U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

OPEN-FILE REPORT 03-113Sheet 2

USG

S - UAF/GI - ADG

GS

Ala

ska

Volcano Observatory

Kanag a Volcano is a 1,300 m (4,287-foot) high, historically active cone-shaped stratovolcano located on the north end of Kanaga Island in the Andreanof Islands Group of the Aleutian Islands. The volcano is undissected, symmetrical in profile, and is characterized by blocky andesitic lava flows, with well-developed levees and steep flow fronts, that emanate radially from, or near, the 200-m-wide summit crater. The lack of dissection of the cone suggests the entire edifice was constructed in post-glacial Holocene time. Historical eruptions were reported in 1791, 1827, 1829, 1904-1906, and 1993-95 (Miller and others, 1998); questionable eruptions occurred in 1763, 1768, 1786, 1790, and 1933. The upper flanks of the cone are very steep (>30°) and flows moving down these steep flows commonly fragment into breccias and lahars. A non-vegetated lahar, or group of lahars, extends from high on the southeast flank of the cone down to the northeast shore of the intracaldera lake. This lahar deposit was observed in 1999 but does not appear to be present on aerial photos taken in 1974 and is assumed to be part of the 1994-95 eruption. Most recent eruptions of Kanag a, including the 1994-95 eruption, were primarily effusive in character with a subordinate explosive component. Lava was extruded from, or near, the summit vent and moved down the flank of the cone in some cases reaching the ocean. In 1994, lava flows going down the very steep north and west flanks broke up into incandescent avalanches tumbling over steep truncated sea cliffs into the Bering Sea. A common feature of Kanaga central vent eruptions is the occurrence of widespread ballistics and accompanying craters. Steam and fine ash plumes rose to 7.5 km ASL and drifted a few tens of kilometers downwind. Plumes such as these are unlikely to deposit significant (i.e., sufficiently thick to leave a permanent record) tephras on other islands downwind. Se veral recent non-vegetated flow fields (labeled Qhlf on the geologic map) are identifiable on the east-northeast, south, southwest, west-southwest, and northwest flanks of the volcano with the latter three fields extending to the ocean. Older lava flows and flow fields (labeled Qholf) are vegetated to varying degrees but retain fresh-appearing surface features such as levees, pressure ridges and steep lobate flow fronts. In the past, lava flows from both units may have broken out from points below but near the summit. Pyroclastic flows and pumiceous debris flows along the southern base of the volcano contain abundant silicic pumice clasts. The source domes for this material appear to have been overridden by andesitic flows that form the present-day Kanaga edifice.

Geology of Kanaga Volcano

Kanag a Volcano is composed primarily of porphyritic two-pyroxene andesite; phenocrysts are chiefly plagioclase, clinopyroxene, orthopyroxene, and Fe-oxide minerals with traces of olivine and hornblende. The groundmass is usually a pale to light-brown glass with microlites of plagioclase and pyroxene. Kanaga volcanic rocks are medium-K, calcalkaline in character; samples from the present edifice show a relatively narrow compositional range from 51 to 66 percent SiO2 with an average of 56 percent. Pumices from the p yroclastic flows, airfalls, and debris flows are more silicic ranging from 63 to 66 percent SiO2 (dacitic). Multiple dome collapse is the most likely origin for these deposits and, although dacite domes have not been identified at Kanaga, the location and pumice clast size of the pyroclastic deposits suggests their parent domes are buried by still more recent lava flows from the Kanaga cone. Silicic andesite domes crop out in the southern part of the caldera in and adjacent to the intra-caldera lake. These domes are compositionally different from the silicic pumices and are thought to represent an earlier eruptive phase more closely related to the andesite edifice. Kanag a Volcano is partly surrounded by, and in fault contact with, overlapping volcanic cones. Coats (1955) and Brophy (1990) consider the oldest of these cones to be exposed along the north coast of the island immediately east of Kanaga Volcano. This composite cone consists chiefly of massive, thick-bedded, altered K-rich andesite lava flows and volcanic breccias. The cone is overlain by over 450 m of basaltic andesite and andesite flows and volcanic breccias that form most of Kanaton Ridge. Kanag a Volcano is partly enclosed on its south and east sides by Kanaton Ridge, a prominent scarp-like feature sculpted into the side of a large ancestral basaltic andesite cone named Mt. Kanaton by Coats (1955). This crescent-shaped feature is either the remnant of 1) a typical island-arc collapse caldera-rim now breached to the north, or more likely the 2) the scarp of an avalanche caldera resulting from directed edifice failure to the north and west. Typical Aleutian arc collapse calderas are surrounded by voluminous pyroclastic flow or tephra deposits representing the catastrophic caldera-forming eruption (Miller and Smith, 1987). Pyroclastic flow deposits are uncommon on Kanaga Island south of Kanaton Ridge and tephra deposits, although abundant, do not seem sufficiently thick or coarse enough to represent a caldera-forming eruption and are absent in some areas where deposition would have been expected. The lack of suitable pyroclastic flanking deposits could also be explained if Kanaton

