U.S. Department of the Interior

U.S. Geological Survey

Mass Balance, Meteorology, Area Altitude 

Distribution, Glacier-Surface Altitude, Ice Motion, 

Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Water-Resources Investigations Report 03–4095
Cover: View looking north-northwest at the middle ablation zone of the main branch of Gulkana Glacier on 

August 8, 2002. The 1,480-meter weather station appears in the foreground. The main branch of the glacier starts 

out of the image to the right, then flows from right to left across the image, and finally terminates out of the image 

on the left. The icefall in the left center of the image is fed by the large western tributary of Gulkana Glacier, not 

visible here. Index site A lies just barely out of the image to the left; index site B lies in the right center of the 

image.
U.S. Department of the Interior

U.S. Geological Survey

Mass Balance, Meteorology, Area Altitude 

Distribution, Glacier-Surface Altitude, Ice Motion, 

Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

By ROD S. MARCH

Water-Resources Investigations Report 03–4095

Fairbanks, Alaska

2003
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

For additional information write to: Copies of this report can be purchased from:

Alaska Science Center U.S. Geological Survey

Chief, Water Resources Office Information Services

U.S. Geological Survey Building 810

4320 University Drive, Suite 201 Box 25286, Federal Center

Anchorage, AK 99508–4664 Denver, CO 80225–0286

http://ak.water.usgs.gov/glaciology/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.
Contents III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction ........................................................................................................................................................................... 1

Description of Gulkana Glacier Basin and Its Climate ............................................................................................... 2

Measurement System and Terminology ...................................................................................................................... 3

Data Collection ...................................................................................................................................................................... 6

Meteorology........................................................................................................................................................................... 6

Air Temperature........................................................................................................................................................... 6

Precipitation Catch ...................................................................................................................................................... 8

Wind Speed.................................................................................................................................................................. 10

Area Altitude Distribution ..................................................................................................................................................... 13

Glacier Mass Balance ............................................................................................................................................................ 14

Balance at Specific Sites.............................................................................................................................................. 14

Area-Averaged Balances ............................................................................................................................................. 18

Measured and Maximum Winter Snow Balances........................................................................................................ 20

Net Balance.................................................................................................................................................................. 20

Summer Balance.......................................................................................................................................................... 20

Annual Mass Balance .................................................................................................................................................. 20

Accumulation Area Ratio and Equilibrium Line Altitude........................................................................................... 21

Glacier-Surface Altitude........................................................................................................................................................ 21

Ice Motion.............................................................................................................................................................................. 24

Terminus Position .................................................................................................................................................................. 24

Runoff.................................................................................................................................................................................... 28

Summary................................................................................................................................................................................ 29

References Cited.................................................................................................................................................................... 30

FIGURES

1. Diagram showing the cause and effect relationships for the data presented in this report .................................... 2

2. Maps of Gulkana Glacier and vicinity .................................................................................................................... 3

3. Composite vertical photograph of Gulkana Glacier and its basin showing index-measurement sites, streamgaging station, weather station, and basin boundary, July 11, 1993 ....................................................................... 4

4–12. Graphs showing:

4. Time distribution of index-site mass balances for Gulkana Glacier, 1996 hydrologic year .................................. 5

5. Time distribution of glacier-averaged mass balance of Gulkana Glacier, 1996 hydrologic year .......................... 6

6. Daily mean air temperature recorded at 1,480-meter weather station, Gulkana Glacier Basin, 

1996 hydrologic year.............................................................................................................................................. 7

7. Daily precipitation catch recorded at 1,480-meter weather station, Gulkana Glacier Basin, 1996 hydrologic 

year......................................................................................................................................................................... 10

8. Daily average wind speed recorded at 1,480-meter weather station in Gulkana Glacier Basin, 

1996 hydrologic year.............................................................................................................................................. 11

9. Monthly average wind speed recorded at 1,480-meter weather station in Gulkana Glacier Basin for 

1996 hydrologic year.............................................................................................................................................. 12

10. Area altitude distribution of Gulkana Glacier in 1967 and 1993 ........................................................................... 13

11. Glacier-averaged measured winter balance, net balance, and summer balance, 1966–96, and smoothed data..... 21

12. Glacier-surface altitudes at index sites A, B, and D............................................................................................... 22
IV Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

FIGURES—Continued

13. Map of glacier terminus positions from Global Positioning System surveys on August 31 and September 1, 

1996, and from U.S. Geological Survey 1:63,360-scale Mt. Hayes A3 and B3 quadrangle digital raster graphic 

files ......................................................................................................................................................................... 26

14. Graph showing daily runoff from Phelan Creek near Paxson, 1996 hydrologic year ............................................ 29

15. Graph showing estimated daily runoff from Phelan Creek near Paxson, 1996 hydrologic year, with measured 

values for both 1996 hydrologic year and entire period of record ......................................................................... 31

TABLES

1. Summary of data collection in Gulkana Glacier Basin for the 1996 balance year analysis................................... 7

2. Daily, monthly, and annual average air temperatures from analog sensor recorded at 1,480-meter weather 

station, Gulkana Glacier Basin, 1996 hydrologic year........................................................................................... 8

3. Daily, monthly, and annual average air temperatures from digital sensor recorded at 1,480-meter weather 

station, Gulkana Glacier Basin, 1996 hydrologic year........................................................................................... 9

4. Daily and monthly precipitation catch recorded at 1,480-meter weather station, Gulkana Glacier Basin, 

1996 hydrologic year .............................................................................................................................................. 11

5. Daily mean wind speed from the Gulkana Glacier Basin, 1996 hydrologic year .................................................. 12

6. Area altitude distribution of Gulkana Glacier and Gulkana Glacier Basin by 100-meter altitude intervals as 

defined from a digital elevation model derived from July 11, 1993, photography................................................. 14

7. Stake, snow depth, and snow-density data for index sites A, B, and D on Gulkana Glacier, September 1995 

through April 1997 ................................................................................................................................................. 15

8. Snow-temperature, firn-thickness, and firn-density data for index sites A, B, and D on Gulkana Glacier, 

September 1995 through April 1997 ...................................................................................................................... 16

9. Ice data and mass-balance calculations for index sites A, B, and D on Gulkana Glacier, September 1995 

through April 1997 ................................................................................................................................................. 17

10. Index-site and area-integrated balance quantities for Gulkana Glacier and Gulkana Glacier Basin, 

1996 hydrologic year, from both 1967 and 1993 area altitude distributions.......................................................... 19

11. Glacier-surface and summer-surface altitude measurements and analysis at index sites, Gulkana Glacier Basin,

September 1995 to September 1996....................................................................................................................... 23

12. Continuation of glacier-surface and summer-surface altitude measurements and analysis at index sites, 

Gulkana Glacier Basin, September 1995 to September 1996 ................................................................................ 23

13. Stake locations, stake lean corrections, and motion determined from optical surveys, September 1995 to 

September 1996 ...................................................................................................................................................... 25

14. Global Positioning System terminus-position surveys at Gulkana Glacier on August 31 and September 1, 

1996 ........................................................................................................................................................................ 27

15. Daily mean runoff from the Gulkana Glacier Basin, 1996 hydrologic year .......................................................... 30
Contents V

Horizontal Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83), the North 

American Datum of 1927 (NAD 27), and to a local sea-level-based coordinate system described in detail in 

the text.

Vertical Datum

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD of 

1929), which is defined as follows: a geodetic datum, formerly called SEA LEVEL DATUM OF 1929, 

derived from a general adjustment of the first-order level nets of both the United States and Canada. In the 

adjustment, sea levels from selected TIDE stations in both countries were held fixed. The year indicates the 

time of the general adjustment. This datum should not be confused with MEAN SEA LEVEL. Altitudes are 

the same in both the local coordinate system and the Universal Transverse Mercator (UTM) system. 

Symbols Used in This Report

AAR accumulation area ratio

b area-averaged balance value

b' average stake height of the glacier surface within a 25- to 75-meter radius of the stake, in meters

b'ss1 average stake height of the first summer surface down from the glacier surface within a 25- to 75-meter radius of the 

stake, in meters

b'ss2 average stake height of the second summer surface down from the glacier surface within a 25- to 75-meter radius of 

the stake, in meters

b0' initial value (on October 1) of the height of a stratigraphic surface on the stake

b0'ss1 initial stake height at the beginning of the measurement year of the first summer surface down from the glacier surface within a 25- to 75-meter radius of the stake, in meters

b0'ss2 initial stake height at the beginning of the measurement year of the second summer surface down from the glacier 

surface within a 25- to 75-meter radius of the stake, in meters

b* stake height of surveyed point near b' on the stake, in meters

b** calculated stake height of the glacier surface directly above the stake bottom (as if the stake were vertical), in meters

bA measured mass balance at index site A, in meters

CONVERSION FACTORS, DATUMS, AND SYMBOLS

Multiply By To obtain

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

square kilometer (km2) 0.3861 square mile (mi2

)

kilogram (kg) 2.205 pound, avoirdupois (lb)

kilogram per liter (kg/L) 62.43 pound per cubic foot (lb/ft3)

kilogram per cubic meter (kg/m3) 0.06243 pound per cubic foot (lb/ft3)

meter per year (m/yr) 3.281 foot per year (ft/yr)

meter per second (m/s) 3.281 foot per second (ft/s)

millimeter per day (mm/d) 0.039 inch per day (in/d)

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

grad 0.9 degree (°)

degree Celsius (oC) 1.8, then add 32 degree Fahrenheit (°F)
VI Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

ba annual balance at site

ba area-averaged annual balance

ba(f) annual firn balance

ba(j) glacier-averaged annual internal ablation

bB measured mass balance at index site B, in meters

bD measured mass balance at index site D, in meters

bn net balance at site

bno initial net balance

bnl late net balance

bn area-averaged net balance

bs area-averaged summer balance

bw area-averaged winter balance

b(f) new firn balance at site

b(i) old firn and ice balance at site

ba(i) annual old firn and ice balance at site

b(k) internal accumulation at site

ba(k) annual internal accumulation at site

b(ls) late snow balance at site

b1(ls) final late snow balance at site

b(s) snow balance at site

b0(s) initial snow balance at site

b0(s) area-averaged initial snow balance

bm(s) measured winter snow balance at site

bm(s) area-averaged measured winter snow balance

bw(s) maximum winter snow balance at site

bw(s) area-averaged maximum winter snow balance

d(s) snow depth, in meters

d(nf) new firn depth, in meters

E UTM Easting

ELA equilibrium line altitude

EMT electrical metallic tubing

GPS Global Positioning System

Ht height of the stake upper target above the stake bottom as measured along the stake, in meters

HY hydrologic year

k horizontal scale factor between the UTM plane and sea level

k mean horizontal scale factor between the UTM plane and sea level

mwe meters water equivalent

n sample number

PLGR Precision Lightweight GPS Receiver

ss1 first glacier summer surface down from the glacier surface (this is typically glacier ice in the ablation zone and a firn 

surface in the accumulation zone)

ss2 second glacier summer surface down from the glacier surface (this is typically a firn surface; multiple summer surfaces only occur in the accumulation zone of the glacier)

UTM Universal Transverse Mercator
Contents VII

Xg local sea-level coordinate of measurement stake at glacier surface, in meters

Xi local sea-level coordinate of index site, in meters

XL local sea-level coordinate, in meters

Xs local sea-level coordinate of bottom of measurement stake, in meters

Xt local sea-level coordinate of stake upper target, a point on the stake 1.5 to 2.0 meters above the glacier surface, in 

meters

Yg local sea-level coordinate of measurement stake at glacier surface, in meters

Yi

 local sea-level coordinate of index site, in meters

YL local sea-level coordinate, in meters

Ys local sea-level coordinate of bottom of measurement stake, in meters

Yt

 local sea-level coordinate of stake upper target, a point on the stake 1.5 to 2.0 meters above the glacier surface, in 

meters

Z altitude, in meters

Zg altitude of measurement stake at glacier surface, in meters

Zi altitude of glacier surface at index site, in meters

Zi

(ss1) altitude of the first summer surface below the glacier surface at index site, in meters

Zs altitude of bottom of measurement stake, in meters

Zt altitude of stake upper target, a point on the stake 1.5 to 2.0 meters above the glacier surface, in meters

dXYZ total three-dimensional displacement of the stake bottom between measurements

θ downdip direction with zero east and positive counterclockwise

φ dip angle with zero horizontal and positive angles up
VIII Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year
Introduction 1

Mass Balance, Meteorology, Area Altitude Distribution, 

Glacier-Surface Altitude, Ice Motion, Terminus Position, and 

Runoff at Gulkana Glacier, Alaska, 1996 Balance Year

By Rod S. March

Abstract

The 1996 measured winter snow, maximum 

winter snow, net, and annual balances in the Gulkana Glacier Basin were evaluated on the basis of 

meteorological, hydrological, and glaciological 

data. Averaged over the glacier, the measured 

winter snow balance was 0.87 meter on April 18, 

1996, 1.1 standard deviation below the long-term 

average; the maximum winter snow balance, 

1.06 meters, was reached on May 28, 1996; and 

the net balance (from August 30, 1995, to 

August 24, 1996) was -0.53 meter, 0.53 standard 

deviation below the long-term average. The 

annual balance (October 1, 1995, to September 

30, 1996) was -0.37 meter. Area-averaged balances were reported using both the 1967 and 1993 

area altitude distributions (the numbers previously 

given in this abstract use the 1993 area altitude 

distribution). Net balance was about 25 percent 

less negative using the 1993 area altitude distribution than the 1967 distribution. 

Annual average air temperature was 

0.9 degree Celsius warmer than that recorded with 

the analog sensor used since 1966. Total precipitation catch for the year was 0.78 meter, 0.8 standard deviations below normal. The annual average 

wind speed was 3.5 meters per second in the first 

year of measuring wind speed. Annual runoff 

averaged 1.50 meters over the basin, 1.0 standard 

deviation below the long-term average. 

Glacier-surface altitude and ice-motion 

changes measured at three index sites document 

seasonal ice-speed and glacier-thickness changes. 

Both showed a continuation of a slowing and thinning trend present in the 1990s.

The glacier terminus and lower ablation area 

were defined for 1996 with a handheld Global 

Positioning System survey of 126 locations 

spread out over about 4 kilometers on the lower 

glacier margin. From 1949 to 1996, the terminus 

retreated about 1,650 meters for an average retreat 

rate of 35 meters per year.

INTRODUCTION

The U.S. Geological Survey (USGS) operates a 

long-term program to monitor mass balance, climate, 

glacier geometry, ice motion, and runoff to understand 

glacier-related hydrologic processes and to improve 

the quantitative estimates of water resources, glacierrelated hazards, and the consequences of global 

change (Fountain and others, 1997). The approach has 

been to establish long-term mass-balance monitoring 

programs at three widely spaced glaciers in the United 

States that clearly sample different climate-glacierrunoff regimes. Gulkana Glacier is one of these. The 

others are Wolverine Glacier in south-central Alaska 

and South Cascade Glacier in Washington. This report 

contains the meteorological, area altitude distribution, 

mass-balance, surface-altitude, ice-motion, terminusposition, and runoff measurements made at Gulkana 

Glacier for the 1996 balance year (see “Measurement 

System and Terminology” section). The data are 

reported in order of their causal hierarchy as shown in 

figure 1. 

Measurements began on Gulkana Glacier during 

the early 1960s with the University of Alaska Gulkana 

Glacier Project (Péwé and Reger, 1983). For 
2 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

several years this project measured the energy budget, 

mass balance, meteorology, foliation, flow, and glacier-bottom topography at Gulkana Glacier. In 1966, a 

continuing series of measurements was begun by the 

USGS as part of the United States contribution to the 

International Hydrologic Decade study of mass balances on selected glaciers. Detailed results from 1966 

and 1967 are reported by Meier and others (1971) and 

Tangborn and others (1977), respectively. Measured 

winter snow balance and annual balance from 

1966–77 are reported by Meier and others (1980). 

Balance studies were relatively intensive until the 

mid-1970s, after which spatial sampling was reduced 

to three sites used as indexes for mass balance. Measurements at the three remaining sites were expanded 

to include ice-motion and surface-altitude observations (for determining glacier-volume change). Since 

1966, part of the Gulkana balance data set has been 

published by the World Glacier Monitoring Service 

(http://www.geo.unizh.ch/wgms/) in both a 5-year 

“Fluctuations of Glaciers” series (Kasser, 1967; 

Muller, 1977; Haeberli, 1985; Haeberli and Müller, 

1988; Haeberli and Hoelzle, 1993; Haeberli and others, 1998) and a 2-year “Glacier Mass Balance Bulletin” series (Haeberli and Herren, 1991; Haeberli and 

others, 1993, 1994, 1996, and 1999) 

and by Mayo and Trabant (1986). 

