REPORT ON THE 1997 ACTIVITY OF

SHRUB MUD VOLCANO, 

WRANGELL-ST. ELIAS NATIONAL PARK

AND PRESERVE, 

SOUTH CENTRAL ALASKA

U.S. GEOLOGICAL SURVEY OPEN-RLE REPORT 98-128
U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

REPORT ON THE 1997 ACTIVITY OF SHRUB MUD VOLCANO,

WRANGELL-ST. ELIAS NATIONAL PARK AND PRESERVE,

SOUTHCENTRAL ALASKA

by

10 "3 Donald H. Richter , Robert B. Symonds , Danny S. Rosenkrans , 

Robert G. McGimsey1 , William C. Evans4, and Robert J. Poreda5

!U.S. Geological Survey, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK 99508

2U.S. Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661

3Wrangell-St Elias National Park and Preserve, P.O. Box 439, Copper Center, AK 99573

4U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025

5Dept. of Earth and Environmental Science, 227 Hutchison Hall, University of Rochester, Rochester, NY 14627

Open-file Report 98-128

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or 

firm names is for descriptive purposes only and does not imply endorsement by the U.S. 

Government.

1998
CONTENTS

ABSTRACT

INTRODUCTION

GEOLOGIC SETTING AND HISTORICAL ACTIVITY

1997 ACTIVITY

GAS SAMPLING AND ANALYTICAL METHODS

ANALYTICAL RESULTS

CONCLUSIONS

Page

4

4

4

REFERENCES

TABLE 1.

COVERPHOTO.

Figure 1.

Figure 2.

Figure 3.

TABLES 

Chemical composition of gases from Shrub mud volcano

FIGURES

Oblique aerial view of Shrub mud volcano from the southwest 

on 30 June 1997, showing mud stream descending flank from the 

gusher vents.

Index map of Glennallen, Alaska, showing location of the Klawasi 

group of mud volcanoes.

Sketch map of Shrub mud volcano showing vents and mud 

deposits as of 21 and 30 June 1997. 

Sketch map of Shrub mud volcano showing vents and mud 

deposits as of 13 August 1997.
ABSTRACT

Shrub mud volcano, one of three in the Klawasi group in the Copper River Basin, Alaska, 

was reported to be erupting warm mud and CC^-rich gas in the spring of 1997. Three on-site 

investigations of the renewed activity were made on 21 and 30 June and on 13 August 1997. The 

current activity is much more vigorous and the erupted products hotter (up to 46°C) than has 

been observed previously at the Klawasi group of mud volcanoes. The mud and gas erupt from 

several circular depressions and fissure vents on the mud volcano. Activity ranges from quiet 

effusion of bubbling mud to violent discharge of mud and gas, which sends mud up to 10m 

above the vents. The gas discharges contain over 98% CO2 and minor to trace amounts of 

meteoric gases (N2, C>2, Ar), CHU, and He. Carbon isotope data suggest that the COz comes from 

a mixture of magmatic CO2 and CO2 from contact metamorphism of underlying limestone. 

Isotopic data also confirm that He in these gases derives from magmatic and crustal sources. The 

CO2 in the discharged gases is killing animals, birds, and trees in the vicinity of the mud volcano 

and poses a life-threatening hazard to human visitors.

INTRODUCTION

Shrub mud volcano, in the Copper River Basin, approximately 27 km east of Glennallen, 

Alaska (Figures 1 and 2), began to vigorously erupt potentially dangerous CO2-rich gas and 

warm saline mud in the spring of 1997. This activity may have begun, on a smaller scale, in 

1996 according to prevously unreported observations. The 1997 activity was first noticed by 

Alaska Department of Fish and Game personnel on 12 June 1997. Since then, the activity has 

been monitored by the U.S. Geological Survey and the National Park Service. On site 

investigations were conducted on 21 and 30 June (Figure 3) and on 13 August 1997 (Figure 4), 

and an aerial inspection was made on 2 December 1997. During the investigation on 30 June 

1997, we collected gases from one of the vents. Although the eruption poses no hazard to 

Glennallen or other communities in the Copper River Basin, the gas does pose a potential hazard 

for human visits to the mud volcano. This report describes our 1997 observations and also 

documents some preliminary analytical results on our gas samples.