Ridge is a somma-like feature representing an avalanche scarp of northward-directed edifice failure. This failure may or may not have been associated with voluminous explosive volcanic activity and thus could have occurred without leaving voluminous deposits on Kanaga Island itself. These observations could be explained by assuming a Pleistocene age for the formation of Kanaton caldera. Subsequent glaciation could have resulted in the erosion of deposits from the caldera-forming eruption. The thick section of pumice-rich, cross-bedded outwash found in the central part of the island indicates at least some silicic explosive volcanism occurred prior to the Holocene and indeed pumice in the deposit may represent material from a caldera-forming eruption. An intracaldera lak e about 1.5 km long occurs in the southeast corner of the caldera at an elevation of about 330 m (1,000 feet) above sea level. A flat-topped lava dome in the center of the lake and a beveled pumice deposit on the southeast shore of the lake are indicative of higher lake levels in the past. A fan-shaped lahar deposit that contains cobble and small boulder size clasts of pumice and lithics extends from the southwest slope of Kanaga volcano to the ocean and may be evidence of catastrophic release of water from the southwest corner of the caldera through the southwest corner of the caldera, possibly associated with a dome eruption during a higher stand of the lake. The lahar is now separated from the caldera by a young (1906) lava flow. Hot springs are scattered o ver an east-west area of about 100 m x 20 m along the south side of stream about 500 feet above sea level and about 1 km from Weed Bight. Temperatures of up to 92°C were measured in several places but several small (5-10 cm high) geysers were noted in inaccessible locations suggesting higher temperatures; some of these geysers were surrounded by cones of travertine (?) up to 20 cm high and 70 cm wide. Fumarolic activity. Coats (1955), who climbed the volcano in 1946, reported fumaroles near the summit of the volcano on the southeast, south, and southwest sides and several fumaroles in the bottom of the 60 m deep summit crater. Aerial observations in 1999 indicate much the same situation prevailed. Coats (1955) measured temperatures of 104°C at these fumaroles and also noted the presence of sulfur crusts and a faint odor of hydrogen sulfide. Aerial photographs taken in 1974 suggest a fissure striking NE may extend through the summit vent for a few hundred kilometers on either side of the vent. Photographs of the 1994-1955 eruption indicated a "leaky" summit vent with fumarolic activity spread around the outside of the vent; a particularly vigorous vent was noted down the southeast flank several hundred meters from the summit on strike with the apparent summit fissure.

Na 2O

+ K

2O W

EIG

HT

PE

RC

EN

T

SiO2 WEIGHT PERCENT

2

3

4

5

6

7

8

9

10

45 50 55 60 65 70 75

Trachybasalt

Basaltictrachyandesite

Trachyandesite

Trachyte

Rhyolite

DaciteAndesiteBasalticandesite

Basalt

A

Variation diagrams for Kanaga volcanic center rocks. Complete major and minor element data included in Table 1. (A) Total alkali-silica diagram. Discriminant lines from LeBas and others (1986). (B) FeO*/MgO-silica diagram. Tholeiite-calkalkaline discriminant line from Miyashiro (1974).