Data for 1992, 1993, 1994, and 

1995, similar to those presented 

here, were published by March and 

Trabant (1996, 1997) and March 

(1998, 2000). Select data, maps, and 

photographs from Gulkana Glacier 

and a bibliography are available on 

the Internet at 

http://ak.water.usgs.gov/glaciology/

The Gulkana record (31 years of 

balance data, 30 years of meteorology data) has just reached the 

30-year length-of-record criterion 

(generally considered necessary to 

provide reasonable statistics) used 

in the selection of stations for international exchange through the 

Global Telecommunications Service 

for global climate monitoring (Karl 

and others, 1989). Interpretations of 

regional climate-glacier relations 

using the Gulkana data include 

papers by Fahl (1973), Letréguilly 

and Reynaud (1989), Walters and Meier (1989), 

Dowdeswell and others (1997), Hodge and others 

(1998), and Trabant and others (1998).

Description of Gulkana Glacier Basin and Its 

Climate

Gulkana Glacier (figs. 2 and 3) (lat 63°16' N., 

long 145°25' W.) is a compound valley glacier on the 

south flank of the eastern Alaska Range. The accumulation area consists of four adjacent cirques with east, 

south, and west exposures that reach as high as 

2,470 m. The ablation area flows south-southwestward, and the terminus is lightly covered with rock 

debris (fig. 3) at 1,160 m. Slightly contorted moraines 

near the terminus (fig. 3) suggest that Gulkana Glacier 

has possibly surged in the past, but no flow instabilities have been detected since scientific investigation 

began in the early 1960s. 

The mean equilibrium line altitude (ELA) since 

1966 is near 1,770 m, which is consistent with a continental mountain climate. The mean annual air temperature near the ELA is about -6 °C, lapsed from the 

weather station using the wet adiabatic rate of -6.6 °C 

per 1,000 m. The mean annual air temperature at the 

-

Figure 1. Diagram showing the cause and effect relationships for the data presented in this 

report (modified from Meier, 1965, and Fountain and others, 1997).
Introduction 3

weather station at 1,480 m is about -4 °C, and daily 

mean temperatures range from a low of -35 °C to a 

high of 15 °C. The average annual precipitation-gage 

catch is about 1 m. Over the entire basin, the average 

runoff for water years 1967–78 and 1990–96 is 

1.91 m.

In 1967, the 31.5-km2 basin was about 70 percent 

covered by perennial snow and ice. Gulkana Glacier is 

the largest glacier in the basin, covering 19.3 km2 in 

1967. The basin also contains Pegmatite Glacier 

(fig. 2), three small unnamed glaciers, and perennial 

snow and ice patches that had a total area of 2.9 km2 in 

1967. 

Gulkana Glacier has been in general recession 

since the culmination of its last advance around 1900 

(Péwé and Reger, 1983). The total recession since then 

has been about 3 km. 

Measurement System and Terminology 

Seasonal monitoring on Gulkana Glacier consists 

of three basic measurements: surface mass balance, 

surface altitude, and ice motion. These measurements 

are made repeatedly at three fixed locations on Gulkana Glacier, referred to as the “index sites” or “measurement sites” (labeled A, B, and D in figs. 2 and 3). 

Balance-motion stakes maintained near each index site 

support the long-term data collection. 

The combined mass-balance system of measurement and reporting terminology (Mayo and others, 

1972) is used in this report, with the addition of internal accumulation (Trabant and Mayo, 1985) and internal ablation (March and Trabant, 1997). The combined 

mass-balance system is based on balance measurements relative to time-transgressive stratigraphic horizons (summer surfaces) and evaluation of adjustment 

quantities for determining both net (stratigraphic) and 

annual (fixed-date) balances. The balance year used 

for the net mass balance is the interval between the 

minimum glacier-wide mass balance in 1 year and the 

minimum glacier-wide mass balance the following 

year. Thus, the net balance has a beginning and ending 

date. To calculate a true net balance it is necessary to 

run a simple balance model (see section on “Balance 

STATION

WEATHER

145° 25'

Gulkana

PHELAN CREEK STREAM GAGE

63° 15'

145° 30'

ALASKA

Glacier

A

63° 18'

145° 30'

W est Branch

LAND- AND GLACIER-SURFACE 

CONTOURS. INTERVAL 100 METERS.

2 KILOMETERS

GLACIER BOUNDARY

STREAM GAGING STATION

MEASUREMENT STAKE

0

0

BASIN BOUNDARY

1

1 MILE

63° 15'

EXPLANATION

WEATHER STATION

SNOW PIT

B D

RANGE

ALASKA

Base map, including glacier contours and boundary, from Tangborn and others, 1977.

Figure 2. Gulkana Glacier and vicinity (NAD 27, NGVD of 1929).
4 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

at Specific Sites”) to extrapolate from the nearest measurement to the time and value of the glacier-averaged 

net balance. In most years, the balance minimum 

occurs at different times on different parts of the glacier (earlier high on the glacier and later low on the 

glacier). Thus, an area integration of the local balance 

minimums yields a pseudo area-averaged balance that 

is not clearly defined with regard to time and does not 

represent the actual balance on the glacier at any 

moment.

The hydrologic year, which is the period used for 

the annual (fixed-date) mass balance, meteorological 

data, and runoff, is the interval between October 1 and 

the end of the following September. It is designated by 

the calendar year in which it ends. The hydrologic year 

coincides with the USGS “water year.” For simplicity 

“this year” or the “current year” are used in this report 

to indicate the time period reported in this report, 

which may be either the balance year, hydrologic year, 

or some similar period depending on the data being 

discussed. The temporal relations of the quantities 

defined and used for analyzing the index-site and 

glacier-averaged 1996 mass balances are illustrated in 

figures 4 and 5.

All balance values are reported in meters water 

equivalent. Density values are reported in kilograms 

per liter and thus are numerically equivalent to the 

unitless relative density (the decimal fraction of the 

density of water). The density of water is 1,000 kg/m3

or 1 kg/L, and that of glacier ice is assumed to be 

900 kg/m3.

Figure 3. Composite vertical photograph of Gulkana Glacier and its basin showing index-measurement sites, streamgaging station, weather station, and basin boundary, July 11, 1993 (photographs Gulkana Gl 1 No. 5 and Gulkana Gl 2 

No. 4 by AeroMap U.S., Inc.). A, B, and D are measurement sites for mass balance, ice motion, and surface altitude. 

Dash-dot-dot-dash line indicates basin boundary.
Introduction 5

Altitude is reported in meters above NGVD of 

1929. Horizontal locations are defined in a local sealevel-scale network with the positive Y-axis approximately true north; these coordinates may be converted 

to Universal Transverse Mercator (UTM) zone 6 coordinates (NAD 83) by:

UTM Easting = XL + 575,000 m, and (1)

UTM Northing = YL + 7,011,000 m, (2)

where is the mean horizontal scale factor between 

the UTM plane and sea level and XL and YL are local 

coordinates, in meters. 

The scale factor, k, at a point is a variable defined 

by:

, (3)

where E is the UTM Easting of the point and the trigonometric function is evaluated in grad.

The mean scale factor used in equations 1 and 2 is 

the mean value of the nonlinear distribution of scale 

factors between the local origin and an observation 

point. E is approximated by the sum of the UTM Easting of the local origin (575,000 m) and XL.

 . (4)

Equation 5 is accurate within about 0.1 part per million of equations from U.S. Departments of the Army 

and the Air Force (1951, specifically see page 219 and 

appendixes IV and V) and, hence, yields results accurate at the centimeter level.

k

k

k

k 0.9996

100 500 000 , – E

100 000 , + ------------------------------ ⎝ ⎠ ⎛ ⎞ sin

= -----------------------------------------------------------

k 1

XL

----- k Ed

( ) 575 000 ,

575 000 , XL ( ) +

∫ =

- 4.0

- 3.5

- 3.0

- 2.5

- 2.0

- 1.5

- 1.0

- 0.5

0.0

0.5

1.0

1.5

2.0

MASS BALANCE, IN METERS WATER EQUIVALENT

b n

Site A , ~1,370 m.

Site B , ~1,690 m.

Site D , ~1,840 m.

SNOW

OLD FIRN OR ICE

b m(s)

b w (s) b o (s)

LAT E SNOW

LAT E SNOW

b n

b n

b w (s)

b m(s)

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 

b m(s) b w (s)

Figure 4. Time distribution of index-site mass balances for Gulkana Glacier, 1996 hydrologic year. Solid circles are measured

values; open circles are estimated values. Seasonal maximum balances occurred during late May. b0(s), initial snow balance at 

site; bm(s), measured winter snow balance at site; bn, net balance at site; bw(s), maximum winter snow balance at site. Site 

altitudes are approximate long-term averages rounded to the nearest 10 meters.

The mean scale factor is estimated using Simpson’s rule (Cheney and Kincaid, 1980):

k . (5) 0.9996

6 ---------------- 1

100 500 000 575 000 , – ( ) ,

100 000 , + ---------------------------------------------------- ⎝ ⎠ ⎛ ⎞ sin

--------------------------------------------------------------------------------- 4

100

500 000 575 000 – ( ) , 1

2

--XL , –

100 000 , + ---------------------------------------------------------------------

⎝ ⎠ ⎜ ⎟

⎛ ⎞

sin

-------------------------------------------------------------------------------------------------- 1

100

500 000 575 000 – ( ) , XL , –

100 000 , + ----------------------------------------- ⎝ ⎠ ⎜ ⎟ ⎛ ⎞

sin

+ + -----------------------------------------------------------------------------------------------

⎝ ⎠ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎛ ⎞

=
6 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

DATA COLLECTION 

The temporal distribution of the data collected for 

the 1996 balance year is shown in table 1. Air temperature, precipitation catch, wind speed, and Phelan 

Creek stage data are recorded continuously. The stage 

data are not recorded after Phelan Creek freezes in the 

early fall, and runoff is estimated for most of the fall, 

winter, and spring. Phelan Creek discharge measurements to calibrate the stage are made during onsite 

visits several times during open water and several 

times during the ice-affected period. The meteorological and runoff data sets reported here are truncated to 

the hydrologic year, October 1 to September 30. 

The mass-balance, glacier-surface altitude, and 

ice-motion data were collected during four onsite 

visits between late September 1995 and mid-April 

1997 (table 1). Generally the visits were timed to 

define the mass-balance maximums and minimums, 

usually during spring (March/April/May) and latesummer/early-fall (September/October), respectively. 

In addition to measuring the near-maximum balance, 

observations during the spring add redundancy to the 

previous fall measurements of the height of the summer surface on the balance-motion stakes and, hence, 

support a regular assessment of errors in balance calculations made on the basis of stake measurements. 

Terminus position is measured during one onsite visit 

near the end of the summer.

METEOROLOGY

Air Temperature

Air temperature is recorded by an analog recorder 

at 1,480 m on the eastern ice-cored moraine of Gulkana Glacier (weather station, figs. 2 and 3; see 

Kennedy and others, 1997). The daily mean 

temperatures reported (fig. 6, table 2) have an accuracy of about ±1.0 °C (Kennedy and others, 1997). 

Following the National Climatic Data Center (1996) 

convention, monthly mean temperatures are calculated 

for months with nine or fewer missing daily values.

- 0.6

- 0.4

- 0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

GLACIER-AVERAGED MASS BALANCE, 

IN METERS WATER EQUIVALENT

b (s) o

bm (s) bw (s)

bn ba

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP 

Figure 5. Time distribution of glacier-averaged mass balance of Gulkana Glacier, 1996 hydrologic year (using 1993 area 

altitude distribution). Solid circles are measured values; open circles are estimated values. Symbols with a bar over them 

indicate the average value over the whole glacier. The initial balance, b0(s), is the change in balance between the balance 

minimum that defines the beginning of the net balance year and the beginning of the hydrologic year (October 1). The 

measured winter snow balance, bm(s), is the snow above the previous summer surface measured near the time of the 

maximum winter snow balance, bw(s). bn, net balance; ba, annual balance.
Meteorology 7

Table 1. Summary of data collection in Gulkana Glacier Basin for the 1996 balance year analysis 

[ , continuous record; , estimated record; •, occasional/discrete measurement]

Data Approximate 1996 hydrologic year 1997 hydrologic year

collection sites altitude1 Measurement 1995 calendar year 1996 calendar year 1997 calendar year

(fig. 1 and 2) (meters) Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr.

Phelan Creek Stage

gaging

station

1,140 Discharge

Mass balance

Site A 1,370 Surface motion

Surface altitude

Weather Air temperature

station 1,480 Precipitation catch

Wind speed

Mass balance

Site B 1,690 Surface motion

Surface altitude

Mass balance

Site D 1,840 Surface motion

Surface altitude

Firn interface 

temperature

Terminus position determined

1 Altitudes are approximate long-term averages rounded to the nearest 10 meters.

Gulkana Glacier - 1480 Meter Weather Station

Period of Record: 1968 to 1996

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

DAILY MEAN AIR TEMPERATURE, IN DEGREES CELSIUS

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

1996

Record high

Average

Record low

Figure 6. Daily mean air temperature recorded at 1,480-meter weather station, Gulkana Glacier Basin, 1996 hydrologic year. Also 

shown are record high, average, and record low daily mean temperatures since 1968. 
8 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Starting this year, a digital temperature sensor also 

was used (table 3). It is located adjacent to the analog 

sensor in the same shelter. It has an accuracy of 

±0.1 °C and time constant of 10 seconds in air, considerably faster than the analog sensor. Fifteen-minute 

average temperatures are recorded by the digital sensor from which the daily average is determined.

The annual average temperature for 1996 with the 

analog sensor was -5.0 °C, 0.9 standard deviation 

below the long-term average of -4.1 °C (1968–91, 

1993–95). The winter average temperature from 

September 1, 1995, to May 15, 1996, was -8.3 °C, 

about 0.2 standard deviation below the long-term average. The summer average temperature from May 16 to 

August 30, 1996, was 4.0 °C, about 1.0 standard deviation below the long-term average. (The winter and 

summer average temperature periods correspond to the 

average maximum and minimum glacier-averaged balance periods to within about one-half month.)

The annual average temperature for 1996 with the 

digital sensor was -4.1 °C, 0.9 °C warmer than the analog sensor. This average difference is within the accuracy of the analog sensor. Some difference between 

sensors was expected due to the large difference in 

their time constants. Plans are to collect several years 

of overlapping data for further analysis.