GEOLOGIC SETTING AND HISTORICAL ACTIVITY

Shrub is one of three large mud volcanoes in the Copper River Basin near the west slope 

of Mt. Drum, a large Pleistocene volcano that was last active about 240,000 years ago (Richter 

and others, 1994). These mud volcanoes, called the Klawasi group, are elevated some 50-100 m 

above the surrounding terrain and are constructed entirely of material derived from the 

underlying glaciolacustrine deposits of the Basin (Figure 2). Shrub has apparently been virtually 

inactive for many years. Minor activity was observed in the mid-1950's, but since then the mud 

volcano was probably quiet until the summer of 1996 when vigorous activity was observed. The 

other 2 mud volcanoes of the group, Upper and Lower Klawasi mud volcanoes (Figure 1), have 

been active throughout this period and have provided temperature and chemical data on the mud 

and gas discharges (Nichols and Yehle, 1961; Grantz and others, 1962; Motyka and others, 

1989). These investigations show that the Klawasi mud volcanoes erupt 20-25°C mud mixed 

with Ca-poor, Na-HCOs-rich saline water and CO2-rich gas. Motyka and others (1989) suggest
that the warm saline water is connate in origin and that the COi derives from degassing of deepseated magma and contact decarbonation of underlying Mesozoic limestone beds.

The first known description of Shrub and its activity was presented by Nichols and Yehle 

(1961) who visited the mud volcano in 1955 and 1956. In 1955 a vegetation-bare depression, 

about 35 m in diameter, was present on the southwest side of the cone about 10m below the 

summit. The depression contained 7 small pools, 5-45 cm in diameter, from which issued minor 

mud and gas. By 1956, only 4 pools, 2-5 cm in diameter, remained and both mud and gas 

discharges were reduced. This depression was apparently located in the area now occupied by 

the very active gusher vents (Figures 3 and 4). In August 1991 a brief examination of the mud 

volcano by one of us (DSR) revealed no activity, nor was there indication of any recent activity.

No other descriptions of Shrub mud volcano or reports of activity are known until the 

summer of 1996 when a helicopter pilot observed an active mud spring low on the north flank of 

the cone (Figure 3) and probably activity from the summit area near the present fissure vent 

(Fritz Wohlwend, Trans-Alaska Helicopters, Inc., Personal communication 1997). This activity 

was never reported publicly, but fortuitously we flew with this pilot on our first visit to the mud 

volcano on 21 June 1997.

ACTIVITY

The present ongoing activity at Shrub is much more vigorous, and the temperatures 

higher, than what has been observed in the past at the nearby Klawasi mud volcanoes. During 

the visit of 21 June we examined all known sites where mud or gas was discharging as well as a 

vent area for the 1996 activity (Figure 3). The most active area was immediately below 

(southeast of) the cone's summit where a 65-m-long east-trending fissure was discharging 

copious amounts of mud and gas at 43°C. Recently dead spruce trees on the slopes below this 

fissure suggest the area was also the site of summit activity in 1996. Mud and gas production 

was also vigorous at a central vent, about 1 m in diameter, within a group of three vents, about 

100 m west of the fissure vent. The two other vents in this latter group were less active. 

Approximately a third of the way down from the summit on the north side of the cone, in dense 

alder-willow-birch growth, a 4- to 6-m-diameter pit, 1- to 2-m-deep, was filled with very active 

bubbling mud. Although the pit had not discharged mud, leaves of alder and birch downslope 

from the pit were browned to heights as much as 2 m above the ground surface suggesting that 

significant amounts of COi-rich gas may have flowed out of the pit prior to our visit. We did 

observe a dense layer of condensate (probably water mixed withCO2) up to about a meter above 

the roiling mud surface. Northwest of this gas/mud pit and lower on the cone's flank a number 

of small vents were quietly discharging mud, with no apparent gas, through a thick surficial 

organic mat. Mud discharging from the largest of these vents had a temperature of 47°C, the 

hottest recorded on the mud volcano.

On 30 June we revisited Shrub to sample gases from the west end of the summit fissure. 

The fissure was still active but activity was restricted to a deep (about 3-5 m) pit in the middle of 

the fissure; temperatures remained at 43°C. The northernmost of the gushing vents was very 

active, noisily producing large bubbles of mud as much as 2 m in diameter that burst as high as 

10m above the vent. There was minor mud emission from the central vent and the southernmost 

vent was inactive. The mud/gas pit on the north flank was not visited, but we could see from the 

air that it was still active.
A month and a half later on 13 August numerous changes in activity were observed, 

although vigorous mud and gas emission continued (Figure 4). The fissure vent was virtually 

inactive. In the deeper parts of the fissure some roily mud was present but none was reaching the 

surface. About 50 m south of the fissure a small pit (vent) was discharging a thin trickle of mud. 