50 55 60 65 700

1

2

3

4

TH

CA

B

Lava flows, 1994 (Qhlf1994)

Lava flows, 1906 (Qhlf1906)

Lava flows, cone building sequence (Qholf)

Lava domes (Qhld)

Lava flows of Mt. Kanaton (TQKv)

Juvenile pumice in lahar deposits (Qhla)

Pyroclastic-flow deposits (Qhpf)

Pumice from tephra deposit, 1994 eruption

EXPLANATION

FeO

*/M

gO W

EIG

HT

PE

RC

EN

T

SiO2 WEIGHT PERCENT

Map unitLithologySample #SiO2Al2O3FeO*MgOCaONa2OK2OTiO2P2O5MnO

CsRbBaSrLaCePrNdSmEuGdTbDyHoErTmYbLuY ZrHfNbTaPbThUGaCuZnVScCrNi

1994 ashNye 659.9418.525.112.257.204.091.950.630.190.12

Qhlf1994lava flow 0NK07

56.2317.80

7.273.948.633.411.530.850.180.17

2.87 37.40540.00396.00 10.44 22.33 2.9813.86

3.941.184.020.694.350.932.600.392.480.41

24.81115.00

3.252.420.189.283.711.53

20.0076.0071.00

212.0027.0028.0010.00

Qhlf1906 lava flow

0M01A58.1417.28

6.913.477.753.551.750.810.190.16

2.5242.93

603.00396.0011.8024.68

3.2414.82

4.041.213.980.704.250.912.640.382.470.40

24.96131.00

3.492.700.198.934.411.78

19.0055.0067.00

196.0024.4020.00

6.00

Qhlf1906 lava flow

0M09A56.5417.70

7.293.868.413.461.540.850.180.17

2.2136.60

537.00399.0010.5522.43

3.0314.08

3.931.174.110.684.310.942.540.382.510.40

24.35115.00

3.262.410.177.723.511.49

18.0066.0067.00

219.0026.0020.00

6.00

Qhlf1906 lava flow C97

55.1817.97

8.123.959.222.611.501.000.270.17

Qhlf06 lava flow

C11655.6216.88

8.623.798.653.511.640.840.280.17

Qholf lava flow

KG2155.5017.87

7.185.109.073.291.380.79

0.15

36.00444.00370.00

35.0093.00

211.0029.00

Qholf lava flow

C11257.3118.21

7.513.077.883.651.650.080.460.18

Qholf lava flow

C10760.1416.60

6.642.587.243.602.050.720.250.16

Qholf lava flow

KG2254.7818.49

8.054.638.093.581.540.65

0.19

36.00482.00379.00

32.00105.00

232.0026.00

Qholf lava flow

KG2358.8017.48

6.473.327.443.541.820.78

0.16

46.00587.00371.00

36.00122.00

190.0021.00

Oholf lava flow

KG2456.8518.27

7.253.688.333.181.440.85

0.15

37.00487.00394.00

33.0089.00

220.0024.00

Qholf lava flow

KG2555.6017.90

7.454.46

10.002.391.290.70

0.16

33.00381.00335.00

30.0098.00

186.0030.00

Qholf lava flow

0NK0456.0717.55

7.634.008.623.391.510.880.180.17

2.7735.52

527.00398.0010.2621.90

2.9213.60

3.801.183.970.684.270.912.560.382.380.39

23.70114.00

3.152.310.178.833.551.45

19.0079.0071.00

237.0025.8024.00

9.00

Qholf lava flow

00CW241d56.4518.01

7.183.838.543.381.460.800.180.17

2.1636.23

522.00402.0010.1821.81

2.9313.59

3.761.133.830.674.230.902.560.372.430.40

24.24107.00

3.172.310.168.863.681.51

17.00123.00105.00207.0026.8026.0012.00

Qholf lava flow0NK02B1

55.5617.86

7.194.128.873.291.460.860.170.17

2.8336.34

518.00403.0010.0321.52

2.8913.47

3.751.153.950.684.330.902.490.382.420.39

24.62109.00

3.122.310.178.963.561.44

18.0071.0075.00

233.0028.6033.0012.00

Qholf lava flow0NK02L1

58.4417.23

6.913.407.603.581.720.770.190.17

3.2543.35

608.00391.0011.7624.84

3.2815.00

4.061.204.080.704.390.942.700.402.560.41

25.74131.00

3.552.710.19

10.174.291.77

18.0063.0072.00

186.0023.8021.00

7.00

Qholf lava flow0NK02L2

56.3717.70

7.294.039.623.361.470.820.180.17

