2006-2007 eruptions of bezymianny volcano, kamchatka: petrological snapshots of the compositionally...

2006-2007 eruptions of Bezymianny 2006-2007 eruptions of Bezymianny volcano, Kamchatka: Petrological volcano, Kamchatka: Petrological snapshots of the compositionally snapshots of the compositionally

changing magma systemchanging magma system

Pavel IzbekovPavel IzbekovAlaska Volcano Observatory, Geophysical Institute,Alaska Volcano Observatory, Geophysical Institute,

University of Alaska FairbanksUniversity of Alaska Fairbanks

and PIRE team (http://www.gps.alaska.edu/PIRE)and PIRE team (http://www.gps.alaska.edu/PIRE)

December 11, 2007

IntroductionIntroductionVolcanoes, which erupt frequently / continuously, are perfect Volcanoes, which erupt frequently / continuously, are perfect targets to study processes in active magma systems.targets to study processes in active magma systems.

Each individual eruption is a snapshot of magma system at a Each individual eruption is a snapshot of magma system at a particular time.particular time.

The sequence of such snapshots show compositional changes The sequence of such snapshots show compositional changes in magma system as a function of time throughout the entire in magma system as a function of time throughout the entire period of eruptive activity.period of eruptive activity.

By looking at changes of magma composition we might be able By looking at changes of magma composition we might be able to answerto answer

• What processes are behind compositional variations?What processes are behind compositional variations?

• How composition of magma affects eruptive behavior?How composition of magma affects eruptive behavior?

• How fast minerals crystallize in a particular magma How fast minerals crystallize in a particular magma system?system?

Geological background and eruptive historyGeological background and eruptive history

RUSSIARUSSIA

ALASKAALASKA

BezymiannyBezymianny


150 km

SRTM shaded relief DEM, NASASRTM shaded relief DEM, NASA

150 km


150 km150 km


Bezymianny volcano is part of the Bezymianny volcano is part of the Kluchevskoy group of volcanoes, Kluchevskoy group of volcanoes, located in the Northern part of the located in the Northern part of the Central Kamchatkan DepressionCentral Kamchatkan Depression

ShiveluchShiveluch

UshkovskyUshkovskyKluchevskoyKluchevskoy

KamenKamenBezymiannyBezymianny

TolbachikTolbachik

View to the North from the Int. Space Station, NASAView to the North from the Int. Space Station, NASA


Years BCYears BC Years ADYears AD

-8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000

• The oldest part of the stratovolcano was built by lavas, pyroclastic flows, and ash-fall deposits from 10,000-11,000 yr. BP to ca. 6,900 yr. BP.

• The activity resumed at the same location in 4,700 yr. BP. Since then, the stratocone of the modern Bezymianny was built by intermittent eruptive activity, separated by long periods of dormancy (Braitseva et. al., 1991).

• The most recent eruptive cycle of Bezymianny started in October 1955 after ca. 1000 years of quiescence.

Post-1956 trend in eruptive stylePost-1956 trend in eruptive style

2006200619571957

1957 photo by Gorshkov1957 photo by Gorshkov

1946 photo by Piip1946 photo by Piip

19461946

Almost continuous extrusion of lava dome with intermittent low-level explosions

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Time, calendar years

Sporadic energetic explosions, followed by effusive activity.

Bezymianny dome in August 2007Bezymianny dome in August 2007

Trend in whole rock compositionTrend in whole rock composition

54

55

56

57

58

59

60

61

62

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Time of eruption, calendar years

SiO

2, w

t. %


2

2.5

3

3.5

4

4.5

5

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


MgO

, w

t. %


5.5

6

6.5

7

7.5

8

8.5

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


CaO

, w

t. %


0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


K2O

, w

t. %


15

16

17

18

19

20

21

22

23

24

25

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


Rb,

ppm


5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


La,

ppm


10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sam

ple

/ C

hond

rite

1956

2007

Changes in mineral assemblageChanges in mineral assemblage

Juvenile clast from the pyroclastic flow of the catastrophic eruption. Note rimm ed

hornblende and dusty-zoned plagioclase. 3/30/56

0.4 mm0.4 mm

P lagioclase > H ornblende > O rthopyroxene > C linopyroxene > M agnetite > Ilmenite z