Precipitation Catch

Precipitation catch (fig. 7, table 4) is recorded at 

the weather station (figs. 2 and 3) by an analog 

recorder connected to a storage-type precipitation gage 

with a modified Nipher shield (see Kennedy and others, 1997). Previously, precipitation catch data have 

been processed with a temperature and water-concentration dependent density correction. However, new 

analysis, not possible at the beginning of the USGS 

Gulkana Glacier monitoring program, shows that the 

density correction is incomplete and actually increases 

Table 2. Daily, monthly, and annual average air temperatures from analog sensor recorded at 1,480-meter weather station, Gulkana 

Glacier Basin, 1996 hydrologic year

[Values in degrees Celsius]

1995 1996

Day Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Annual

1 - 0.9 - 2.8 -24.7 - 8.0 -15.1 - 4.3 -17.0 - 5.6 5.4 3.4 3.8 3.5

2 - 1.1 - 7.6 -28.7 -11.4 -19.3 - 5.8 -19.3 - 5.2 6.6 5.4 1.7 3.7

3 - 1.5 -10.4 -30.6 - 9.5 -18.8 - 6.0 -14.5 - 2.9 1.8 8.0 1.4 5.2

4 - 2.2 -12.9 -28.8 -10.4 -17.8 - 9.7 - 4.7 - 2.6 - 0.6 8.3 3.3 5.8

5 - 4.6 -14.6 -29.3 -11.8 - 7.5 -12.2 - 4.7 - 1.5 0.8 6.1 1.9 4.5

6 - 3.1 -16.6 -24.8 -16.9 - 5.4 -14.8 - 5.8 - 0.1 5.5 7.3 1.4 5.0

7 - 1.5 -13.0 -20.2 -23.1 -14.4 -16.8 - 8.8 0.0 5.4 7.4 3.3 4.3

8 - 1.0 - 9.7 -17.0 -19.8 -15.8 -13.4 -10.0 - 3.1 0.2 7.4 4.1 4.9

9 - 1.7 -13.6 -16.4 -20.8 -13.0 -13.0 - 7.9 0.2 2.8 5.2 1.7 1.5

10 - 4.1 -14.5 -15.5 -22.1 - 5.2 -12.1 - 4.0 3.2 0.9 5.0 0.4 1.7

11 - 3.1 -16.6 -10.4 -26.0 - 5.1 -11.8 - 4.5 3.1 0.8 5.1 3.2 0.2

12 - 6.6 -13.8 - 8.1 -23.1 - 7.3 - 9.4 - 4.9 3.7 3.0 3.4 3.2 3.3

13 - 8.3 -14.4 -14.5 -19.1 - 8.8 - 8.1 - 4.9 3.8 3.3 2.2 4.3 3.7

14 -10.4 -14.1 -14.6 -18.6 - 6.4 - 7.8 - 2.8 - 6.7 3.9 1.8 4.5 0.2

15 - 7.2 -11.4 -11.5 -17.1 - 8.4 - 9.7 - 0.2 - 3.6 5.5 4.1 5.6 1.3

16 - 6.2 - 7.5 - 9.3 -16.6 -10.7 -10.0 - 1.3 - 0.9 7.5 7.1 5.7 1.5

17 - 7.1 - 5.8 - 9.4 -17.3 -14.2 -10.4 0.8 - 1.0 8.8 6.9 4.6 3.2

18 - 7.3 - 8.2 - 8.2 -18.7 -13.5 - 8.8 1.7 - 1.7 9.1 8.3 4.7 1.0

19 - 2.4 - 6.9 - 6.1 -17.8 -22.7 -16.5 2.5 - 3.1 10.0 9.3 5.3 - 1.9

20 - 5.2 - 8.4 - 7.2 -15.7 -27.2 -10.0 - 1.4 - 2.8 9.2 9.0 5.2 - 2.8

21 - 5.1 - 7.3 - 6.9 -15.3 -25.4 - 9.8 - 2.9 - 0.1 8.4 6.6 2.4 - 3.7

22 - 4.0 - 7.7 - 6.1 -14.2 -22.7 - 6.8 - 2.1 1.3 9.5 5.0 2.3 - 5.3

23 - 5.4 - 7.2 - 3.7 -16.1 -26.1 - 6.1 - 0.5 3.8 10.5 6.9 4.2 - 7.1

24 - 4.2 - 8.5 - 6.2 -21.4 -18.9 - 6.6 - 4.4 1.1 8.1 8.5 3.7 - 6.7

25 - 3.8 -11.7 - 3.9 -20.1 - 8.8 - 7.6 - 1.4 0.8 3.2 6.4 1.7 - 1.6

26 - 7.7 -14.2 - 4.5 -20.1 - 8.8 - 6.6 - 1.5 1.8 2.9 5.6 - 0.9 - 5.7

27 -10.3 -13.1 - 4.6 -20.1 - 7.5 - 8.9 - 4.1 - 0.7 2.4 4.3 - 3.0 - 5.9

28 - 9.1 -12.7 - 7.6 -17.4 - 3.3 - 6.6 - 4.4 0.3 1.2 9.3 0.2 - 6.0

29 - 7.1 -15.2 - 7.7 -10.6 - 2.2 - 7.7 - 3.2 4.4 2.0 9.1 3.6 - 7.4

30 - 1.7 -22.9 - 7.4 - 7.8 -11.7 - 2.3 6.6 3.0 3.2 2.7 - 7.8

31 1.2 - 7.6 -10.8 -13.6 5.2 4.2 0.4

Average - 4.6 -11.4 -13.0 -16.7 -13.1 - 9.8 - 4.6 - 0.1 4.7 6.1 2.8 - 0.2 - 5.0

Departure from normal 1.2 - 1.1 - 1.1 - 3.5 - 1.3 0.7 0.3 - 1.4 - 0.2 - 0.4 - 2.0 - 0.8 - 0.9

Standardized value 0.6 - 0.4 - 0.4 - 0.8 - 0.4 0.3 0.1 - 1.0 - 0.1 - 0.4 - 1.2 - 0.5 - 0.9
Meteorology 9

the measurement error rather than reducing it. Hence, 

it was not used in this year’s data processing. Comparison of density-corrected data to non-density-corrected 

data for previous years shows monthly and annual differences of several percent. These differences are 

judged to be minor compared to other errors. Daily 

value differences can be much greater, with 

precipitation occasionally shifted from 1 day to an 

adjacent day. 

The precipitation-catch record for the 1996 hydrologic year shows evidence of fluid loss through 

April 19, 1996. This could have been caused either by 

a fluid leak in the storage tank or by evaporation, 

which is normally prevented by an oil film on the surface of the stored antifreeze-water solution. Because 

the functioning of the precipitation gage returned to 

normal after replacing the oil film in the storage tank 

on April 20, 1996, it is concluded that the oil film was 

inadequate prior to that. As a result, the record up 

through April 19 was processed separately to compensate for the evaporation as best as possible. This 

process is complicated because even when the gage is 

working normally, the fluid height in the gage frequently drops by small amounts due to temperaturedriven gage and fluid expansion/contraction and measurement error. Hence, all negative gage-height 

changes can not be thrown out of the data set. Instead, 

the quantity of negative gage-height changes was 

reduced to a level comparable to years when the gage 

was functioning normally. 

Despite the problems, processing the precipitation-catch record to compensate for evaporation is 

considered better than using the precipitation record 

from the nearest National Weather Service station, 

Paxson (station 50709704, located at 823 m, about 

20 km south of the Gulkana weather station). On the 

basis of data from 1975–84 and 1986–92, the Paxson 

gage catches only about one-half as much precipitation 

annually, and the Pearson (conventional) correlation 

coefficient between Gulkana and Paxson daily precipitation values is only 0.62. 

Table 3. Daily, monthly, and annual average air temperatures from digital sensor recorded at 1,480-meter weather station, Gulkana 

Glacier Basin, 1996 hydrologic year

[Values in degrees Celsius; -, daily value missing; M appended to value, insufficient or partial data, up to 9 days missing in average]

1995 1996

Day Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Annual

1 — - 1.5 -24.0 — -14.4 - 3.5 -16.2 - 4.6 6.1 5.2 4.7 2.2

2 — - 6.7 -27.7 -10.4 -18.7 - 5.5 -18.9 - 4.8 7.7 7.0 2.8 4.4

3 - 0.3 - 9.4 -30.1 - 8.2 -18.2 - 6.0 -13.7 - 1.4 3.2 9.0 3.1 5.9

4 - 1.5 -12.2 -27.5 - 9.6 — - 8.7 - 3.6 - 1.7 1.1 8.2 4.7 6.6

5 - 3.7 -13.8 -28.8 -10.7 — -11.4 - 3.7 - 0.5 1.5 6.6 2.4 4.7

6 - 2.0 -16.4 -23.9 -16.3 - 4.7 -14.4 — 1.1 6.2 8.5 2.9 4.8

7 - 0.7 -12.0 -18.7 -21.8 -13.5 -16.5 - 8.4 0.7 6.7 9.7 4.9 4.6

8 - 1.0 - 9.0 -16.3 -18.9 -15.2 -12.2 - 9.6 - 1.9 1.6 8.1 5.4 4.9

9 - 1.6 -12.9 -15.5 -20.3 -11.4 -12.3 - 7.2 0.8 3.6 6.2 2.6 2.2

10 - 3.4 -13.4 -14.7 -21.2 - 3.8 -11.8 - 4.0 3.9 2.2 6.1 1.7 2.0

11 - 2.4 -15.9 - 9.4 -25.5 - 4.4 -11.3 - 3.8 3.9 2.1 5.9 4.6 —

12 - 5.8 -12.7 - 7.3 -22.3 - 6.7 - 8.6 - 4.4 4.9 3.9 4.5 4.6 —

13 - 7.1 -13.4 -13.6 -18.5 - 7.4 - 7.3 - 4.3 4.9 3.9 3.0 4.4 4.3

14 - 9.9 -12.9 -13.6 -17.8 - 6.1 - 7.0 - 2.0 - 1.2 4.9 2.8 5.5 1.1

15 - 6.1 -10.8 - 9.9 -16.3 - 7.6 - 8.7 - 0.1 - 2.2 6.6 5.4 7.0 2.0

16 - 5.7 - 6.6 - 8.3 -15.5 -10.0 - 9.3 - 1.0 0.4 8.7 8.3 6.7 1.9

17 - 6.0 - 4.6 - 8.4 -16.7 -13.6 -10.2 1.9 0.1 9.7 7.5 5.7 3.3

18 - 7.1 - 7.8 - 6.7 -17.7 -12.3 - 8.7 2.6 - 0.3 9.6 9.2 6.0 2.0

19 - 1.5 - 6.0 - 5.2 -16.9 -21.9 -15.3 — - 2.0 10.6 10.2 7.0 - 1.4

20 - 4.7 - 7.9 - 6.7 -14.4 -26.9 - 9.7 - 0.6 - 1.1 9.9 9.9 6.0 - 2.2

21 - 4.0 - 6.4 - 6.0 -14.2 -25.3 -10.1 - 1.3 1.0 9.2 7.4 3.4 - 2.6

22 - 2.8 - 7.1 - 5.0 -13.2 -21.6 - 7.1 - 0.9 2.9 10.4 6.0 3.8 - 4.7

23 - 4.8 - 6.3 - 3.0 -15.9 -26.1 - 5.9 0.4 4.0 11.0 8.1 5.1 - 6.6

24 - 3.1 - 7.4 - 4.8 -20.9 -17.1 - 5.9 - 3.2 2.5 8.8 10.0 4.7 - 5.9

25 - 2.9 -10.7 - 2.8 -19.9 - 7.8 - 7.8 - 0.6 1.5 4.9 7.3 2.8 - 0.4

26 - 6.3 -13.1 - 3.7 -19.4 - 8.2 - 6.0 - 0.3 0.9 3.9 6.9 0.7 - 5.0

27 - 9.0 -12.6 - 4.0 -19.5 - 6.4 - 7.9 - 2.7 0.6 4.1 5.9 - 1.9 - 5.6

28 - 8.4 -11.6 - 6.2 -16.5 - 2.6 - 6.5 - 3.2 1.3 2.2 11.2 2.3 - 6.7

29 - 5.6 -13.7 - 6.3 - 9.5 - 1.6 - 6.3 - 1.9 5.5 2.1 9.8 4.8 - 7.7

30 0.0 -22.2 - 6.2 - 6.7 -10.6 - 1.2 7.5 4.1 4.2 3.5 - 6.6

31 — - 7.0 - 9.9 -12.9 5.9 5.4 —

Average - 4.2M -10.6 -12.0 -16.2M -12.4M - 9.2 - 4.0M 1.1 5.7 7.2 4.1M 0.1M - 4.1M
10 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Daily precipitation catch (fig. 7, table 4) has an 

estimated accuracy of ±0.001 m normally, and prior to 

April 20, 1996, the estimated accuracy was ±0.003 m. 

Cumulative precipitation catch for the month is estimated to have an accuracy of ±0.002 m (Mayo and 

others, 1992; Kennedy, 1995). 

The complex relation between precipitation catch 

and true basin precipitation has not been thoroughly 

analyzed at Gulkana. It is generally well known that 

catch efficiencies are not constant but vary with wind 

speed, direction, and the nature of the precipitation. At 

Wolverine Glacier, which has a windier environment 

than Gulkana, the gage-catch efficiency was found to 

be about 0.31 relative to true basin precipitation for a 

10-year period (Mayo and others, 1992). From 

April 27, 1967, to September 30, 1967, the catch efficiency of the Gulkana gage was calculated at 0.52 

(Tangborn and others, 1977), although the wind shield 

has since been modified to what is believed to be a 

more efficient design. For hydrologic years 1968–78 

and 1990–91, the average catch efficiency for the Gulkana Basin was 0.57. Despite the low catch efficiencies, precipitation catch is useful as an indicator of true 

basin precipitation. 

Wind Speed

The 1996 hydrologic year is the first full year of 

wind-speed data collection from the 1,480-m weather 

station (fig. 8, table 5). The sensor is a Taylor Scientific Engineering WS-3 rotor anemometer designed for 

a very windy, rugged mountain environment and 

installed on a 3-m mast. The threshold wind speed is 

1.34 m/s, and it has a time constant of 7 to 8 seconds 

for a step increase in wind speed and 19 to 20 seconds 

for a step decrease. The sensor’s accuracy is about 

±0.5 m/s. Fifteen-minute average wind speeds are 

recorded. 

Annual average wind speed for 1996 was 3.5 m/s. 

Maximum daily average wind speed for the year was 

15.0 m/s recorded on November 4, 1995, and March 9, 

1996. Maximum 15-minute average wind speed was 

23.5 m/s on February 19, 1996. Wind speeds greater 

than 5 to 8 m/s, the threshold for blowing snow (Barry, 

1989), occur 15 to 20 percent of the time. Wind 

entrainment and redeposition of snow may be an 

important mass-balance process at Gulkana Glacier. 

Average monthly wind speed is shown in figure 9. 

Gulkana Glacier - 1480 Meter Weather Station

Period of Record: 1968 to 1996

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

DAILY PRECIPITATION CATCH, IN MILLIMETERS 

Record high

Average

1996

Figure 7. Daily precipitation catch recorded at 1,480-meter weather station, Gulkana Glacier Basin, 1996 hydrologic year. Also

shown are record high and average daily precipitation catch since 1968. 
Meteorology 11

Table 4. Daily and monthly precipitation catch recorded at 1,480-meter weather station, Gulkana Glacier Basin, 1996 hydrologic 

year 

[Values in millimeters]

1995 1996

Day Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Annual

1 020100000250

2 0 0 0 0 0 0 0 0 0 1 16 3

3 000000130521

4 000040900000

5 0 0 0 0 19 0 0 1 0 5 13 0

6 000020032410

7 001000000040

8 004100004100

9 0 0 0 0 1 0 0 0 4 0 21 0

10 0 0 1 0 10 0 0 2 2 7 43 0

11 0 0 10 0 0 0 0 0 0 0 6 7

12 0 0 0 0 0 0 0 1 4 0 2 0

13 0 0 0 0 0 9 0 0 6 18 8 1

14 0 2 0 0 0 5 0 0 0 18 1 0

15 1 0 10 0 0 2 0 0 4 2 2 0

16 0 6 7 0 0 5 0 0 1 1 8 1

17 0 2 0 0 0 0 0 0 0 4 0 1

18 0 0 1 0 0 0 0 1 2 1 0 1

19 3 0 2 0 0 0 0 7 2 0 0 0

20 0 0 1 0 0 0 11 6 0 0 0 0

21 4 0 0 0 0 0 0 4 0 0 0 8

22 0 0 0 0 0 0 0 1 1 8 4 1

23 5 0 0 0 0 0 0 1 0 5 6 4

24 2 0 0 0 7 0 0 1 0 2 5 1

25 0 0 3 0 17 0 4 3 6 2 6 5

26 0 0 0 0 4 0 1 11 0 1 9 11

27 0 0 0 0 1 0 0 6 2 1 3 1

28 0 0 0 0 1 0 0 2 2 11 4 3

29 1 0 0 6 0 0 2 5 21 0 19 0

30 5 0 16 8 0 1 0 2 45 32 0

31 2 6 0 0 0 4 10

Total 23 12 62 16 66 21 29 58 65 148 230 49 779

Departure from normal -86 -49 - 6 -42 12 -40 -11 11 -19 34 80 -89 -204

Standardized value - 1.4 - 1.1 - 0.1 - 1.3 0.4 - 1.0 - 0.4 0.5 - 0.4 0.4 0.8 - 1.0 - 0.8

Figure 8. Daily average wind speed recorded at 1,480-meter weather station in Gulkana Glacier Basin, 1996 hydrologic 

year. Smooth is an inverse distance weighted smooth of the data using an 11-day window.