2.8637.22

529.00397.0010.2922.17

2.9513.66

3.861.163.940.684.280.902.550.382.480.40

24.61114.00

3.182.350.169.523.691.50

21.0069.0075.00

214.0027.2030.0010.00

Qholf lava flow0NK02P1

56.1617.73

7.454.028.673.361.440.820.180.17

2.8737.05

524.00406.0010.2821.95

2.9413.74

3.821.163.950.674.280.902.520.382.460.39

24.52110.00

3.132.310.179.443.611.47

20.0045.0075.00

208.0027.0026.0012.00

Qholf lava flow

0NK0956.4517.98

7.343.758.523.411.420.760.200.18

1.7936.72

564.00424.0010.6722.37

2.9513.43

3.731.183.680.623.940.842.360.352.230.37

22.27105.00

2.872.330.168.603.971.64

18.0048.0072.00

204.0024.4022.0012.00

Qholf pumice

0M09B55.7618.10

7.334.088.783.351.440.820.170.16

2.08834.702

504394

9.90221.1932.855

13.1513.82

1.1423.9440.6574.2720.8772.5320.3732.3940.389

24.045106

3.122.270.177.623.331.37

209580

23026.6

2411

Qholf pumice

0M09C57.8917.44

7.013.587.723.541.660.790.190.17

2.50140.655

583383

11.28323.8473.184

14.4144.0371.1744.0280.6874.3870.9082.5770.3862.5550.409

24.718123

3.522.560.19

9.34

1.66184972

19522.2

239

Qholf pumice

0M1058.6217.42

6.753.317.453.621.730.760.190.16

2.67643.377

615381

12.00525.067

3.3115.1554.1451.2074.2580.6924.3160.9242.6310.3952.5310.421

25.329127

3.612.730.199.454.281.77

198587

18121.4

126

Qholf pumice

00NK01P156.8117.76

7.193.808.403.381.520.800.190.17

2.88337.57

537400

10.522.4493.008

13.8863.89

1.1543.9140.6764.2760.8812.5030.3832.4610.404

24.394117

3.222.380.179.733.721.51

176872

19525.7

288

Qholfpumice

00CW08-157.6717.56

7.173.347.783.581.720.790.220.17

2.54343.296

636431

12.67426.7713.541

16.0234.2681.2774.1930.7144.4150.916

2.610.3912.5390.419

25.3131283.6

2.750.198.974.491.82

197477

20321.7

114

Qholf pumice

00CW241b57.1517.77

7.183.678.193.371.530.790.180.17

2.28938.017

548411

10.69622.7593.036

14.2263.8421.2023.9410.6964.3410.9122.592

0.392.504

0.4124.924

1113.3

2.430.188.8

3.881.59

197792

2002619

9

Qholf pumice

00CW241c59.0517.51

6.523.257.283.491.750.780.200.17

2.59342.537

606389

11.7224.688

3.2814.9814.0171.1813.8860.6864.3510.9252.6260.386

2.540.417

24.5361243.512.610.199.934.371.79

206780

17921.6

167

Qhld andesite

0NK0360.4317.39

6.202.876.893.671.540.640.210.18

3.18639.872

601412

11.26723.5923.045

13.6313.5711.1363.4910.6013.7760.8222.319

0.352.308

0.3822.157

1203.182.490.18

10.384.181.71

192777

14317.8

155

Qhld andesite

0NK0557.5717.88

7.103.708.073.351.280.690.200.18

2.6933.218

503386

10.08420.9792.812

12.8373.5271.1663.5710.6113.8380.8262.3360.3572.2540.376

21.9361012.812.110.157.593.361.38

163778

16821.8

329

Qhldandesite

0NK0654.4717.56

7.505.189.693.131.350.810.160.16

2.57132.139

467382

9.07719.548

2.612.2913.4891.0673.635

0.63.8680.829

2.30.35

2.1410.358

21.9771052.822.110.158.333.161.31

176266

22433.510730

TQkv lava flow

00CW24-358.8017.68

6.613.127.573.551.660.670.180.16

0.98944.472

649414

11.37522.9932.907

12.8363.2771.0663.1460.5233.3320.7262.0040.3052.0270.326

19.41072.952.440.198.395.142.06

183666

17321.5

196

TQkv lava flow

C13551.7218.66

9.114.619.153.671.850.720.320.18

