGGS, Nat ional Park Serv ice , and U.S. Geological Survey.

We express thanks t o Gary Bender, C. F. Benson, Ted Clarke, Jtirgen Kienle , Roman Motyka, Dan S o l i e , Betsy Sturm, and Ca r l Tobin f o r t h e i r c h e e r f u l p a r t i c i p a t i o n i n t h e f i e l d work. We a l s o thank B i l l Long and R.L. Hooke f o r t h e i r reviews of t h e manuscript.

REFERENCES CITED

Brugman, M . , and Meier, M . , 1981, Response of g l a c i e r s t o t h e e rup t ions of M t . S t . Helens, - i n Lipman, P.W., and Mullineaux, D . , eds . , The 1980 e rup t ions of M t . S t . Helens, Washington: U.S. Geological Survey Profes- s i o n a l Paper 1250, p. 743-756.

Driedger , C . , 1981, E f f e c t of a sh t h i cknes s on snow a b l a t i o n , Lipman, P.W., and Mullineaux, D . , eds . , The 1980 e rup t ions of M t . S t . Helens, Washington: U.S. Geological Survey P ro fe s s iona l Paper 1250, p. 757-760.

Har r i son , A.E., 1964, I c e su rges on t h e Muldrow Glac i e r , Alaska: Journa l of Glaciology, v. 5, p. 365-368.

Kamb, B . , Raymond, C.F., Harr ison, W.D., Engelhardt , H . , Echelmeyer, K . A . , Humphrey, N . , Brugman, M.M., and P f e f f e r , T , , 1985, G lac i e r surge mecha- nism: 1982-1983 surge of Variegated G lac i e r , Alaska: Science, v. 227, no. 4686, p. 469-479.

L i g h t h i l l , M . J . , and Whitham, B.G., 1955, On kinematic waves: Proceedings of t h e Royal Soc i e ty of London, s e r . A, v . 229, p. 281-345.

Mayo, L.R., 1984, G lac i e r mass balance and runoff r e sea rch i n t h e U.S.A.: Geograf iska Annaler, v. 66A, no. 3 , p. 215-227.

Meier, M., and Pos t , Aust in , 1969, What a r e g l a c i e r surges?: Canadian Journal of Ear th Sc iences , v. 6, no. 4, p t . 2, p. 807-817.

Meier, M., Tangborn, W.V., Mayo, L.R., and Pos t , Aust in , 1971, Combined i c e and water ba lances of Gulkana and Wolverine G lac i e r s , Alaska, and South

Cascade Glacier, Washington, 1965 and 1966 hydrologic years: U.S. Geo- logical Survey Professional Paper 715-A, 23 p., 5 sheets.

Muller, E.H., and Coulter, H.W., 1957, The Knife Creek glaciers of Katmai Na- tional Monument, Alaska: Journal of Glaciology, v. 3, no. 21, p. 116-121.

Nakawo, M., and Young, G.J., 1981, Field experiments to determine the effect of a debris layer on ablation of glacier ice: Annals of Glaciology, v. 2, p. 85-91.

Nye, J.F., 1952, The mechanics of glacier flow: Journal of Glaciology, v. 2, p. 82-93.

Nye, J.F., 1960, The response of glaciers and ice sheets to seasonal and cli- matic changes: Proceedings of the Royal Society of London, ser. A, v. 256, p. 559-584.

Paterson, W.S.B., 1981, The physics of glaciers (2d edition): Oxford, Pergammon Press, 380 p.

Post, Austin, and LaChappelle, E.R., 1971, Glacier ice: Seattle, University of Washington Press, 110 p.

Post, Austin, and Mayo, L.R., 1971, Glacier dammed lakes and outburst floods in Alaska: U.S. Geologic Survey Hydrologic Atlas HA-455, (scale 1:1,000,000) 3 sheets.

Riehle, J.R., Kienle, Jurgen, and Emmel, K.S., 1981, Lahars in Crescent River Valley, Lower Cook Inlet, Alaska: Alaska Geological and Geophysical Sur- veys Geologic Report 53, 10 p.

Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, C., and Latter, J.H., 1981, Volcanos of the world, Smithsonian Institution: Stroudsburg, Pennsylvania, Huichinson Ross P~blishing Co., 233 p,

Sturm, M., Benson, L.:., and MacKeith, P., 1986, EKfrcts of the 1966-1968 eruptions of &t. Redorlbt or1 the flow of D1.ift Glacier, Alaska, U.S.A.: Journal of Gl.aciology, v. 32, no. 112, p. 355-362.

Vinogradov, V.N., 1981, Glacier erosion and sedimentation in the volcanic regions of Kamchatka: Annals of Glaciology, v. 2, p. 164-169.

Wilson, C.R., and Forbes, R.B., 1969, Intrasonic waves from Alaskan volcanic eruptions: Journal of Geophysical Research, v. 74, no. 18, p. 4511-4522.

Wilson, C.R., Nichparenko, S., and Forbes, R.B., 1966, Evidence for two sound channels in the polar acmosphere from infrasonic observations of an Alaskan volcano: Nature, v. 211, p. 163-165.