0

2

4

6

8

10

12

14

16

18

20

DAILY AVERAGE WIND SPEED, 

IN METERS PER SECOND

1996

Smooth

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
12 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Table 5. Daily mean wind speed from the Gulkana Glacier Basin, 1996 hydrologic year 

[Values in meters per second; M appended to value, insufficient or partial data, up to 9 days missing in average; -, daily value missing]

1995 1996

Day Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Annual

1 — 2.3 8.6 — 1.2 3.7 8.6 7.4 5.7 5.7 3.7 5.5

2 3.7 0.5 12.0 1.3 0.8 1.5 3.7 3.7 3.1 6.3 4.0 6.8

3 1.4 6.3 2.7 1.3 3.7 1.4 1.5 3.1 8.8 7.4 4.3 4.6

4 1.0 15.0 4.6 0.2 — 12.0 2.0 7.1 7.1 2.8 4.3 5.9

5 4.8 10.0 3.4 6.6 — 12.0 4.0 4.3 4.8 2.5 3.7 2.1

6 2.1 1.6 0.9 14.0 7.4 1.9 — 2.6 4.0 3.7 8.8 3.0

7 0.8 2.7 0.7 9.1 6.6 1.3 2.7 4.6 4.6 5.4 8.6 3.6

8 0.6 7.7 1.8 1.3 6.6 2.8 1.7 8.3 3.4 1.9 2.8 2.8

9 1.3 4.8 2.4 1.5 5.7 15.0 1.7 2.7 2.4 2.2 3.4 3.3

10 0.7 6.0 1.1 4.8 7.7 4.8 1.1 2.7 1.4 4.0 2.4 2.4

11 2.0 5.7 0.7 9.4 8.6 0.9 1.5 6.8 4.0 3.7 1.6 —

12 3.1 1.7 1.5 1.4 4.3 1.5 2.1 5.4 7.1 2.5 1.9 —

13 1.1 1.3 0.7 0.7 2.2 0.5 2.1 3.7 4.3 3.7 1.6 4.6

14 0.6 1.1 0.8 1.0 0.9 1.3 1.7 12.0 2.0 2.1 2.4 5.4

15 0.3 2.0 0.3 0.9 1.3 5.1 0.4 5.1 5.7 5.1 2.8 1.0

16 2.2 1.9 0.3 0.8 5.7 4.0 1.5 1.3 4.3 4.0 4.0 3.1

17 1.9 1.9 1.0 1.1 1.5 2.1 2.0 0.9 4.0 4.3 7.1 2.6

18 1.9 0.9 2.0 1.1 1.6 4.0 1.4 4.0 4.0 4.8 6.6 3.1

19 3.4 2.6 2.7 1.2 13.0 10.0 5.7 5.7 3.1 4.8 5.1 2.9

20 0.5 1.5 3.1 1.5 4.8 1.2 1.7 4.8 3.1 4.0 1.4 2.9

21 1.7 2.1 2.6 2.1 1.1 1.2 2.6 3.1 4.0 3.1 1.7 4.1

22 2.4 0.7 2.5 1.3 12.0 2.0 4.0 2.7 8.0 2.3 1.8 3.2

23 0.5 3.7 3.1 2.2 4.8 1.3 3.1 3.7 3.4 2.8 1.5 2.5

24 5.4 8.0 2.3 0.9 0.9 1.1 4.3 3.4 6.0 2.5 2.1 2.9

25 1.5 7.4 2.3 1.0 3.1 1.6 2.8 2.7 5.7 2.4 8.0 9.7

26 1.3 4.0 3.4 1.5 3.7 0.8 2.4 0.2 3.4 2.8 3.7 1.9

27 1.4 2.0 2.8 1.0 1.7 8.0 4.3 1.2 2.5 2.0 9.9 0.4

28 2.5 1.6 3.7 0.9 2.4 1.0 3.7 2.7 0.8 2.5 2.5 2.1

29 3.4 9.7 1.1 0.9 2.2 6.6 6.8 2.8 2.3 4.0 4.7 2.0

30 3.4 13.0 0.0 0.6 7.1 3.7 3.1 8.3 4.0 2.0 0.5

31 2.3 0.1 1.3 6.0 5.4 1.4 —

Average 2.0M 4.3 2.4 2.4M 4.3M 4.0 2.9M 4.1 4.4 3.6 3.9M 3.4M 3.5M

Figure 9. Monthly average wind speed recorded at 1,480-meter weather station in Gulkana Glacier Basin for 

1996 hydrologic year.

0

1

2

3

4

5

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP

MO NTHLY AVERAG E WIND SPEED,

 IN METERS PER SECO ND .
Area Altitude Distribution 13

AREA ALTITUDE DISTRIBUTION

Two area altitude distributions are used in this 

report. The first is the area altitude distribution of the 

glacier and basin defined for the 1967 balance analysis 

(fig. 10) (Tangborn and others, 1977; see March, 1998, 

for tabulation of these values). These values are based 

on a 100-m contour topographic map that was defined 

from examination of the 1:63,360-scale USGS 

topographic maps, Mt. Hayes A–3 (1950) and B–3 

(1955), the original 1954 vertical mapping photography, and more recent oblique aerial photography 

(dates unknown) taken by Austin Post and Larry Mayo 

(aerial photographs are part of the USGS Ice and Climate Project Photography Collection, GeoData Center, Fairbanks, Alaska). The 1967 values have been 

used to calculate and report all glacier-averaged balances since 1967. 

The second area altitude distribution (see fig. 10 

and table 6) is based on a 30-m grid version of a higher 

resolution, but irregularly spaced, digital elevation 

model (DEM) that was photogrammetrically derived 

from 1:36,000-scale 1993 vertical photography 

(March, 2000). In 1993, snow and ice coverage in the 

basin had been reduced to 64 percent of the basin from 

70 percent in 1967. Gulkana Glacier had shrunk by 

6 percent to 18.1 km2, and other small glaciers and 

perennial snow areas had shrunk by 42 percent to 

1.7 km2

. Virtually all of the Gulkana Glacier shrinkage 

occurred below the ELA. The lack of an area reduction 

in the 1,200- to 1,300-m altitude zone could be due to 

the extensive presence of surficial debris in this zone. 

Surficial debris retards ablation when it continuously 

covers the ice surface and is thicker than a few 

centimeters.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800 1,900 2,000 2,100 2,200 2,300 2,400 2,500

ALTITUDE, IN METERS

GLACIER AREA, IN SQUARE KILOMETERS

1967

1993

SITE ASITE B

SITE D

WEATHER STATION

MEAN ELA

MEAN GLACIER ALTITUDE

Figure 10. Area altitude distribution of Gulkana Glacier in 1967 and 1993. Shown are altitudes of index sites, the weather station, the mean 

equilibrium line altitude (ELA), and mean altitude of the glacier. 
14 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

GLACIER MASS BALANCE

Balance at Specific Sites

Measured winter snow balance, maximum winter 

snow balance, net mass balance, and the annual mass 

balance are determined at each index site using largely 

traditional methods (Østrem and Stanley, 1969; 

Østrem and Brugman, 1991). The stake, pit, probing, 

coring, and meteorological data are shown in tables 7, 

8, and 9 and figure 4. 

Although mass-balance measurement locations 

commonly are referred to as “points” on a glacier, they 

are treated as small areas 25 to 75 m in radius, centered on each index site, over which measurements are 

made and the balance averaged. The area chosen is 

large enough and enough measurements are taken in 

the area so that when a quantity, such as snow depth, is 

averaged over the area, the error caused by the glaciersurface and summer-surface roughness (up to several 

meters on some glaciers) is small. Likewise, stake 

readings are made at the intersection of the average, 

“visually smoothed” glacier surface (out to 25 to 

75 m) with the stake and not just where the snow, ice, 

or firn is right at the stake. 

One departure from traditional methods is surveying of the stake and glacier-surface geometry and subsequent analysis to correct for the lean and bending, 

which commonly occur after the initial near-vertical 

installation of the stakes (March, 2000). These corrections affect the stake position for ice motion (see section on “Ice Motion”) and the height on the stake of 

the glacier surface, b ́ (table 7), which is used for some 

balance determinations. Another departure from traditional methods is the recording and combining of multiple measurements of the height of a summer surface 

on a stake to reduce balance errors (March, 2000), 

such as a fall measurement of the summer surface after 

fall snow has fallen and another measurement of the 

same summer surface in the spring near the peak 

snowpack.

Table 6. Area altitude distribution of Gulkana Glacier and Gulkana Glacier Basin by 100-meter altitude intervals as defined from a 

digital elevation model derived from July 11,1993, photography 

[Measurement site altitudes, in meters, are approximate averages for 1996 balance year. m, meters; km2, square kilometers]

Altitude Average Basin

NonglacierTotal

glacier

Gulkana

Glacier

Other

glacier

Subareas of glacier 

represented

by index sites:

interval altitude area area area area area Site A Site B Site D

(m) (m) (km2

) (km2) (km2) (km2) (km2) (km2) (km2) (km2)

1,166 - 1,200 1,181 1.31 1.23 0.08 0.08 0.08

1,200 - 1,300 1,250 1.60 1.08 0.52 0.52 0.52

1,300 - 1,400 1,350 1.86 0.93 0.93 0.93 0.93

1,400 - 1,500 1,450 2.45 1.14 1.31 1.31 1.31

1,500 - 1,600 1,550 2.43 1.24 1.20 1.13 0.07 0.27 0.86

1,600 - 1,700 1,650 3.26 1.34 1.92 1.66 0.26 1.66

1,700 - 1,800 1,750 3.67 1.09 2.57 2.00 0.58 1.14 0.86

1,800 - 1,900 1,850 4.64 1.11 3.53 2.96 0.57 2.96

1,900 - 2,000 1,950 3.90 0.89 3.01 2.79 0.22 2.79

2,000 - 2,100 2,050 2.78 0.51 2.27 2.26 0.01 2.26

2,100 - 2,200 2,150 1.74 0.38 1.36 1.36 1.36

2,200 - 2,300 2,250 1.20 0.27 0.93 0.93 0.93

2,300 - 2,400 2,350 0.24 0.05 0.19 0.19 0.19

2,400 - 2,445 2,423 0.02 0.02 0.02 0.02

Total area, in km2

 = 31.10 11.27 19.84 18.13 1.71 3.11 3.66 11.37

Altitude of index site in 1996, in m = 1,366 1,681 1,833

Average altitude of zone, in m = 1,740 1,609 1,814 1,817 1,788 1,389 1,658 1,985

Upper altitude limit of zone, in m = 1,524 1,757 2,473

Lower altitude limit of zone, in m = 1,161 1,524 1,757

Fraction of Gulkana Glacier area = 0.171 0.202 0.627

Fraction of basin area= 1.000 0.362 0.638 0.583 0.055
Glacier Mass Balance 15

Table 7. Stake, snow depth, and snow-density data for index sites A, B, and D on Gulkana Glacier, September 1995 through 

April 1997

[mm/dd/yyyy, month/day/year; stake name: the first two digits represent the year the stake was installed; letter (A, B, D) represents the site on the 

glacier (fig. 3); a number following the letter is used to differentiate multiple stakes installed at the same site in 1 year. LSnow (late snow), snow on 

top of the current year’s summer surface, occurs only after the summer surface has formed. Found/left, total height on the stake before and after 

adjustments are made during a visit to improve its survivability. Obs. (observed) b', the average height on the stake of the glacier surface within a 

50-meter radius of the stake. b*, stake height of surveyed point on the stake near b'. b**, surveyed b* corrected for stake lean, bend, or bow. b*-

b**, value to be applied to correct b' for stake lean, bend, or bow. Total stake slip, cumulative distance the stake bottom has moved into the glacier 

since installed; it is generally assumed that the stake bottom is fixed in the glacier. Best b', observed b' corrected for stake lean, bend, bow, and/or 

slippage or, in other words, the calculated height of the glacier surface directly above the stake bottom (that is as if the stake were vertical). Stake 

d(s), snow depth as determined from the best b’ and previous or subsequent determinations of the stake height of the summer surface. Pit d(s), 

snow depth measured in snow pit. McCall d(s), snow depth measured with a McCall snow sampler, a small-diameter sampler used to core the 

entire snowpack. Probe d(s), snow depth measured by probing to the summer surface with a metal rod. Obs. d(s), observed snow depth measured 

directly on date without relying on stake readings from other dates. Mean d(s), average snow depth. s.e. d(s), standard error of snow depth. n, number of snow-depth samples. Snow density, measured in snow pit, by McCall snow sampler (a long, tube-type sampler), or estimated. m, meter; 

kg/L, kilograms per liter]

1 Site altitudes are approximate long-term averages rounded to the nearest 10 meters.

S t a k e d a t a S n o w d e p t h Snow density

Obs. b' Total Best

Surface Found no lean Surveyed Diff. stake stake Stake Pit McCall Probe Obs. Mean s.e. Pit McCall Est. Mean

Date Stake strata /left correct. b* b** b*-b** slip b' d (s) d (s) n d (s) n d (s) n d (s) d (s) d (s) n

(mm/dd/yyyy) name type (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (kg/L) (kg/L) (kg/L) (kg/L)

SITE A, 1,370 m 1

04/19/1996 96-A Snow 0/8 9.54 9.52 9.58 0.06 0.00 9.60 0.98 1 0.79 23 0.80 0.80 0.06 24 0.35 0.35

05/06/1996 96-A Snow 0.35 0.35

05/28/1996 96-A Snow 0.35 0.35

08/24/1996 96-A Ice

08/31/1996 96-A Ice 8/8 4.95 0.00 4.95 0.00 0.00 1

09/16/1996 96-A Ice 8/8 4.65 4.65 4.68 0.03 0.00 4.68 0.00 0.00 1

09/18/1996 96-A Ice

09/30/1996 96-A LSnow

04/18/1997 96-A Snow 8/6 5.85 5.85 5.88 0.03 0.00 5.88 1.43 3 1.29 20 1.31 1.31 0.06 23 0.35 0.35

04/16/1996 96-A1 Snow 0.35 0.35

04/19/1996 96-A1 Snow 0/8 9.49 9.47 9.48 0.01 0.00 9.50 0.98 1 0.79 23 0.80 0.80 0.06 24 0.35 0.35

05/28/1996 96-A1 Snow 0.35 0.35

08/24/1996 96-A1 Ice

08/31/1996 96-A1 Ice 8/8 5.00 0.00 5.00 0.00 0.00 1

09/16/1996 96-A1 Ice 8/8 4.66 4.73 4.74 0.01 0.00 4.67 0.00 0.00 1

09/18/1996 96-A1 Ice

09/30/1996 96-A1 LSnow

04/18/1997 96-A1 Snow 8/6 6.30 6.30 6.34 0.04 0.00 6.34 1.43 3 1.29 20 1.31 1.31 0.06 23 0.35 0.35

SITE B, 1,690 m 1

09/26/1995 94-B LSnow 9/9 4.61 4.60 4.55 0.05 0.00 4.56 0.15 2 0.15 18 0.15 0.15 0.01 20 0.42 0.42

09/30/1995 94-B LSnow

04/18/1996 94-B Snow 9/6 5.93 5.95 5.86 0.09 0.00 5.84 1.57 1 1.34 29 1.34 1.34 0.03 30 0.32 0.32

05/28/1996 94-B Snow 0.32 0.32

05/28/1996 94-B Snow 0.32 0.32

09/15/1997 94-B 6/0 -0.04

04/18/1996 96-B Snow 0/9 8.95 8.95 8.99 0.04 0.00 8.99 1.57 1 1.34 29 1.34 1.34 0.03 30 0.32 0.32

05/28/1996 96-B Snow 0.32 0.32

05/28/1996 96-B Snow 0.32 0.32

08/24/1996 96-B Ice

09/08/1996 96-B Ice

09/16/1996 96-B LSnow 9/11 6.74 6.72 6.75 0.03 0.00 6.77 0.25 3 0.15 21 0.16 0.16 0.01 24 0.31 0.31

09/30/1996 96-B LSnow

04/19/1997 96-B Snow 11/9 8.57 8.59 8.62 0.03 0.00 8.60 1.99 1.99 0.35 0.35

Site D, 1,840 m 1

09/26/1995 94-D LSnow 12/12 8.05 8.05 8.07 0.02 0.00 8.07 0.53 1 0.58 14 0.58 0.58 0.01 15 0.45 0.45

09/30/1995 94-D LSnow 0.45 0.45

04/18/1996 94-D Snow 12/12 10.03 10.03 10.02 0.01 0.00 10.02 2.29 1 2.39 16 2.39 2.39 0.02 17 0.48 0.48

05/28/1996 94-D Snow 0.48 0.48

05/28/1996 94-D Snow 0.48 0.48

08/21/1996 94-D Firn 0.36 0.36

08/24/1996 94-D LSnow 0.36 0.36

09/16/1996 94-D LSnow 12/12 9.14 9.22 9.25 0.03 0.00 9.17 0.68 2 0.68 0.68 0.02 2 0.36 0.36

09/30/1996 94-D LSnow 0.45 0.45

04/19/1997 94-D Snow 12/12 11.45 11.46 11.36 0.10 0.00 11.35 3.12 1 3.12 3.12 1 0.39 0.39

04/18/1996 96-D Snow 0/11 9.00 8.99 9.00 0.01 0.00 9.01 2.29 1 2.39 16 2.39 2.39 0.02 17 0.48 0.48

05/28/1996 96-D Snow 0.48 0.48

05/28/1996 96-D Snow 0.48 0.48

08/21/1996 96-D Firn 0.36 0.36

08/24/1996 96-D LSnow 0.36 0.36

09/16/1996 96-D LSnow 11/12 8.19 8.19 8.23 0.04 0.00 8.23 0.68 2 0.68 0.68 0.02 2 0.36 0.36

09/30/1996 96-D LSnow 0.45 0.45

04/19/1997 96-D Snow 11/11 10.64 10.66 10.67 0.01 0.00 10.65 3.12 1 3.12 3.12 1 0.39 0.39
16 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and runoff at Gulkana Glacier, 