TQkv lava flow

C12753.6517.68

8.135.518.393.381.710.680.420.18

TQkv lava flow

C124 60.4916.84

6.543.126.313.622.050.480.380.16

TQkv lava flow

KG1858.4817.87

7.423.137.113.491.840.64

0.16

23608

113

TQkv lava flow

0M01C60.0916.96

6.393.006.823.711.920.740.190.16

2.84847.59

657385

12.60226.4283.447

15.5254.0841.2094.059

0.694.3380.9412.6650.4032.6350.432

26.0051433.822.930.229.984.91

2195976

17621.6

95

TQkv lava flow

0NK0857.3617.46

7.063.608.213.621.550.770.200.17

2.83738.646

586456

11.68324.215

3.1414.2693.8341.1763.7790.6273.916

0.842.36

0.3522.2340.369

22.3781133.162.470.188.623.931.61

204369

21121.7

229

TQkv lava flow

00CW20-159.5317.67

6.692.686.523.802.060.660.230.15

2.20152.093

783493

15.45929.1434.093

18.2634.5891.2994.3080.7054.3750.9312.5910.3932.5540.42725.64

1273.722.890.21

10.695.812.44

204274

16215.1

147

Map unitLithologySample #SiO2Al2O3FeO*MgOCaONa2OK2OTiO2P2O5MnO

CsRbBaSrLaCePrNdSmEuGdTbDyHoErTmYbLuY ZrHfNbTaPbThUGaCuZnVScCrNi

TQkv lava flow

9M12058.4917.78

6.433.357.773.561.620.670.170.17

1.10141.593

651447

9.98320.1872.57911.543.045

1.012.9990.5043.3360.6831.9660.2991.9670.319

18.50598

2.822.310.175.754.131.72

183061

20023.2

266

TQkv lava flow

KG3257.5418.56

6.923.427.453.871.830.73

0.16

44586424

35107

TQkv lava flow

KG3156.8518.56

7.153.387.563.951.840.53

0.17

40355424

22110

TQkv lava flow

KG1957.6218.30

6.843.337.593.701.790.68

0.14

42686491

33102

TQkv lava flow

KG1258.3318.22

6.703.096.924.021.900.67

0.16

44709484

35117

TQkv lava flow

KG1858.8317.98

6.753.157.153.511.850.64

0.16

46608459

36113

TQkv lava flow

KG1759.1417.88

6.682.866.883.472.270.68

0.14

56736469

35117

TQkv lava flow

KG1658.0218.22

6.693.117.503.592.000.69

0.16

37651494

35101

TQkv lava flow

KG1558.4917.94

6.723.057.073.662.240.68

0.15

53754471

35122

TQkv lava flow

KG1457.4717.99

7.173.217.623.741.980.66

0.17

50708498

34113

TQkv lava flow

KG1360.0718.31

6.522.926.833.982.360.71

0.14

61750420

35147

TQkv lava flow

KG3658.0318.02

6.753.217.213.812.100.70

0.16

57760463

35114

TQkv lava flow

KG3557.2518.47

7.243.167.613.641.850.62

0.16

42690499

35101

TQkv lava flow

KG3459.6417.89

6.052.696.643.992.300.66

0.14

58864463

34134

TQkv lava flow

KG3359.5918.06

6.222.816.303.982.220.65

0.16

51797445

33144

TQkv lava flow

KG3857.57

18.66.733.027.013.782.600.71

0.16

68756427

39173

TQkv lava flow

KG3958.2418.46

6.402.816.913.852.600.67

0.16

66758427

37178

TQkv lava flow

KG4056.6318.50

7.213.237.663.642.250.71

0.16

61675451

36153

TQkv lava flow

KG4157.9618.33

6.722.897.403.572.260.70

0.16

633752431

39176

TQkv lava flow

KG4259.15

17.96.642.906.883.772.210.71

0.17

56672379

34143

TQkv lava flow

KG4360.2817.84

6.032.865.783.902.490.67

0.15

56708367

39155

TQkv lava flow

KG4561.6818.56

4.701.836.153.852.470.64

0.11

61728411

62159

TQkv lava flow

9M2257.8318.33

6.672.747.113.782.410.720.240.17

1.65464.748

785459

15.71933.2454.327

19.4214.9341.347

4.560.7414.7270.9992.8480.4172.794

0.4426.725

1504.663.870.28

10.597.323.07

205176

