Geology of Kanaga Volcano Kanag a Volcano is composed ...The upper flanks of the cone are very steep...
Transcript of Geology of Kanaga Volcano Kanag a Volcano is composed ...The upper flanks of the cone are very steep...
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