At the gushing vents the former weakly active vent was now the major producer of mud and gas. 

The temperature was 46°C, ~3°C higher than measured on 21 June, and it was estimated that mud 

production was on the order of a cubic meter a minute. The formerly very active vent to the 

north was discharging some mud and a fourth probably new vent a few meters farther to the 

north was also active. The mud/gas pit lower on the north flank was also inactive, but about 10 

m upslope from the pit was a new 3-m-wide collapse pit, at least 5 m deep, which appeared to 

have active mud at the bottom. At the mud vents lower down the flank of the cone it appeared 

that mud emission had decreased, but there were so many small vents, all hidden in the dense 

vegetation, that it was difficult to tell where and how much mud was being discharged. Between 

the 30 June and 13 August site visits there had been significant mud production from these lower 

vents as indicated by the covering of additional 1996 mud during this time frame. A temperature 

of 44°C was slightly lower than what was measured on 30 June.

A low-level flight over the mud volcano on 2 December 1997 revealed that activity 

continued at about the same level as observed in August. At the original mud /gas pit on the 

north flank of the cone, which was quiet on August 13, a small stream of mud was observed 

issuing from the pit and running down the cone. At the gusher vents it appeared a depression 

was forming, maybe similar to the basinal feature observed by Nichols and Yehle (1961) in 

1955-56.

GAS SAMPLING AND ANALYTICAL METHODS

Gas samples were collected from the west end of the summit fissure on 30 June following 

the procedures of Fahlquist and Janik (1992). A 15-cm runnel was held over the surface of the 

bubbling mud. This runnel was attached to a short-length of Tygon tubing that led to an 

evacuated double-port sampling bottle. After purging air from the sampling line with a hand 

pump attached to the outlet port, we clamped the outlet and opened the bottle's inlet valve. At 

this site we filled one evacuated flask for analysis of bulk-gas composition and 513C in CO2, and 

an additional flask for determining rare-gas isotopes. The rare-gas isotope flask was made of 

Corning-1720 glass and fitted with a high-vacuum stopcock to prevent leakage of He. We also 

collected two evacuated bottles partly filled with a known volume of 4N NaOH solution for 

additional determination of the bulk gas composition. These NaOH-collected samples allow 

lower detection limits on some of the less abundant species (e.g., H2 and CO) and are currently 

awaiting analysis by the U.S. Geological Survey (Menlo Park, CA).

One of the NaOH-free evacuated-bottle samples was analyzed using gas chromatograph 

for CO2, N2, O2, CH4, Ar, He, H2S, H2, C2H6, and CO. This sample was also analyzed for 513C 

in CO2 using a Finnigan MAT 251 after the sample was purified using liquid nitrogen traps on a 

high-vacuum line.

The helium isotope sample was analyzed using methods described elsewhere (Poreda and 

others, 1992; Poreda and Parley, 1992). The gases in the flasks were extracted on a high vacuum 

line constructed of stainless steel and Corning-1724 glass. After removal of H2O vapor and CO2
at -90°C and -195°C, respectively, the non-condensable gases (He, Ne, Ar, N2, CH4) were

concentrated using a Toepler pump in series with a Hg-diffusion pump. The amount of noncondensable gas was measured using a calibrated gas splitter fitted with a capacitance 

manometer. Gas ratios (N2, Ar, CHLj.) were analyzed on a Dycor Quadrupole mass spectrometer

fitted with a variable leak valve. The results are combined with the capacitance manometer 

measurement to obtain gas concentrations. Prior to isotope analyses, N2 and O2 were removed

by reaction with Zr-Al alloy (SAES-ST707), and Ar and Ne were adsorbed on activated charcoal 

at 77 K and at 40 K, respectively. Helium isotope ratios and concentrations were then analyzed 

on a VG 5400 Rare Gas Mass Spectrometer fitted with a Faraday cup and a Johnston electron 

multiplier. The Mass Spectrometer was also used to measure concentrations of argon, neon, and 

krypton isotopes. The 2c errors in the ^He/^He ratios are ±0.3% for the reported helium isotope 

value.

ANALYTICAL RESULTS

Table 1 shows the chemical and isotopic analyses of the two evacuated-bottle samples 

collected on 30 June 1997. The chemical analysis is reported (in mol%) as a dry gas 

composition. The results show the sample contains over 98% CO2 with minor to trace amounts 

of N2, O2, CHU, Ar, and He. H2, C2H6, H2S, and CO are below detection. The amount of H2O in 

the sample is necessarily small because the vapor pressure of water at sea level is only 0.018 atm 

for the collection temperature of 16°C.