Alaska, 1996 Balance

Table 8. Snow-temperature, firn-thickness, and firn-density data for index sites A, B, and D on Gulkana Glacier, September 1995 

through April 1997

[mm/dd/yyyy, month/day/year; LSnow (late snow), snow on top of the current year’s summer surface, occurs only after the summer surface has 

formed. Summer surface temperature, observed with dial (±1.0 °C) or digital (±0.1 °C) thermometer in snow pit or core sample. Est., estimated 

from previous measurements. Heights are above the stake bottom. Depths are measured from the glacier surface. Initial values are those at the 

beginning of the hydrologic year. Obs., observed values on a date, generally the difference between the best stake b' and multiple snow- or firndepth observations. Mean (stake heights), average stake height of a stratigraphic surface (summer surface) observed on different dates. b0', initial 

value (on October 1) of the height of a stratigraphic surface on the stake. d(nf), depth to bottom of first firn layer. Mean depth, average of all pit and 

probing depths for a given date. s.e., standard error; n, number of observations. ss1, first glacier summer surface down from the glacier surface (this 

is typically a bare ice surface in the ablation zone and a firn surface in the accumulation zone); ss2, second glacier summer surface down from the 

glacier surface (this is typically a firn surface; multiple summer surfaces only occur in the accumulation zone of the glacier). m, meter; kg/L, kilograms per liter]

1 Site altitudes are approximate long-term averages rounded to the nearest 10 meters.

Summer surface Stake height of Depth to bottom of Firn density Stake height of

temperature top of 1st firn 1st firn layer 1st firn bottom

Surface Pit or Est. Mean Initial Obs. Mean Pit Probe Mean s.e. Initial Obs. Est. Mean Initial Obs. Mean

Date Stake strata core b 0'ss1 b 'ss1 b 'ss1 ss1 Diff. d (nf) n d (nf) n d (nf) d (nf) n Pit b 0'ss2 b 'ss2 b 'ss2

(mm/dd/yyyy) name type (°C) (°C) (°C) (m) (m) (m) (m) (m) (m) (m) (m) (kg/L) (kg/L) (kg/L) (kg/L) (m) (m) (m)

SITE A, 1,370 m1

04/19/1996 96-A Snow - 5.2 - 5.2

05/06/1996 96-A Snow - 5.2 - 5.2

05/28/1996 96-A Snow - 5.2 - 5.2

08/24/1996 96-A Ice

08/31/1996 96-A Ice

09/16/1996 96-A Ice

09/18/1996 96-A Ice

09/30/1996 96-A LSnow

04/18/1997 96-A Snow

04/16/1996 96-A1 Snow - 5.2 - 5.2

04/19/1996 96-A1 Snow - 5.2 - 5.2

05/28/1996 96-A1 Snow - 5.2 - 5.2

08/24/1996 96-A1 Ice

08/31/1996 96-A1 Ice

09/16/1996 96-A1 Ice

09/18/1996 96-A1 Ice

09/30/1996 96-A1 LSnow

04/18/1997 96-A1 Snow

SITE B, 1,690 m1

09/26/1995 94-B LSnow

09/30/1995 94-B LSnow

04/18/1996 94-B Snow - 4.5 - 4.5

05/28/1996 94-B Snow - 4.5 - 4.5

05/28/1996 94-B Snow - 4.5 - 4.5

09/15/1997 94-B

04/18/1996 96-B Snow - 4.5 - 4.5

05/28/1996 96-B Snow - 4.5 - 4.5

05/28/1996 96-B Snow - 4.5 - 4.5

08/24/1996 96-B Ice

09/08/1996 96-B Ice

09/16/1996 96-B LSnow

09/30/1996 96-B LSnow

04/19/1997 96-B Snow

Site D, 1,840 m1

09/26/1995 94-D LSnow 0.0 0.0 7.42 7.49 7.58 0.08 0.91 1 0.91 1 0.59 0.63 0.63 7.16 7.16 7.42

09/30/1995 94-D LSnow 0.0 0.0 7.42 7.58 0.59 0.63 0.63

04/18/1996 94-D Snow - 5.1 - 5.1 7.58 7.63 7.58 0.05 0.63

05/28/1996 94-D Snow - 5.1 - 5.1 7.58 7.58 0.63

05/28/1996 94-D Snow - 5.1 - 5.1 7.58 7.58

08/21/1996 94-D Firn 7.58 8.36 0.63 0.48 0.48

08/24/1996 94-D LSnow 7.58 8.36 0.63 0.48 0.48

09/16/1996 94-D LSnow 7.58 8.49 8.36 1.39 2 1.58 24 1.57 0.06 26 0.63 0.48 0.48 7.16 7.60 7.58

09/30/1996 94-D LSnow 0.0 0.0 7.58 8.36 0.63 0.48 0.48

04/19/1997 94-D Snow -2.9 - 2.9 8.36 8.23 8.36 0.48 0.48 0.48

04/18/1996 96-D Snow - 5.1 - 5.1 6.64 6.62 6.64 0.63

05/28/1996 96-D Snow - 5.1 - 5.1 6.64 6.64 0.63

05/28/1996 96-D Snow - 5.1 - 5.1 6.64 6.64

08/21/1996 96-D Firn 6.64 7.54 0.63 0.48 0.48

08/24/1996 96-D LSnow 6.64 7.54 0.63 0.48 0.48

09/16/1996 96-D LSnow 6.64 7.55 7.54 0.01 1.39 2 1.58 24 1.57 0.06 26 0.63 0.48 0.48 6.66 6.64

09/30/1996 96-D LSnow 0.0 0.0 6.64 7.54 0.63 0.48 0.48

04/19/1997 96-D Snow -2.9 - 2.9 7.54 7.53 7.54 0.01 0.48 0.48 0.48
Glacier Mass Balance 17

Table 9. Ice data and mass-balance calculations for index sites A, B, and D on Gulkana Glacier, September 1995 through April 1997

[mm/dd/yyyy, month/day/year; LSnow (late snow), snow on top of the current year’s summer surface, occurs only after the summer surface has 

formed. Initial values are those at the beginning of the hydrologic year. Obs., observed values on a date, generally the difference between the best 

stake b' and multiple snow- or firn-depth observations. Mean (stake height), average stake height of a stratigraphic surface (summer surface) 

observed on different dates. Diff., the difference between the observed value and the mean value for that date, a good unbiased indication of the 

error in the stake height and snow- and firn-depth data at a site, commonly 0.05 to 0.15 meter; b0', initial value (on October 1) of the height of a 

stratigraphic surface on the stake; ss1, first glacier summer surface down from the glacier surface (this is typically a bare ice surface in the ablation 

zone and a firn surface in the accumulation zone); b0(s), initial snow balance (on October 1); b(s), snow balance; b(ls), late snow balance; b(f), firn 

balance; b(k), internal accumulation; b(i), ice balance; bn, net balance; ba, annual balance; bw(s), maximum winter snow balance; mwe, meters 

water equivalent (see Mayo and others (1972) for detailed explanation of this terminology)]

1 Site altitudes are approximate long-term averages rounded to the nearest 10 meters.

Stake height of top of ice M a s s b a l a n c e q u a n t I t I e s

Init. Late Int.

Surface Initial Obs. Mean snow Snow snow Firn acc. Ice Net Annual

Date Stake strata b 0'ss1 b 'ss1 b 'ss1 ss1 Diff. b 0(s) b (s) b (ls) b (f) b (k) b (i) b n b a

(mm/dd/yyyy) name type (m) (m) (m) (m) (mwe) (mwe) (mwe) (mwe) (mwe) (mwe) (mwe) (mwe) Notes

SITE A, 1,370 m1

04/19/1996 96-A Snow 8.80 8.80 8.80 0.00 0.28 0.00 0.00 0.00 0.00 0.28 0.28

05/06/1996 96-A Snow 8.80 8.80 0.00 0.30 0.00 0.00 0.00 0.00 0.30 0.30 Estimated local-site bw(s)

05/28/1996 96-A Snow 8.80 8.80 0.00 0.23 0.00 0.00 0.00 0.00 0.23 0.23 Estimated glacier-averaged bw(s)

08/24/1996 96-A Ice 8.80 5.31 0.00 0.00 0.00 0.00 0.00 - 3.14 -3.14 -3.14 Estimated glacier-averaged net mimimum

08/31/1996 96-A Ice 8.80 4.95 4.95 0.00 0.00 0.00 0.00 0.00 - 3.47 -3.47 -3.47

09/16/1996 96-A Ice 8.80 4.68 4.63 0.05 0.00 0.00 0.00 0.00 0.00 - 3.76 -3.76 -3.76

09/18/1996 96-A Ice 8.80 4.63 0.00 0.00 0.00 0.00 0.00 - 3.76 -3.76 -3.76 Estimated local-site net minimum

09/30/1996 96-A LSnow 8.80 4.63 0.00 0.04 0.04 0.00 0.00 - 3.76 0.04 -3.72 Estimated annual balance

04/18/1997 96-A Snow 4.63 4.57 4.63 0.05 0.04 0.46 0.00 0.00 0.00 0.00 0.46 0.42

04/16/1996 96-A1 Snow 8.70 8.70 0.00 0.30 0.00 0.00 0.00 0.00 0.30 0.30 Estimated local-site bw(s)

04/19/1996 96-A1 Snow 8.70 8.70 8.70 0.00 0.28 0.00 0.00 0.00 0.00 0.28 0.28

05/28/1996 96-A1 Snow 8.70 8.70 0.00 0.23 0.00 0.00 0.00 0.00 0.23 0.23 Estimated glacier-averaged bw(s)

08/24/1996 96-A1 Ice 8.70 5.21 0.00 0.00 0.00 0.00 0.00 - 3.14 -3.14 -3.14 Estimated glacier-averaged net mimimum

08/31/1996 96-A1 Ice 8.70 5.00 5.00 0.00 0.00 0.00 0.00 0.00 - 3.33 -3.33 -3.33

09/16/1996 96-A1 Ice 8.70 4.67 4.85 0.18 0.00 0.00 0.00 0.00 0.00 - 3.47 -3.47 -3.47

09/18/1996 96-A1 Ice 8.70 4.85 0.00 0.00 0.00 0.00 0.00 - 3.47 -3.47 -3.47 Estimated local-site bw(s)

09/30/1996 96-A1 LSnow 8.70 4.85 0.00 0.04 0.04 0.00 0.00 - 3.47 0.04 -3.43 Estimated annual balance

04/18/1997 96-A1 Snow 4.85 5.03 4.85 0.18 0.04 0.46 0.00 0.00 0.00 0.00 0.46 0.42

SITE B, 1,690 m1

09/26/1995 94-B LSnow 5.84 4.41 4.46 0.05 0.21 0.06 0.06 0.00 0.00 - 1.24 0.06 -1.39

09/30/1995 94-B LSnow 5.84 4.46 0.21 0.00 0.00 0.00 0.00 - 1.24 0.00 -1.45 Estimated annual balance

04/18/1996 94-B Snow 4.46 4.50 4.46 0.04 0.00 0.43 0.00 0.00 0.00 0.00 0.43 0.43

05/28/1996 94-B Snow 4.46 4.46 0.00 0.53 0.00 0.00 0.00 0.00 0.53 0.53 Estimated glacier-averaged bw(s)

05/28/1996 94-B Snow 4.46 4.46 0.00 0.53 0.00 0.00 0.00 0.00 0.53 0.53 Estimated local-site bw(s)

09/15/1997 94-B

04/18/1996 96-B Snow 7.65 7.65 7.65 0.00 0.43 0.00 0.00 0.00 0.00 0.43 0.43

05/28/1996 96-B Snow 7.65 7.65 0.00 0.53 0.00 0.00 0.00 0.00 0.53 0.53 Estimated glacier-averaged bw(s)

05/28/1996 96-B Snow 7.65 7.65 0.00 0.53 0.00 0.00 0.00 0.00 0.53 0.53 Estimated local-site bw(s)

08/24/1996 96-B Ice 7.65 6.74 0.00 0.00 0.00 0.00 0.00 - 0.82 -0.82 -0.82 Estimated glacier-averaged net mimimum

09/08/1996 96-B Ice 7.65 6.61 0.00 0.00 0.00 0.00 0.00 - 0.94 -0.94 -0.94 Estimated local-site net minimum

09/16/1996 96-B LSnow 7.65 6.61 6.61 0.00 0.05 0.05 0.00 0.00 - 0.94 0.05 -0.89

09/30/1996 96-B LSnow 7.65 6.61 0.00 0.11 0.11 0.00 0.00 - 0.94 0.11 -0.83 Estimated annual balance

04/19/1997 96-B Snow 6.61 6.61 0.11 0.70 0.00 0.00 0.00 0.00 0.70 0.59

Site D, 1,840 m1

09/26/1995 94-D LSnow 0.21 0.22 0.22 0.10 0.19 0.00 0.22 0.30

09/30/1995 94-D LSnow 0.21 0.23 0.23 0.10 0.19 0.00 0.23 0.31 Estimated annual balance

04/18/1996 94-D Snow 0.23 1.17 0.00 0.00 0.00 0.00 1.17 0.94

05/28/1996 94-D Snow 0.23 1.46 0.00 0.00 0.00 0.00 1.46 1.23 Estimated glacier-averaged bw(s)

05/28/1996 94-D Snow 0.23 1.46 0.00 0.00 0.00 0.00 1.46 1.23 Estimated local-site bw(s)

08/21/1996 94-D Firn 0.23 0.00 0.00 0.37 0.20 0.00 0.57 0.34 Estimated local-site net minimum

08/24/1996 94-D LSnow 0.23 0.01 0.01 0.37 0.20 0.00 0.01 0.35 Estimated glacier-averaged net mimimum

09/16/1996 94-D LSnow 0.23 0.29 0.29 0.37 0.20 0.00 0.29 0.63

09/30/1996 94-D LSnow 0.23 0.36 0.36 0.37 0.20 0.00 0.36 0.70 Estimated annual balance

04/19/1997 94-D Snow 0.36 1.18 0.00 0.00 0.00 0.00 1.18 0.82

04/18/1996 96-D Snow 0.23 1.14 0.00 0.00 0.00 0.00 1.14 0.91

05/28/1996 96-D Snow 0.23 1.46 0.00 0.00 0.00 0.00 1.46 1.23 Estimated glacier-averaged bw(s)

05/28/1996 96-D Snow 0.23 1.46 0.00 0.00 0.00 0.00 1.46 1.23 Estimated local-site bw(s)

08/21/1996 96-D Firn 0.23 0.00 0.00 0.43 0.20 0.00 0.63 0.40 Estimated local-site net minimum

08/24/1996 96-D LSnow 0.23 0.01 0.01 0.43 0.20 0.00 0.01 0.41 Estimated glacier-averaged net mimimum

09/16/1996 96-D LSnow 0.23 0.25 0.25 0.43 0.20 0.00 0.25 0.65

09/30/1996 96-D LSnow 0.23 0.36 0.36 0.43 0.20 0.00 0.36 0.76 Estimated annual balance

04/19/1997 96-D Snow 0.36 1.23 0.00 0.00 0.00 0.00 1.23 0.87
18 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Temporal extrapolations between measurements 

are necessary to estimate index-site balances such as 

the maximum winter balance, net balance, and annual 

balance. The extrapolations are made by a simple twoparameter linear model that relates the air temperature 

recorded at the Gulkana weather station and precipitation-gage catch (from Paxson through August 1996 

and from the Gulkana weather station for September 

1996) to the mass balance at each index site. The temperature is lapsed from the recorder altitude to each of 

the index-site altitudes using the wet-adiabatic lapse 

rate of -0.66 °C per 100 m. The model estimates glacier ablation at the rate of about 3.5 to 5 mm water 

equivalent per degree Celsius above 0 °C per day when 

the surface is snow and twice that when the surface is 

ice or old firn. This range of values agrees closely with 

those common in the literature (Braithwaite and 

Olesen, 1985, 1993; Braithwaite, 1995; Jóhannesson 

and others, 1995). Glacier accumulation is estimated 

by the model to be about 1.5 to 4.0 times the precipitation-gage catch when the lapsed temperature at the site 

is below 1.8 °C. 

The melt (ablation) rate and the precipitationcatch multipliers are not fixed. Separate values are 

determined for each measurement period at each index 

site so that the modeled balances always agree with the 

measured balances. Thus the model serves only to distribute the measured balance at each index site over 

each measurement interval. During the fall-to-spring 

measurement period, no ablation usually occurs, so the 

model is reduced to a one-parameter model dependent 

only on precipitation. During the spring-to-fall measurement period, little or no accumulation occurs, so 

the model again is reduced to a one-parameter model 

dependent only on temperature. Small quantities of 

accumulation early in the spring-to-fall measurement 

period are modeled using the precipitation-catch multiplier determined for the previous winter. Small quantities of accumulation near the end of the spring-to-fall 

measurement period are modeled by adjusting a separate precipitation-catch multiplier until the measured 

late snow balance is matched. 

