Compositional Trends at Bezymianny Volcano(1955-2008 eruptive period)

1 Geophysical Institute, University of Alaska Fairbanks

2 http://gps.alaska.edu/PIRE/index.html

Pavel Izbekov1 and PIRE team2

Historical perspective: JKASP was first

Historical perspective: Int. Volc. School

Partnership in International Research and Education (PIRE project)

PIRE-Kamchatka: Scientific goal

How an edifice collapse affects magma system of an active volcano and its following eruptive activity?

What can we learn about Mount St Helens looking at its Russian analogs – Bezymianny and Shiveluch?

Mineral assemblage vs. time

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

X

X

Whole rock and matrix glass compositions

54

56

58

60

62

64

66

68

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

Time of eruption, calendar years

SiO

2, w

t. %

, W

hole

roc

k

60

65

70

75

80

85

SiO

2, m

atrix

gla

ss

Whole rock

Martrix glass

4

4.5

5

5.5

6

6.5

7

7.5

8

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

Time of eruption, calendar years

CaO

, w

t. %

, W

hole

roc

k

0

1

2

3

4

5

6

CaO

, m

atrix

gla

ss

Whole rock

Martrix glass

Whole rock and matrix glass compositions

Whole rock and matrix glass compositions

1

1.5

2

2.5

3

3.5

4

4.5

5

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

Time of eruption, calendar years

MgO

, w

t. %

, W

hole

roc

k

0

0.5

1

1.5

2

2.5

3

MgO

, m

atrix

gla

ss

Whole rock

Martrix glass

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

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

Time of eruption, calendar years

K2O

, w

t. %

, W

hole

roc

k

0

1

2

3

4

5

6

K2O

, m

atrix

gla

ss

Whole rock

Martrix glass

Whole rock and matrix glass compositions

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

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

Time of eruption, calendar years

K2O

WR/K

2Ogl

ass

Whole rock and matrix glass compositions

What is the meaning of the observed compositional variations at Bezymianny?

Sequential withdrawal from the top of compositionally zoned magma system / column?

54

56

58

60

62

64

66

68

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

Time of eruption, calendar years

SiO

2, w

t. %

, W

hole

roc

k

60

65

70

75

80

85

SiO

2, m

atrix

gla

ss

Whole rock

Martrix glass

Magma column goes backward?

Single basaltic injection in 1955?

54

56

58

60

62

64

66

68

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

Time of eruption, calendar years

SiO

2, w

t. %

, W

hole

roc

k

60

65

70

75

80

85

SiO

2, m

atrix

gla

ss

Whole rock

Martrix glass

Requires effective but gradual admixture of mafic end-member to the 1956 magma. Convection of the crystal-rich magma would be problematic.

Repetitive / continuous basaltic injections through the 1956 magma body?

54

56

58

60

62

64

66

68

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

Time of eruption, calendar years

SiO

2, w

t. %

, W

hole

roc

k

60

65

70

75

80

85

SiO

2, m

atrix

gla

ss

Whole rock

Martrix glass

What is the frequency of recharges? Before each eruption? What controls the composition of magma at the exit? What is the composition of the mafic end-member and where are the xenocrysts?