Ratios of N2/Ar (58.0) and N2/(O2+Ar) (2.02) are close to the mixing line between air 

(N2/Ar = 83.6, N2/(O2+Ar)=3.57) and air-saturated water (N2/Ar = 38.3, N2/(O2+Ar) = 1.78). 

This suggests that N2, O2 , and Ar in this sample come from a meteoric source. After removing 

these shallow meteoric components and discounting any unanalyzed H2O, the renormalized 

composition contains 99.97% CO2, 0.0313% CHi, and 0.0004% He, which we take as the gas 

composition from depth.

The bulk gas composition of the 1997 Shrub gases (Table 1) is very similar to past 

analyses from Upper and Lower Klawasi mud volcanoes (e.g., up to 99% CO2 ; Reitsema, 1979; 

Motyka and others, 1989), suggesting the 1997 Shrub mud volcano gases come from the same 

origin. This is confirmed by the 513C in C02 and 3He/4He data (Table 1), which lie within the 

range of previous analyses of the Upper and Lower Klawasi gases (513C in CO2 = -4.1 to -8.1%o, 

^e/^He = 2.6 - 4.1 R</Ra; Reitsema, 1979; Motyka and others, 1989). The 613C in CO2 data 

supports the interpretation of Motyka and others (1989) that CO2 from the Klawasi group of mud 

volcanoes is a mixture of magmatic CO2 (513C = -5 to -8%o; Allard, 1983) and CO2 derived from 

contact metamorphism of local carbonates (513C = +2.3 - +2.9%o for Chitistone Limestone; 

Reitsema, 1979). As suggested by Motyka and others (1989), the 3He/4He data suggest that He 

derives from a mixture of mantle (8 Ra) and crustal (0.02 Ra) sources.

CONCLUSIONS

Although the renewed activity at Shrub mud volcano is not considered to be a precursor 

to a magmatic volcanic eruption, the discharge of copious amounts of CO2 does present a local 

life-threatening hazard. Numerous dead snowshoe hares and song birds have been observed near
the gas-emitting collapse pits, and more birds and animals are undoubtedly now buried by mud at 

other vents. CC>2 is an odorless and colorless gas that does pose a serious hazard to humans. 

Breathing air with >30% CO2 causes rapid unconsciousness and, if sustained for several minutes, 

death in humans (Stupfel and Le Guern, 1989). Normally CC>2 dissipates rapidly when 

discharged into the atmosphere. But the occasional presence of dead animals and birds, and 

brown vegetation around some of Shrub's vents demonstrates that concentrated streams of CO2 

are occasionally discharged from Shrub. These CO2 streams would obviously be very dangerous 

or fatal to humans, because they can discharge without warning and are invisible. Another 

hazard for humans exists when CC>2, which is heavier than air, concentrates in depressions, snow, 

or manmade structures. Entering natural depressions, digging snow pits, or tent camping on or 

near Shrub could be dangerous. Thus, we discourage visits to the mud volcano while it is in this 

potentially dangerous, active phase. The U.S. Geological Survey and the National Park Service 

will continue to monitor the activity.

REFERENCES

Allard, P., 1983, The origin of hydrogen, carbon, sulfur, nitrogen, and rare gases in volcanic

exhalations: evidence from isotope geochemistry, in Tazieff, H., and Sabroux, J. C., eds., 

Forecasting Volcanic Events: Amsterdam, Elsevier, p. 337-386.

Fahlquist, L., and Janik, C. J., 1992, Procedures for collecting and analyzing gas samples from 

geothermal systems: U.S. Geological Survey Open-File Report 92-211,19 p.

Grantz, Arthur, White, D.E., Whitehead, H.C., and Tagg, A.R., 1962, Saline springs, Copper 

River Lowland, Alaska: American Association of Petroleum Geologists Bull. v. 46, no. 

Il,p.l990-2002.

Motyka, R.J., Poreda, R.J., and Jeffrey, A.W.A., 1989, Geochemistry, isotopic composition, and 

origin of fluids emanating from mud volcanoes in the Copper River basin, Alaska: 

Geochimica et Cosmochimica Acta, v. 53, p. 29-41.

Nichols, D.R. and Yehle, L.A., 1961, Mud volcanoes in the Copper River Basin, Alaska, in

Raasch, G.O., ed., Geology of the Arctic: International Symposium on Arctic Geology, 

1st, Calgary, 1960, Proceedings, v. 2, p. 1063-1087.