Area-Averaged Balances

The three index-site balance values are combined 

using weighting factors to yield glacier-wide index 

values that approximate the average balances for the 

glacier area. Area-averaged balances are reported 

(table 10) using both the old (1967) and newer (1993) 

area altitude distributions to demonstrate how the balances are affected by the update. 

Using the 1967 area altitude distribution:

b = 0.193 (bA) + 0.224 (bB) + 0.583 (bD) + ba(j) . (6)

Using the 1993 area altitude distribution:

b = 0.171 (bA) + 0.202 (bB) + 0.627 (bD) + ba(j) , (7)

where b is the glacier-averaged balance, bA, bB, and bD

are measured index-site balance values, and ba(j) is 

glacier-averaged internal ablation. The weighting factors are derived by splitting the glacier into three subareas (index regions) at altitudes midway between the 

index sites (table 6). The fraction of total glacier area 

in each index region is the weighting factor for the 

index site within that region. Using this scheme, the 

weighting factors are allowed to change with time as 

the index-site altitudes and area altitude distribution 

change. However, prior to the work of March (2000), 

an unvarying area altitude distribution had been used 

as that was all that was available. As can be seen in 

equations 6 and 7, the loss of ablation area between 

1967 and 1993 results in a decrease in the weighting 

factor for sites A and B in the ablation zone and an 

increase in the weighting of site D in the accumulation 

zone. Overall, the change in weighting factors 

results in increases to the calculated glacieraveraged balances.

For the index-site weighting method to be valid, 

the index-site balance value should equal the average 

balance in the index region. March and Trabant (1996) 

applied the weighted index-site method to 1966 and 

1967 data and compared the results with the balances 

determined from detailed surface-balance mapping 

available for those years. The weighted index-site balances were found to be within the estimated errors of 

the mapped balances and suggest that glacier-averaged 

balance values determined using the weighted indexsite method have an error of ±0.2 m. The estimated 

error for 1996 could be larger than ±0.2 m due to 

changes in the area altitude distribution and changes in 

the gradient of mass balance with altitude since 1966 

and 1967. 

Because of the time- and space-transgressive 

nature of glacier balance, the bA, bB, and bD used to 

calculate a glacier-averaged balance, such as the net 

balance, may not be the same as the site net balances. 

This discrepancy occurs because when the glacieraveraged balance reaches its minimum, snow may 

have already accumulated at sites D and B. For 

instance, figure 4 shows both the local net balances 

that occurred on different dates at the different 
Glacier Mass Balance 19

Table 10. Index-site and area-integrated balance quantities for Gulkana Glacier and Gulkana Glacier Basin, 1996 hydrologic year, 

from both 1967 and 1993 area altitude distributions 

[m, meters; mm/dd/yyyy, month/day/year; km2, square kilometers; °C, degrees Celsius]

Parameter Site, glacier average, or subparameter Data Units

Year of area-altitude distribution determination = 1967 1993

Index-site weighting factors Site A 0.193 0.171

Site B 0.224 0.202

Site D 0.583 0.627

bn0 , initial net balance Site A -0.77 -0.77 (m)

Site B 0.00 0.00 (m)

Site D 0.00 0.00 (m)

Glacier average -0.15 -0.13 (m)

b0 (s), initial snow balance Site A -0.00 -0.00 (m)

Site B 0.00 0.00 (m)

Site D 0.23 0.23 (m)

Glacier average 0.13 0.14 (m)

b m (s), measured winter snow balance Date of measurement 04/18/1996 04/18/1996 (mm/dd/yyyy)

Site A 0.28 0.28 (m)

Site B 0.43 0.43 (m)

Site D 1.17 1.17 (m)

Glacier average 0.83 0.87 (m)

bw (s), maximum winter snow balance Date of maximum 05/28/1996 05/28/1996 (mm/dd/yyyy)

Site A 0.23 0.23 (m)

Site B 0.53 0.53 (m)

Site D 1.46 1.46 (m)

Glacier average 1.01 1.06 (m)

bnl , late net balance Site A 0.33 0.33 (m)

Site B 0.12 0.12 (m)

Site D 0.01 0.01 (m)

Glacier average 0.10 0.09 (m)

b1 (ls), final late snow balance Site A 0.04 0.04 (m)

Site B 0.11 0.11 (m)

Site D 0.36 0.36 (m)

Glacier average 0.24 0.25 (m)

ba (f), annual firn balance Site A 0.00 0.00 (m)

Site B 0.00 0.00 (m)

Site D 0.40 0.40 (m)

Glacier average 0.23 0.25 (m)

ba (k), annual internal accumulation Site A 0.00 0.00 (m)

Site B 0.00 0.00 (m)

Site D 0.20 0.20 (m)

Glacier average 0.12 0.13 (m)

ba (i), annual old firn and ice balance Site A -3.62 -3.62 (m)

Site B -0.94 -0.94 (m)

Site D 0.00 0.00 (m)

Glacier average -0.91 -0.81 (m)

ba (j), annual internal ablation (glacier averaged) From geothermal heat flux -0.005 -0.005 (m)

From potential energy loss from ice motion -0.005 -0.005 (m)

From potential energy loss from water flow (estimated) -0.035 -0.037 (m)

Total -0.04 -0.05 (m)

bn , net balance Start of net balance year for glacier average 08/30/1995 08/30/1995 (mm/dd/yyyy)

End of net balance year for glacier average 08/24/1996 08/24/1996 (mm/dd/yyyy)

Site A (09/29/1995 to 09/18/1996) -4.05 -4.05 (m)

Site B (08/30/1995 to 09/08/1996) -0.82 -0.82 (m)

Site D (08/30/1995 to 08/2119/96) 0.61 0.61 (m)

Glacier average (includes ba (j) ) -0.65 -0.53 (m)

ba , annual balance Site A -3.57 -3.57 (m)

Site B -0.83 -0.83 (m)

Site D 0.73 0.73 (m)

Glacier average (includes ba (j) ) -0.49 -0.37 (m)

ELA, equilibrium line altitude 1,768 1,768 (m)

Accumulation area 11.05 11.15 (km2

)

Ablation area 8.27 6.98 (km2

)

AAR, accumulation area ratio 0.57 0.61

Calculated annual precipitation Basin average 1.04 1.13 (m)

Annual basin runoff 1,125-meter stream gage 1.50 1.50 (m)
20 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

measurement sites and the August 26 estimated 

balances used to calculate the glacier-averaged 

net balance. 

The glacier-averaged internal ablation, ba(j), is 

calculated by combining three internal and subglacial 

energy sources: (1) the geothermal heat at the bed of 

the glacier, (2) the potential energy loss from ice 

motion, and (3) the potential energy loss from water 

flowing through the glacier and along the bed of the 

glacier (Mayo, 1992; March and Trabant, 1997). These 

terms are quite small annually (table 10) but, if 

neglected, would accumulate as a bias error over time.

Measured and Maximum Winter Snow Balances1

The measured winter snow balance, bm(s), is the 

snow balance measured to the previous summer surface during late winter or spring (Mayo and others, 

1972). It was 0.87 m on April 18, 1996 (fig. 11, 

table 10), using the 1993 area altitude distribution. 

This value was derived from the weighted index-site 

method and the April onsite-visit data (tables 7, 8, 

and 9). 

The maximum winter snow balance, bw(s), is the 

maximum snow mass during the balance year and may 

occur either before or after the measured winter snow 

balance (Mayo and others, 1972). It generally occurs 

after the time of the measured winter snow balance at 

Gulkana Glacier. The balance change between the 

time of the measured winter snow balance and the time 

of the glacier-averaged maximum winter snow balance 

is estimated for each index site by the simple balance 

model previously described. Following this method, 

the 1996 maximum winter snow balance was estimated to be 1.06 m (table 10) on May 28, 1996. 

Net Balance

Net balance is the change in snow, firn, and ice 

storage between times of minimum glacier-averaged 

mass (Mayo and others, 1972). The net balance, bn, at 

each index site is calculated directly from stake, pit, 

and probing data (tables 7, 8, and 9). Because of the 

time-transgressive nature of balance, the net balance at 

one site may not represent the same time period as the 

net balance at another site. Therefore, the simple linear 

balance model, discussed previously, is run to determine the glacier-averaged net balance on the basis of 

calculated site balances for the same time period. The 

net balance year ends almost a month earlier at sites B 

and D than it does at site A (fig. 4). The estimated 

balance at site A for August 29, 1995, which was used 

for calculating the glacier-averaged net balance, is also 

shown in figure 4. These calculated site balances differ 

from the tabulated net balances by small increments, 

which are the initial and late net balance increments, 

bn0 and bnl (table 9 and 10). Onsite measurements 

made near the end of the balance year are checked by 

and combined with measurements made during the 

next balance year before final values are assigned 

(tables 7, 8, and 9). The glacier-averaged net balance, 

bn, includes the additional balance term, internal ablation, which is not included in the net balances at individual sites. The 1996 net balance year began on about 

August 30, 1995, and ended on about August 24, 

1996; the net balance was -0.53 m (fig. 11, table 10).

Summer Balance

Summer balance is the algebraic difference 

between the winter balance, bw(s), and the net balance, 

bn (UNESCO/IASH, 1970)2

. The UNESCO/IASH 

definition of winter balance corresponds to the maximum winter balance term, bw(s), from Mayo and 

others (1972). Thus, the following equation defines the 

summer balance:

bs = bn - bw(s) = -1.59 m . (8)

Annual Mass Balance

Annual mass balance is the change in snow, firn, 

and ice storage between the beginning (October 1, 

1995) and end (September 30, 1996) of the hydrologic 

year. Evaluation of the 1996 annual balance required 

estimating two adjustment quantities for each index 

site: the initial snow balance, b0(s), at the beginning of 

1Mayo and others (1972) define three “winter” balance values 

in the stratigraphic system: the measured winter snow balance, 

m(s), the maximum winter snow balance, w(s), and the winter 

balance, w. The World Glacier Monitoring Service (WGMS) 

publishes a “winter” balance that is not clearly identified as any of 

these and may vary from glacier to glacier. The measured winter 

snow balance, m(s), is probably the most common “winter” 

balance value reported by WGMS.

b b

b

b 2The summer balance, bs, was not defined by Mayo and 

others (1972).
Glacier-Surface Altitude 21

the hydrologic year and the final late snow balance, 

b1(ls) (tables 9 and 10), at the end of the hydrologic 

year (Mayo and others, 1972). These quantities were 

estimated using the simple linear balance model discussed earlier. The 1996 annual balance at each index 

site, ba, is derived from the net balance and adjustment 

quantities: ba = bn - b0(s) + b1(ls) (table 9). The indexsite annual balances are combined using the weighted 

index-site method, with the addition of the internal 

ablation, to yield the 1996 annual balance, ba, of 

-0.37 m (table 10).

Accumulation Area Ratio and Equilibrium Line 

Altitude 

The accumulation area ratio (AAR) is the accumulation area of the glacier divided by the total area of 

the glacier. The accumulation area is the area of the 

glacier that undergoes net mass gain and includes 

areas of firn accumulation, superimposed ice, and 

areas where internal accumulation exceeds old firn 

loss. The 1996 AAR was 0.61 using the 1993 photogrammetry glacier-surface area and 0.57 using the 

1967 glacier-surface area determination (table 10).

The equilibrium line altitude (ELA) is the average 

altitude where the net mass balance is zero. Sometimes 

the ELA will correspond to the highest transient snow 

or firn line reached in the melt season (the line where 

snow ablation equals snow accumulation), but 

commonly the ELA is lower on the glacier because of 

internal accumulation in old firn or the presence of 

superimposed ice. The ELA seldom crosses a glacier 

along a single altitude contour. At Gulkana Glacier, 

the ELA can be extremely complicated, and its determination would require well-timed vertical or highangle oblique aerial photography to define it over the 

whole glacier. Obtaining this kind of photography near 

the time of formation of the ELA on a consistent basis 

year after year is impractical. Therefore, the ELA is 

calculated by linear interpolation from the balancealtitude curve of the three index sites. The 1996 ELA 

for Gulkana Glacier was determined to be 1,768 m 

(table 10). 

GLACIER-SURFACE ALTITUDE

The altitude of the glacier surface and the uppermost glacier summer surface at each index site is measured during each onsite visit (fig. 12, tables 11–12). 

At least three points on the glacier surface in the vicinity of each index site are optically surveyed. One of the 

points is placed as closely as possible to the index site. 

The mathematical plane defined by the three surveyed 

points is calculated as an approximation of the local 

Figure 11. Glacier-averaged measured winter balance, net balance, and summer balance, 1966–96, and smoothed data. 

Horizontal length of data symbols represents approximate time period of each data value. Smooth is an inverse distanceweighted smooth of the data using a 7-day window. 

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

1965 1970 1975 1980 1985 1990 1995 2000

BALANCE, IN METERS WATER EQUIVALEN

T

Measured winter

balance

Net

balance

Summer

balance
22 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

glacier surface. The altitude of this plane at the fixed 

horizontal position of the index site is calculated to 

determine the index-site altitude (Mayo and Trabant, 

1982). Snow depth is subtracted from the glacier surface to get the uppermost glacier summer surface altitude. The 1996 altitude data appeared to continue the 

glacier-wide thinning trend of the 1990s (fig. 12). 

Surveyed glacier-surface points typically have an 

altitude uncertainty of about ±0.05 m. Additionally, 

the locations used to define the plane of the glacier 

surface may not be representative of the average 

glacier surface; hence, extrapolating along this plane 

to the index site may introduce further error. The glacier-surface orientation and slope determinations have 

a small random variability that is used to assess the 

magnitude of this error. Although this error is sitespecific, depending largely on the local surface roughness of the glacier, an average glacier-surface-slope 

error of 0.5 grad was applied to the distance between 

the closest surveyed point and the index site. This 

error, combined with the surveying error, yielded an 

average error of ±0.15 m for the index-site altitudes. 

Figure 12. Glacier-surface altitudes at index sites A, B, and D. An unresolved datum shift exists between the 1975–87 data and the 

1988–96 data.

1,360

1,365

1,370

1,375

1,380

1,385

1,390

1,395

1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

ALTITUDE, IN METERS 

SITE A, ABLATION ZONE

1,830

1,835

1,840

1,845

1,850

1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

ALTITUDE, IN METERS 

SITE D, ACCUMULATION ZONE

1,675

1,680

1,685

1,690

1,695

1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998

ALTITUDE, IN METERS 

SITE B, NEAR EQUILIBRIUM LINE
Glacier-Surface Altitude 23

Table 11. Glacier-surface and summer-surface altitude measurements and analysis at index sites, Gulkana Glacier Basin, September 1995 to Sept[mm/dd/yyyy, month/day/year; P, Q, and R are three locations on the glacier surface near the index site determined by optical surveying. Xi, Yi are the horizontal lo

calculated altitude of the glacier surface at the index site. θ is the aspect of the glacier surface, with zero east and positive counterclockwise. φ is the slope of the gla

horizontal. Grad is a unit of measure for a plane angle and is equal to the plane angle in degrees multiplied by (100/90). Distance to closest point is the horizontal d

of points P, Q, or R. Zi error is the altitude error in Zi, derived by combining the resection errors with the error in extrapolating the glacier-surface altitude from the 

that the local glacier-surface slope is linear]

Table 12. Continuation of glacier-surface and summer-surface altitude measurements and analysis at index sites, Gulkana Glacier Basin, Septem[mm/dd/yyyy, month/day/year; stake name: the first two digits represent the year the stake was installed; letters (A, B, D) represent the index site on the glacier (figto differentiate multiple stakes installed at the same site in 1 year. Best b' is the height of the glacier surface directly above the stake bottom. Change in b' is the chan

current measurement. Emergence is the change in Zi minus the change in b' divided by the measurement period in years. Snow depth is the mean depth from the g

table 7). Zi(ss1) summer surface (altitude) at index site is Zi minus snow depth. m, meters; m/yr, meters per year]

 P Q R Index Site 

Index 

site Date X Y Z X Y Z X Y Z Xi Yi Zi 

(mm/dd/yyyy) (meters) (meters) (meters) (meters) 

09/26/1995 3,835.56 4,450.42 1,366.68 3,820.95 4,434.18 1,363.97 3,797.94 4,457.84 1,363.89 3,825.10 4,447.27 1,365.46 04/19/1996 3,814.47 4,445.02 1,366.44 3,801.35 4,476.66 1,367.62 3,792.21 4,451.28 1,365.00 3,825.10 4,447.27 1,367.50 09/16/1996 3,822.09 4,443.95 1,362.88 3,804.77 4,464.37 1,363.39 3,808.81 4,449.59 1,362.40 3,825.10 4,447.27 1,363.39 09/26/1995 4,722.55 7,383.93 1,679.46 4,723.78 7,354.50 1,676.94 4,737.67 7,369.04 1,678.94 4,728.61 7,391.17 1,680.41 04/18/1996 4,743.93 7,419.85 1,684.96 4,731.76 7,389.68 1,681.78 4,731.96 7,427.31 1,685.16 4,728.61 7,391.17 1,681.79 09/16/1996 4,731.70 7,386.11 1,679.22 4,735.00 7,402.25 1,680.77 4,712.56 7,391.72 1,678.91 4,728.61 7,391.17 1,679.53 09/26/1995 5,997.81 7,355.60 1,832.13 5,979.49 7,367.49 1,830.09 5,983.16 7,381.16 1,829.81 5,999.01 7,353.57 1,832.32 04/18/1996 5,987.59 7,360.72 1,832.46 5,993.84 7,371.10 1,832.77 6,021.61 7,345.60 1,836.07 5,999.01 7,353.57 1,833.73 09/16/1996 5,964.75 7,356.25 1,828.36 6,001.91 7,350.75 1,832.38 5,970.61 7,379.27 1,829.16 5,999.01 7,353.57 1,832.08 

Site A Site B Site D

Stake 1 Stake 2 Stake 3 Stake 4 

Index Change Change Change Change Average Emergenc

site Date Name Best b' b' Name Best b' b' Name Best b' b' Name Best b' b' emergence rate 

(mm/dd/yyyy) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m/yr) 

09/26/1995 95-A 3.89 -6.29 95-A2 4.27 -5.87 1.90 4.33 04/19/1996 96-A 9.60 96-A1 9.50 95-A 4.97 1.08 95-A2 5.27 1.00 1.00 1.77 

09/16/1996 96-A 4.68 -4.92 96-A1 4.67 -4.83 0.77 1.86 09/26/1995 94-B 4.56 -3.47 0.34 0.78 04/18/1996 94-B 5.84 1.28 96-B 8.99 0.10 0.19 09/16/1996 96-B 6.77 -2.22 -0.04 - 0.10 09/26/1995 93-D 6.36 94-D 8.07 -2.06 -0.98 - 2.24 04/18/1996 94-D 10.02 1.95 96-D 9.02 -0.54 - 0.96 09/16/1996 94-D 9.17 -0.85 96-D 8.23 -0.79 -0.83 - 2.00 

Site A Site B Site D
24 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

Index-site errors were calculated separately for each 

measurement and are included in table 11. 