17117.2

97

Qhla pumice00CW241e

65.6516.62

4.261.605.034.181.910.450.160.14

1.81651.937

734393

13.06825.494

3.1313.0863.1831.008

2.960.5063.1920.6831.9670.3112.1190.365

19.133137

3.752.820.218.165.352.15

171357879.9

23

Qhla pumice

0M01B63.6316.87

4.932.085.623.882.150.520.190.15

1.95360.669

861420

13.77827.054

3.2513.843.3511.0343.0540.5083.1580.6781.9290.2941.9790.331

18.8561333.552.940.227.076.752.68

195465

10312.9

84

Qhpf pumice

0M08A66.3616.65

3.911.514.814.121.900.430.160.15

3.01149.696

721364

13.46526.1553.193

13.4143.161

0.932.9230.4933.1710.6581.8980.314

2.130.36

18.5021473.792.740.229.565.112.07

182771747.5

12

Qhpf pumice00CW083

66.2116.63

3.961.554.854.151.910.430.160.15

3.03950.704

718382

13.68126.8853.251

13.7053.2110.9983.014

0.523.2930.6992.0530.3272.128

0.3719.44

1403.872.790.22

10.155.3

2.1917

964698.5

12

Qhpf pumice00CW14-2

66.3016.53

4.091.434.904.101.910.430.160.15

3.04850.476

721375

13.36826.2263.168

13.4953.2420.9562.9630.502

3.220.6781.983

0.312.1250.365

19.2531443.762.770.22

10.055.342.15

174079768.7

12

Qhtc pumice

C13063.9216.85

5.032.514.923.901.690.690.320.17

TABLE 1.--CHEMICAL ANALYSES OF LAVA AND PYROCLASTS FROM KANAGA VOLCANO[Analyses with sample numbers prefixed by 9, 0, or 00 by Geoanalytical Laboratory,Washington State University.

All other analyses from Coats, 1952, and Brophy, 1990]

Brophy, J.G., 1990, Andesites from northeastern Kanaga Island, Aleutians-implications for calc- alkaline fractionation mechanisms and magma chamber development: Contributions to Mineralogy and Petrology, vol. 104, no. 5, p. 568-581.

Coats, R.R., 1952, Magmatic differentiation in Tertiary and Quaternary volcanic rocks from Adak and Kanaga Islands, Aleutian Islands, Alaska: Geological Society of America Bulletin, vol. 63, no. 5, p. 485-514.

Coats, R.R., 1956, Geology of northern Kanaga Island, Alaska: U.S. Geological Survey Bulletin 1028-D. Le Bas, M .J., Le Maitre, R. W., Streckeisen, A., and Zanettin, B. A., 1986, Chemical classification of volcanic rocks based on the total alkali-silica diagram: Journal of Petrology, vol. 27, no. 3, p.745-750. Miller, T.P., and Smith, R.L., 1987, Late Quaternary caldera-forming eruptions in the eastern Aleutian arc, Alaska: Geology, vol. 15, p. 434-438.

Miller, T.P., McGimsey, R.G., Richter, D.H., Riehle, J.R., Nye, C.J., Yount, M.E., and Dumoulin, J.A., 1998, Catalog of the historically active volcanoes of Alaska: U.S. Geological Survey Open-File Report 98-582, 104 p.

Miyashiro, A., 1974, Volcanic rock series in island arcs and active continental margins: American Journal of Science, vol. 274, no. 4, p. 321-355.

REFERENCES CITED

Kanaga Volcano, July 2000, view is to the southeast. Selected geologic units indicated by map symbols.Photograph by C.J. Nye, Alaska Division of Geological and Geophysical Surveys.

Qhlf94Qhlf94

Qhlf94

Qholf

Kanaton Ridge

Qholf

Kanaga Volcano, July 2000, view is to the east across intracaldera lake. Selected geologic units indicatedby map symbols. Photograph by C.F. Waythomas, U.S. Geological Survey.

Qhlf06

Qld

Qhpf

Kanaton Ridge