P lagioclase > H ornblende

± Q uart

O rthopyroxene > C linopyroxene > M agnetite Ilmenite± ±

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Tim e, ca lendar years

Hornblende core in a OPx-CPx-Mt aggregate of the May 9, 2006 andesite

HbHb

0.4 mm0.4 mm

Juvenile clast from the pyroclastic flow of the . Hornblende is exceptionally rare,

however it’s remnants abaund. 5/9/06

0.4 mm

BB

AAAA

90

CC

DD

EF

EF

Plagioclase texture and compositionPlagioclase texture and composition

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140 160

R e la tive d is ta n c e , c o re to rim , m icro n s

An

,m

ol.

% A

B

30

40

50

60

70

80

90

0 100 200 300 400 500 600 700


An

,m

ol.

%

C D

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140 160


An

,m

ol.

%

EF

1956 magma1956 magma

Plagioclase texture and compositionPlagioclase texture and composition

30

40

50

60

70

80

90

0 100 200 300 400 500

Relative distance, core to rim, microns

An

,m

ol.

%

A

B

AA

BB

AA

BB30

40

50

60

70

80

90

0 100 200 300 400 500 600 700

Relative distance, core to rim, microns

An,

mol

.%

A B

Dec

embe

r 24

, 200

6D

ecem

ber

24, 2

006

May

12,

200

7M

ay 1

2, 2

007

Glass compositionGlass composition

0

1

2

3

4

5

6

64 66 68 70 72 74 76 78

SiO2, wt.%

CaO

, wt.%

May 9, 2006

Open symbols – inclusionsFilled symbols – matrix glass

Dec. 24, 2006

May 12, 2007

0

1

2

3

4

5

6

64 66 68 70 72 74 76 78

SiO2, wt.%

CaO

, wt.

%

May 9, 2006

Open symbols – inclusionsFilled symbols – matrix glass

Dec. 24, 2006

May 12, 2007

Glass compositionGlass composition

54

55

56

57

58

59

60

61

62

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010


SiO

2, w

t. %


Summary of observations and conclusionSummary of observations and conclusion

Since 1956 Bezymianny erupts magma, which becomes Since 1956 Bezymianny erupts magma, which becomes progressively more mafic with time.progressively more mafic with time.

On a smaller scale, there are periods, during which the erupted On a smaller scale, there are periods, during which the erupted products become more silicic. These short-term variations are products become more silicic. These short-term variations are superimposed on the general trend.superimposed on the general trend.

The sequence of 2006-2007 products may represent one of such The sequence of 2006-2007 products may represent one of such examples, which is corroborated by our glass data. The composition examples, which is corroborated by our glass data. The composition of melt inclusions in the outermost “dusty” zones of plagioclase of melt inclusions in the outermost “dusty” zones of plagioclase phenocrysts and the composition of matrix glass form a linear trend phenocrysts and the composition of matrix glass form a linear trend with time becoming more silicic.with time becoming more silicic.

This suggests that the outermost “dusty” zones of plagioclase This suggests that the outermost “dusty” zones of plagioclase phenocrysts form immediately prior to each individual eruption. phenocrysts form immediately prior to each individual eruption.

These observations are consistent with a view that Bezymianny These observations are consistent with a view that Bezymianny magma system is frequently replenished by mafic inputs, which magma system is frequently replenished by mafic inputs, which change overall composition of the magma system and may serve change overall composition of the magma system and may serve as eruption triggers.as eruption triggers.

2006-2007 eruptions of bezymianny volcano, kamchatka: petrological snapshots of the compositionally...

Documents