Emergence (table 12), the change in the glacier 

surface altitude due to ice motion, showed the normally expected positive emergence in the ablation 

zone (compressing flow), submergence in the 

accumulation zone (extending flow), and intermediate 

values near the ELA.

ICE MOTION

Surface-ice displacements near the fixed index 

sites are measured by optical surveying of balancemotion stakes. The stakes are installed about 1 year's 

flow displacement upglacier from each index site. 

Replacement stakes are installed every year or two. 

Thus, the stakes are kept within 1 year’s displacement 

of the index site (usually less than 80 m) to maximize 

the year-to-year comparability of the motion and altitude data (Mayo and others, 1979; Mayo and Trabant, 

1982). Reported stake-motion data have been corrected for changes in stake geometry (table 13; see 

March, 2000). 

The position of the bottom of the stake is determined by surveying two points on each stake (one at 

the glacier surface and the other 1 or 2 m higher on the 

stake) and calculating the location of the stake bottom 

using a lean (linear), bend (multiple straight sections 

separated by sharp bends), or bowed (gradual bend 

spread out over a meter or more) stake geometry. In 

the long history of field observations at Gulkana Glacier, it has been rare to find bent or bowed melted-out 

stakes, so a “lean” geometry generally is assumed 

unless the stake is severely tilted. Occasionally, when 

a stake is severely tilted, it is partly excavated to determine if it is bent or bowed, and where. Some of the 

stakes tend to straighten as they are dug up and the 

snow-creep load is removed, a sign that the stake was 

elastically bowed. Three-meter sections of the 2.5-cmdiameter thinwall EMT conduit used for stakes can be 

elastically bowed about 13 grads (an arc radius of 

about 15 m). When a bend or bow does occur, it is 

generally at or above the most-recent summer surface. 

Location uncertainty is largely a result of the survey-control net errors (GPS for horizontal and optical 

surveying for vertical) and resection survey errors. 

Resection surveys are conducted by surveying four or 

five backsight targets, instead of the minimum of three 

backsight targets, to allow error evaluation. The net 

and resection errors combined yield position errors of 

about ±0.15 m in the horizontal and ±0.05 m in the 

vertical. The error of extrapolating to the bottom of the 

stake is estimated to be ±0.15 m, resulting in a total 

horizontal error for stake-bottom positions of ±0.2 m. 

Vertical errors are significantly less, about ±0.05 m. 

Hence, reported displacements have errors of about

±0.3 m. 

Ice motion this year was 40 to 50 m/yr in the central reach of the glacier and about one-half that in the 

lower ablation zone. There has been a general slowing 

trend through the 1990s with a reduction of about 

20 percent since 1990 and about 5 percent since 1995.

TERMINUS POSITION 

On August 31 and September 1, 1996, 126 locations along the lower glacier margin were surveyed 

with a handheld Collins Rockwell Precision Lightweight GPS Receiver (PLGR+) to define the glacier 

terminus and lower ablation area for 1996 (fig. 13, 

table 14). The Collins Rockwell PLGR+ is a militarygrade, single-frequency (L1) encrypted P(Y) code 

GPS receiver capable of Precise Positioning Service 

(PPS) operation. PPS, as opposed to the Standard 

Positioning Service (SPS) used by civilian GPS receivers, uses encrypted signals to correct for the deliberate 

GPS signal degradation of Selective Availability (SA) 

that was active until May 2, 2000. 

The instrument has a stated positioning accuracy 

of less than 16 m spherical error probable (SEP) using 

PPS and less than 4 m circular error probable (CEP) 

with its firmware Wide Area GPS Enhancement 

(WAGE) feature activated (processes enhanced clock 

corrections). (Error probable corresponds to a 

50-percent confidence interval.) In an assessment of 

recent GPS enhancements to the satellite-broadcast 

navigation message, Wilson and others (1999) report 

PLGR errors of about 4.5 m horizontal and 6 m 

vertical prior to April 1999 and about 4.5 m horizontal 

and 5 m vertical after that date. To partially check the 

PLGR’s accuracy during the survey, an off-glacier survey monument (Péwé, fig. 13) along the walk in to the 

terminus (NAD 83 UTM Easting 576816.78 m, Northing 7012770.41 m, NGVD 29 altitude 1,152.7 m), was 

surveyed at the beginning and end of each 3- to 

6-hour-long terminus survey. Horizontal errors at 

Péwé varied from 1 to 5 m and averaged 3 m. The vertical errors (bias) varied from -9 to 3 m and averaged 

-3 m. Some concern exists over the applicability of 

errors measured at Péwé because the valley is more 
Terminus Position 25

Table 13. Stake locations, stake lean corrections, and motion determined from optical surveys, September 1995 to September 1996[mm/dd/yyyy, month/day/year; stake name: the first two digits represent the year the stake was installed; letters (A, B, D) represent the index site on the glacier (fig. 2

to differentiate multiple stakes installed at the same site in 1 year. Xg, Yg, Zg, stake lower target is where the stake intersects the glacier surface. Xt, Yt, Zt, stake upp

2.0 meters above the glacier surface. Ht is the height of the stake upper target above the stake bottom as measured along the stake. θ is the downdip direction with ze

φ is the dip angle with zero horizontal and positive angles up. Solution type: lean, treats the stake as a linear segment; bend, treats the stake as multiple linear segmen

is the calculated height of the stake lower target above the stake bottom as measured along the stake. b** is the calculated height of the glacier surface directly abov

vertical). dXYZ is the total three-dimensional displacement of the stake bottom between measurements. Speed is the stake displacement divided by the measuremenment angle is measured positive counterclockwise; zero is east. Vertical displacement angle is measured positive up from horizontal. grad is a unit of measure for a 

angle in degrees multiplied by (100/90). m, meters; m/yr, meters per year]

Index Stake lower target Stake upper target Glacier surface Bend Solution Stake angles Stake angles Stake bottom 

site Date Stake Xg Yg Zg Xt Yt Zt Ht θ φ depth type θ 1 φ 1 θ φ Xs Ys Zs b* 

(mm/dd/yyyy) Name (m) (m) (m) (m) (m) (m) (m) (grad) (m) (grad) (grad) (m) (m) (m) (m) 

09/26/1995 95-A 3,797.94 4,457.84 1,363.89 3,798.55 4,458.10 1,366.10 6.50 -152.13 -7.89 lean -174.35 -81.44 3,796.83 4,457.37 1,359.88 4.19 

04/17/1996 95-A 3,792.21 4,451.28 1,365.00 3,792.63 4,451.48 1,366.62 7.00 -154.98 -7.09 lean -171.71 -82.20 3,790.89 4,450.65 1,359.90 5.31 

09/26/1995 95-A2 3,802.49 4,453.43 1,364.01 3,802.82 4,453.11 1,366.09 6.50 -152.13 -7.89 lean 150.98 -86.15 3,801.81 4,454.09 1,359.74 4.37 04/17/1996 95-A2 3,796.61 4,446.54 1,365.04 3,796.83 4,446.24 1,366.60 7.00 -154.98 -7.09 lean 140.28 -85.10 3,795.87 4,447.55 1,359.79 5.40 04/17/1996 96-A 3,801.35 4,476.66 1,367.62 3,801.24 4,476.57 1,369.08 11.00 -154.98 -7.09 lean 43.65 -93.82 3,802.06 4,477.24 1,358.13 9.53 

09/16/1996 96-A 3,796.12 4,470.85 1,363.03 3,795.95 4,470.74 1,365.36 7.00 -144.54 -7.23 lean 36.56 -94.48 3,796.46 4,471.07 1,358.39 4.66 

04/17/1996 96-A1 3,810.23 4,470.56 1,367.88 3,810.18 4,470.59 1,369.41 11.00 -154.98 -7.09 lean - 34.40 -97.57 3,810.54 4,470.37 1,358.42 9.47 

09/16/1996 96-A1 3,804.77 4,464.37 1,363.39 3,804.76 4,464.34 1,365.66 7.00 -144.54 -7.23 lean 79.52 -99.11 3,804.79 4,464.43 1,358.66 4.73 

09/26/1995 94-B 4,723.78 7,354.50 1,676.94 4,723.51 7,354.64 1,678.82 6.50 -133.91 -6.47 lean - 30.45 -89.79 4,724.43 7,354.16 1,672.40 4.60 04/18/1996 94-B 4,716.09 7,335.49 1,676.34 4,715.69 7,335.57 1,678.35 8.00 -126.32 -6.21 lean - 12.57 -87.25 4,717.25 7,335.26 1,670.51 5.95 

04/18/1996 96-B 4,743.93 7,419.85 1,684.96 4,743.83 7,419.71 1,687.01 11.00 -126.32 -6.21 lean 60.51 -94.67 4,744.36 7,420.46 1,676.05 8.94 

09/16/1996 96-B 4,735.00 7,402.25 1,680.77 4,734.91 7,402.11 1,683.03 9.00 -128.51 -6.16 lean 63.63 -95.32 4,735.27 7,402.67 1,674.06 6.73 

09/26/1995 94-D 5,979.49 7,367.49 1,830.09 5,979.22 7,367.65 1,832.01 10.00 169.98 -5.96 lean - 34.06 -89.68 5,980.61 7,366.83 1,822.15 8.05 

04/18/1996 94-D 5,957.60 7,380.43 1,829.27 5,957.10 7,380.66 1,831.15 12.00 182.35 -6.21 2.39 bend - 27.45 -89.68 - 27.45 -81.87 5,959.33 7,379.63 1,819.43 10.04 

09/16/1996 94-D 5,939.62 7,391.14 1,826.12 5,939.47 7,391.22 1,827.39 10.50 -196.04 -6.94 lean - 31.19 -91.53 5,940.70 7,390.56 1,816.98 9.22 04/18/1996 96-D 6,020.25 7,339.93 1,835.75 6,020.21 7,339.98 1,837.76 11.00 182.35 -6.21 lean - 57.04 -97.97 6,020.43 7,339.71 1,826.76 8.99 

09/16/1996 96-D 6,001.91 7,350.75 1,832.38 6,001.80 7,350.78 1,834.20 10.00 -196.04 -6.94 lean - 16.95 -96.02 6,002.40 7,350.62 1,824.22 8.18 

Site A Site B Site D
26 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

open here than at the glacier terminus and hence the 

satellite constellation visibility is better. Estimated 

horizontal PLGR errors recorded at locations on the 

terminus during surveys other years are summarized 

here to help assess the applicability of the errors determined by Wilson and others (1999) and by our measurements at Péwé. The average horizontal error was 

5 to 6 m for approximately 180 terminus locations surveyed in 1999 and 2000. About 5 percent of the errors 

were greater than 10 m, and the maximum errors were 

15 and 20 m, respectively, in the 2 years. We conclude 

that the average horizontal and vertical error was ±6 m 

for the 1996 terminus data.

PLGR elevations were referenced to the WGS 84 

(World Geodetic System 1984) geoid model, a mathematical approximation to mean sea level. A correction 

of 9 m was subtracted from these altitudes to yield the 

reported altitudes (table 14) in the NGVD 29 datum so 

as to be compatible with previous Gulkana Glacier 

publications. This correction is based on survey-grade 

GPS and optical surveys of 12 locations in the 

glacier basin. 

In 1996, surveyed locations were spaced an average of 30 m apart. The total distance surveyed along 

the glacier terminus was about 4 km. 

Debris covers much of the terminus (fig. 3). In 

some areas, the downvalley transition from clean 

Figure 13. Glacier terminus positions from Global Positioning System surveys on August 31 and September 1, 1996, 

and from U.S. Geological Survey 1:63,360-scale Mt. Hayes A3 quadrangle (1949 photography; area south of about 

7,014,200 m Northing) and B3 quadrangle (1954 photography; area north of about 7,014,200 m Northing) digital raster 

graphic (DRG) files. DRG files were converted from NAD 27 datum to NAD 83 datum. (Shaded area indicates large 

uncertainty in defining terminus position. Coordinates are Universal Transverse Mercator, datum is NAD 83.)

Site A

Weather

station

Péwé

7,012,500

7,013,000

7,013,500

7,014,000

7,014,500

7,015,000

7,015,500

7,016,000

576,500 577,000 577,500 578,000 578,500 579,000 579,500 580,000

EASTING, IN METERS

NORTHING, IN METERS

1949-54

August 31, 1996

September 1, 1996
Terminus Position 27

Table 14. Global Positioning System terminus-position surveys at Gulkana Glacier on August 31 and September 1, 1996

[UTM coordinates are in UTM zone 6. Coordinates in parentheses indicate large uncertainty in defining terminus position. m, meters; 

NAD 83, North American Datum of 1983; NGVD 29, National Geodetic Vertical Datum of 1929] 

UTM (zone 6) - NAD 83 NGVD 29 UTM (zone 6) - NAD 83 NGVD 29 UTM (zone 6) - NAD 83 NGVD 29

Easting Northing Altitude Easting Northing Altitude Easting Northing Altitude

(m) (m) (m) (m) (m) (m) (m) (m) (m)

August 31, 1996 August 31, 1996 - Continued September 1, 1996

Péwé: 579,407 7,015,270 1,370 Péwé:

576,816 7,012,769 1,145 579,451 7,015,344 1,383 576,813 7,012,773 1,144

576,816 7,012,767 1,146 579,493 7,015,411 1,392 576,813 7,012,774 1,146

576,816 7,012,768 1,144 579,529 7,015,471 1,400 576,813 7,012,773 1,144

576,817 7,012,768 1,144 579,585 7,015,536 1,408 Terminus positions:

Terminus positions: 579,648 7,015,623 1,415 578,155 7,014,492 1,179

578,199 7,014,479 1,177 579,697 7,015,684 1,417 578,131 7,014,493 1,159

578,217 7,014,472 1,180 579,707 7,015,704 1,421 578,123 7,014,505 1,157

578,252 7,014,485 1,183 (578,096) (7,014,514) 1,158

578,274 7,014,491 1,183 578,353 7,015,758 1,338 (578,075) (7,014,514) 1,155

578,283 7,014,492 1,181 578,336 7,015,729 1,329 (578,088) (7,014,537) 1,181

578,274 7,014,478 1,182 578,322 7,015,707 1,321 (578,067) (7,014,549) 1,181

578,262 7,014,462 1,182 578,156 7,015,542 1,280 (578,041) (7,014,524) 1,180

578,268 7,014,443 1,186 578,137 7,015,523 1,278 (578,022) (7,014,517) 1,173

578,285 7,014,442 1,186 578,100 7,015,482 1,272 (577,963) (7,014,514) (1,171)