Poreda, R. J., and Farley, K. A., 1992, Rare gases in Samoan xenoliths: Earth and Planetary 

Science Letters, v. 113, p. 129-144.

Poreda, R. J., Craig, H., Arnorsson, S., and Welhan, J. A., 1992, Helium isotopes in Icelandic 

geothermal systems: 1. 3He, gas chemistry, and 13C relations: Geochimica et 

Cosmochimica Acta, v. 56, p. 4221-4228.
Reitsema, R. H., 1979, Gases of mud volcanoes in the Copper River Basin, Alaska. Geochimica 

et Cosmochimica Acta, v. 43, p. 183-187.

Richter, D.H., Moll-Stalcup, E.J., Miller, T.P., Lanphere, M.A., Dalrymple, G.B., and Smith,

R.L., 1994, Eruptive history and petrology of Mount Drum volcano, Wrangell Mountains, 

Alaska: Bulletin of Volcanology, v. 56, p.29-46.

Stupfel, M., and Le Guern, F., 1989, Are there biomedical criteria to assess an acute carbon 

dioxide intoxication by a volcanic emission?: Journal of Volcanology and Geothermal 

Research, v. 39, p. 247-264.
Table 1 - Chemical compositions 

of gases from Shrub mud volcano. 

Field numbers: 970630-2 

Location: west end of Fissure

vent

Date: June 30, 1997 

T°C _______________ 16 _____

Chemical Species of Dry Gas (mol%)

CDs

N2

02

CH^

AT

He

CO

H2S

H2

C2H<5

98.3546

1.0613

0.5069

0.0308

0.0183

0.0004

O.001

O.0005

<0.0002

<0.0002

Selected ratios

N2/Ar 58.0 

N2/(O2+Ar) ___________ 2.02 

__________ Isotopic Composition ____

5l3CmCO2 (%0 PBD) ______ -4.64

3He/He (R</R.)T ________ 3.54

R«/R« is ratio of JHe/*He in the sample (corrected 

for air contamination) divided by the same ratio in

10
MUD 

VOLCANOES

Glennallen

Glen Hwy

145°00' 

I

Lower 

Klawasi

Shrub

Upper 

Klawasi Mt. Drum

62°00'

Copper 

Center 0

0

5 

i

5

i 

10

10 

i

i 

15

15 MILES 

I

I

20 KILOMETERS

Figure 1. Index map of the Glennallen, Alaska area showing location of Shrub and Klawasi mud 

volcanoes.

11
/

SHRUB 

MUD VOLCANO

6-21,30-97

-- 

: *-------+ ±

w&

r*

Numerous 

Small Mud Vents

47°C 6/21/97 

46°C 6/30/97

Area of CO2 

Affected Vegetation

2943 \

) Fissure Vent *=^b

10

43°C 6/21/97 

6/30/97

6/21/97 V *-->: 

Stream muddy all the way -' 

to Copper River, about 15 miles

C 

Inactive 6/30/97_-/---------------~-> 

iusher 

Verjts

*----

11

Section 

Corner

0

1 

0

500 1000 i

i

100

i

i i

200 300

I

400

1500 FEET i

J

500 METERS

Contour Interval 1 00 ft

Base from U.S. Geological Survey Gulkana A-3 Quadrangle, Alaska. Graphics by K.Wallace

Figure 3. Sketch map of Shrub mud volcano showing vents and extent of mud deposits as of June 21 and 30, 1997.

12
r-~-

erf*/

SHRUB 

MUD VOLCANO

8-13-97

A 996 Mud

/:::::::::::::::i::^

^^Z^

V^x>>x« v^-------------i

/^xxxx^i

*^ 

^rnall Mud Vfents

Area of CO2 ^ 

Affected Vegetation

Numerou

L::»

Mild/Gas Pit 

^New Pit

6/7J/97

Stream muddy all the way

to Copper River, about 15 miles

10

-If Very Active

-, 46.4°C ,

Gusher

11

Section 

Corner

0

\ 

0

500 1000 ] i

i i t 

100 200 300

Contour Interval 100 ft

400

1500 FEET }

I 

500 METERS

Base from U.S. Geological Survey Gulkana A-3 Quadrangle, Alaska. Graphics by K. Wallace

Figure 4. Sketch map of Shrub mud volcano showing vents and extent of mud deposits as of August 13,1997.

13