578,301 7,014,462 1,187 578,075 7,015,453 1,262 (577,901) (7,014,528) (1,170)

578,310 7,014,465 1,188 578,069 7,015,438 1,259 (577,884) (7,014,545) (1,172)

578,313 7,014,468 1,187 578,067 7,015,423 1,254 (577,883) (7,014,574) (1,173)

578,316 7,014,454 1,188 578,065 7,015,427 1,233 (577,885) (7,014,615) (1,175)

578,331 7,014,463 1,189 578,077 7,015,418 1,234 (577,889) (7,014,666) (1,182)

578,329 7,014,449 1,187 578,099 7,015,400 1,236 (577,896) (7,014,695) (1,182)

578,349 7,014,454 1,189 578,100 7,015,391 1,236 (577,914) (7,014,710) (1,184)

578,360 7,014,451 1,190 578,106 7,015,378 1,231 (577,901) (7,014,737) (1,186)

578,426 7,014,463 1,195 578,111 7,015,356 1,237 (577,888) (7,014,757) (1,189)

578,456 7,014,472 1,200 578,111 7,015,309 1,231 (577,863) (7,014,868) (1,205)

578,482 7,014,472 1,201 578,104 7,015,264 1,227 (577,863) (7,014,869) (1,206)

578,570 7,014,495 1,235 578,099 7,015,215 1,225 (577,875) (7,014,933) (1,215)

578,582 7,014,502 1,236 (578,084) (7,015,161) (1,224) (577,963) (7,015,024) (1,220)

578,597 7,014,514 1,233 (578,036) (7,015,070) (1,221) (577,989) (7,015,045) (1,221)

578,623 7,014,525 1,237 (578,006) (7,014,997) (1,221) (578,022) (7,015,081) (1,224)

578,645 7,014,537 1,242 (577,994) (7,014,922) (1,217) (578,044) (7,015,106) (1,225)

578,662 7,014,546 1,244 (577,900) (7,014,747) (1,177) (578,054) (7,015,132) (1,226)

578,693 7,014,564 1,248 (577,912) (7,014,709) (1,174) (578,082) (7,015,162) (1,226)

578,729 7,014,588 1,255 (577,953) (7,014,660) (1,178) 578,099 7,015,190 1,224

578,750 7,014,593 1,257 (578,007) (7,014,656) (1,182) 578,099 7,015,203 1,225

578,778 7,014,614 1,262 (578,003) (7,014,603) (1,175) 578,096 7,015,220 1,227

578,819 7,014,648 1,269 (578,075) (7,014,620) (1,175) 578,100 7,015,235 1,228

578,876 7,014,675 1,274 (578,114) (7,014,594) (1,176) 578,098 7,015,256 1,230

578,914 7,014,712 1,278 (578,077) (7,014,552) (1,164) 578,104 7,015,273 1,230

578,956 7,014,729 1,282 (578,097) (7,014,512) (1,164) 578,108 7,015,294 1,231

578,985 7,014,742 1,285 578,121 7,014,501 1,162 578,115 7,015,316 1,241

579,020 7,014,762 1,290 578,136 7,014,493 1,162 578,109 7,015,340 1,239

579,064 7,014,792 1,297 578,156 7,014,495 1,162 578,112 7,015,366 1,240

579,119 7,014,832 1,306 Péwé: 578,107 7,015,380 1,236

579,169 7,014,875 1,311 576,813 7,012,769 1,152 Péwé:

579,216 7,014,926 1,318 576,812 7,012,769 1,150 576,818 7,012,772 1,155

579,241 7,014,973 1,323 576,812 7,012,768 1,149 576,818 7,012,770 1,150

579,247 7,015,016 1,330 576,813 7,012,769 1,153 576,818 7,012,770 1,150

579,286 7,015,084 1,342 576,813 7,012,768 1,154 576,817 7,012,771 1,153

579,322 7,015,146 1,352 576,813 7,012,768 1,153

579,359 7,015,202 1,361
28 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

glacier ice to debris-covered active glacier ice to stagnant ice-cored moraine and finally to a proglacial till is 

very gradual and indistinct. In such areas, it is 

extremely difficult to identify the location of the glacier terminus either on the ground or on stereo aerial 

photographs. In particular, there is a 0.5-km area of the 

southwest terminus (shaded area in figure 13 and locations in parentheses in table 14) where the error in 

defining the terminus is large, possibly as great as 

200 m. The terminus position in this area was surveyed on 2 different days. The difference in the positions for the 2 days is due mostly to the error in 

deciding where the terminus is. Instrument error and 

real terminus-position change between the two surveys 

are negligible at the plotted scale in figure 13. Elsewhere the terminus position generally can be defined 

within 1 to 2 m on the ground. 

For terminus change, the USGS 1:63,360-scale 

digital raster graphic (DRG) file for the Mt. Hayes A3 

quadrangle, which shows the terminus position in 

1949 (aerial photograph date) for the lowest 1.5 km of 

the glacier, was examined. The DRG terminus position 

was traced in its NAD 27 datum and then converted to 

NAD 83 for comparison with the 1996 GPS survey 

(fig. 13). U.S. National Map Accuracy Standards for 

1:63,360-scale maps would indicate the horizontal 

standard error is ±20 m, but errors may be greater as it 

is not stated on these quadrangle maps that they meet 

the standard. From 1949 to 1996, the terminus 

retreated about 1,650 m for an average retreat rate of 

35 m/yr. 

RUNOFF

Stream-gaging station 15478040, Phelan Creek 

near Paxson3

, is part of the USGS stream-monitoring 

network in Alaska. Data collection and analysis are 

conducted by standard techniques developed by the 

USGS, and daily values of discharge generally are 

reported along with those for the rest of Alaska in the 

annual USGS Water-Data Report series (U.S. 

Geological Survey, 1968–97; see also 

http://ak.water.usgs.gov/glaciology/gulkana/

streamflow/).

The gaging station is located at 1,125 m, about 

1 km downstream from the present glacier terminus 

(figs. 2 and 3). The creek bed consists of poorly sorted 

gravel and small boulders. The channel is subject to 

frequent changes during high flows. Typical winter 

under-ice discharge is about 0.1 m3/s; typical summer 

discharge ranges from 4 to 20 m3

/s; the period-ofrecord peak discharge is 65 m3/s (Linn and others, 

1997). The typical minimum winter discharge is about 

0.04 m3/s, which is about three to four times the 

average contribution from the combined geothermal 

melt of the bed of the glacier and melting caused by 

ice motion. 

Stream stage is continuously recorded, and discharge measurements are made periodically to determine the relation between stage and discharge at 

different streamflows and to detect any shifts in the 

relation due to changes in the creek bed. Because of 

the low frequency of discharge measurements 

(fig. 14), the poor quality of gage-height record, and 

the changeable nature of the creek bed, the published 

discharge record is rated as "poor," meaning that less 

than 95 percent of the daily discharges are within 

15 percent of the true value (Linn and others, 1997). 

This published rating places no limit on the possible 

error but indicates that the standard error is greater 

than ±7.5 percent. The standard error of the daily discharge values at Phelan Creek gaging station is estimated at 10 percent normally and 20 percent for the 

few values estimated during open-water conditions 

(Richard Kemnitz, USGS, oral commun., 1997). 

The 1996 discharge record was reported with the 

rest of the 1996 Alaska water data in the USGS WaterData Report AK–96–1 (Linn and others, 1997). The 

1996 daily mean discharge data were converted to runoff (fig. 14, table 15) by dividing the discharge values 

by the basin area. The 1996 runoff was 1.50 m, 

approximately 1.0 standard deviation below the 

period-of-record (1967–78, 1990–96) average. New 

record-high daily runoff occurred on June 19–20 following record-high temperatures on June 18–19. New 

record-low daily runoffs occurred during cold snaps 

on June 11–12, 30, July 1, and August 7; the August 7 

record low followed a new record-low daily temperature on August 6.

Runoff values were estimated for the ice period 

on the basis of air temperature, precipitation, and 

winter discharge measurements (November 9, 1995, 

February 1, 1996, and April 19, 1996). The relation 

between estimated daily runoff and the winter discharge measurements (converted to daily runoff) for 

the current year and for the entire period of record is 

3Before October 1968, data for this station were published as 

"Gulkana Creek near Paxson."
Summary 29

shown in figure 15. New estimated record high daily 

runoff values occurred during most of the winter from 

October 20, 1995, to February 11, 1996, but previous 

record highs were exceeded only by 0.1 to 0.2 mm/d. 

Because the discharge measurements are so sparse in 

any 1 year, display of these measurements for the 

entire period of record is useful to help gage the possible error in these estimates. The range of measured 

values over the entire period of record suggests that 

the standard error in the estimates from October into 

early May is less than ±0.2 mm/d, but then the error 

rapidly increases with the onset of the melt season in 

mid-May to about ±5 mm/d by early June. The 

cumulative sum of estimated winter runoff represents 

about 15 percent of the annual runoff. 

SUMMARY

The 1996 measured winter snow, maximum winter 

snow, net, and annual balances in the Gulkana Glacier 

Basin were evaluated on the basis of meteorological, 

hydrological, and glaciological data. Averaged over 

the glacier, the measured winter snow balance was 

0.87 m on April 18, 1996, 1.1 standard deviation or 

0.27 m below the long-term average; the maximum 

winter snow balance, 1.06 m, was reached on May 28, 

1996; and the net balance (from August 30, 1995, to 

August 24, 1996) was -0.53 m, 0.53 standard deviation 

or 0.27 m below the long-term average. The annual 

balance (October 1, 1995, to September 30, 1996) was 

-0.37 m. Area-averaged balances were reported using 

both the 1967 and 1993 area altitude distributions (the 

numbers previously given in this summary use the 

1993 area altitude distribution). Net balance was about 

25 percent less negative using the 1993 area altitude 

distribution than the 1967 distribution. 

The annual average air temperature sensed with 

the analog sensor at 1,480 m was -5.0 °C, 0.9 standard 

deviations below the long-term average. In the first 

year of use, the digitally sensed annual average air 

temperature was 0.9 °C warmer than that recorded 

with the analog sensor used since 1966. Total precipitation catch for the year was 0.78 m, 0.8 standard deviations below normal. Despite a wind shield, the gage’s 

Figure 14. Daily runoff from Phelan Creek near Paxson (USGS stream-gaging station 15478040), 1996 hydrologic year. Large 

filled circles are instantaneous discharge measurements, expressed as runoff, that are used to define the stage-discharge 

relation. Also shown are the record-high, average, and record-low daily runoff for the period of record (1967–78, 1990–96).

Phelan Creek Stream-Gaging Station

Period of Record: 1967-78, 1990 to 1995

0

10

20

30

40

50

60

70

80

90

100

DAILY RUNOFF, IN MILLIMETERS

Record low

Record high

Average

1996 

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
30 Mass Balance, Meteorology, Area Altitude Distribution, Glacier-Surface Altitude, Ice Motion, Terminus Position, and Runoff at Gulkana Glacier, 

Alaska, 1996 Balance Year

catch efficiency is strongly affected by wind. Catch 

efficiency averages about 0.57. The annual average 

wind speed was 3.5 m/s. 

Glacier-surface altitude and ice-motion changes 

measured at three index sites document glacier-thickness and seasonal ice-speed changes. The 1996 glacier-surface altitude data continued the glacier-wide 

thinning trend of the 1990s. Ice motion in the central 

reach of the glacier was 40 to 50 m/yr with a slow 

down in the lower ablation zone to about one-half that. 

There has been a general slowing trend through the 

1990s with a reduction of about 20 percent since 1990 

and about 5 percent since 1995. 

The glacier terminus and lower ablation area were 

defined for 1996 with a handheld GPS survey of 

126 locations spread out over about 4 km of the lower 

glacier margin. From 1949 to 1996, the terminus 

retreated about 1,650 m for an average retreat rate of 

35 m/yr. Annual stream runoff averaged 1.50 m over 

the basin, 1.0 standard deviation below the long-term 

average. 

REFERENCES CITED

Barry, R.G., 1989, Climate of the Arctic Ocean, in Herman, 

Y., ed., The Arctic Seas—climatology, oceanography, 

geology, and biology: New York, Van Nostrand Reinhold, p. 1–46. 

Table 15. Daily mean runoff from the Gulkana Glacier Basin, 1996 hydrologic year

[Values in millimeters, averaged over the basin; except standardized values which are in units of standard deviation; () indicates value estimated 

(see text for explanation)]

1995 1996

Day Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Annual

1 3.3 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 8.3 6.0 25.1 11.2

2 2.7 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 9.1 6.3 24.2 ( 9.3)

3 2.3 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.3) 9.5 10.8 18.1 ( 9.3)

4 2.0 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.3) 7.4 10.4 16.1 10.1

5 1.8 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.3) 5.7 15.2 15.1 ( 7.7)

6 1.6 ( 0.9) ( 0.6) ( 0.5) 0.4 ( 0.3) ( 0.3) ( 0.4) 4.9 17.0 13.6 ( 7.0)

7 1.5 ( 0.9) ( 0.5) ( 0.5) ( 0.4) ( 0.3) ( 0.2) ( 0.5) 4.7 (17.0) 14.7 6.6

8 1.4 0.8 ( 0.5) ( 0.5) ( 0.4) ( 0.3) ( 0.2) ( 0.5) 4.3 16.2 13.4 6.1

9 1.3 ( 0.8) ( 0.5) ( 0.5) ( 0.4) ( 0.3) ( 0.2) ( 0.9) 2.0 15.8 16.3 4.7

10 1.2 ( 0.8) ( 0.5) ( 0.5) ( 0.4) ( 0.3) ( 0.2) ( 1.2) 1.4 15.6 21.1 4.2

11 ( 1.2) ( 0.8) ( 0.5) ( 0.4) ( 0.4) ( 0.3) ( 0.2) ( 1.6) 0.9 12.2 14.0 2.9

12 ( 1.2) ( 0.8) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 1.7) 1.4 11.3 14.8 3.3

13 ( 1.2) ( 0.8) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 1.7) 2.9 12.5 17.0 3.6

14 ( 1.2) ( 0.8) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 1.3) 4.0 11.3 15.4 2.6

15 ( 1.2) ( 0.8) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.9) 6.6 11.6 13.9 2.4

16 ( 1.2) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.8) 8.1 14.9 14.4 2.4

17 ( 1.2) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.7) 12.1 17.4 16.4 2.0

18 ( 1.1) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.6) 19.8 17.8 15.9 2.2

19 ( 1.1) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.5) 26.6 17.9 13.4 1.6

20 ( 1.1) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.5) 22.0 17.5 12.1 1.2

21 ( 1.1) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 0.6) 15.3 17.8 11.8 1.1

22 ( 1.1) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) ( 1.0) 14.6 16.1 11.9 0.9

23 ( 1.0) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.1 16.3 16.8 13.0 0.9

24 ( 1.0) ( 0.7) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.9 11.9 16.4 13.3 0.9

25 ( 1.0) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.9 10.3 17.5 13.2 1.0

26 ( 1.0) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.8 7.8 13.7 ( 9.3) 1.0

27 ( 1.0) ( 0.6) ( 0.5) ( 0.4) ( 0.3) 0.3 ( 0.2) 2.3 7.3 13.9 ( 9.3) 0.9

28 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.1 7.1 17.0 ( 8.5) 0.9

29 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.3) ( 0.2) 2.9 4.6 25.9 10.5 0.9

30 ( 0.9) ( 0.6) ( 0.5) ( 0.4) ( 0.3) ( 0.2) 4.2 4.0 41.7 18.2 0.7

31 ( 0.9) ( 0.5) ( 0.4) ( 0.3) 6.3 27.4 16.2

Total (41.7) (22.2) (16.4) (12.8) ( 9.9) ( 9.6) ( 7.4) (45.4) 260.6 498.9 (460.4) (109.4) 1,494.7

Departure from normal 15.2 9.4 6.9 5.3 4.2 4.2 2.4 3.9 -47.9 -200.8 -152.9 -40

Standardized value 0.6 0.7 0.7 0.7 0.7 0.8 0.5 0.1 - 0.2 - 0.3 - 0.2 - 0.3

Total of measured values 19.1 0.0 0.0 0.0 0.0 0.0 0.0 28.4 260.6 481.9 433.3 76.1 1,299.5

Total of estimated values (22.5) (22.2) (16.4) (12.8) ( 9.9) ( 9.6) ( 7.4) (17.0) ( 0.0) (17.0) (27.1) (33.3) (195.2)

Percent measured 46 0 0 0 0 0 0 63 100 97 94 70 87
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0.1

1.0

10.0

100.0

RUNOFF, IN MILLIMETERS PER DAY 

1996 Estimated daily

values

1996 Measured

instantaneous values

1967-96 Measured

instantaneous values

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
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