T h is te r m is e x tr e m e ly b r o a d a n d is a

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Unformatted text preview: e r m is e x tr e m e ly b r o a d a n d is a p p lie d to a w id e r a n g e o f p h e n o m e n a th a t h a v e a v a r ie ty o f c a u s e s , b u t a ll a r e u ltim a te ly d u e to v o lc a n ic e r u p tio n s . R e la te d ( g e n e r a lly m o r e s p e c ific ) te r m s : Ignimbrite Pumice flow Block and ash flow Nuee Ardente (glowing cloud) O n e c a u s e o f p y r o c la s tic flo w s is e r u p tiv e c o lu m n c o lla p s e 4 Generation of a Pyroclastic Flow, Mt. St. Helens July 22, 1980 +15 seconds Generation of a Pyroclastic Flow, Mt. St. Helens July 22, 1980 +30 seconds 5 Generation of a Pyroclastic Flow, Mt. St. Helens July 22, 1980 +40 seconds Generation of a Pyroclastic Flow, Mt. St. Helens July 22, 1980 +60 seconds 6 Generation of a Pyroclastic Flow, Mt. St. Helens July 22, 1980 +5 minutes Deposit of the August 7. 1980 Pyroclastic Flow 7 Deposit of the October 22. 1980 Pyroclastic Flow Pinatubo Ignimbrite 8 Eruptive Column Stability W h a t c o n d itio n s le a d to c o n v e c tio n , a n d w h a t c o n d itio n s to c o lla p s e ? C o n d itio n n e c e s s a r y fo r c o n v e c tio n : ρcolumn < ρatmosphere S in c e a s h is m o r e d e n s e th a n th e a tm o s p h e r e , th e a b o v e r e q u ir e s th a t th e g a s in th e c o lu m n b e le s s d e n s e th a n s u r r o u n d in g a tm o s p h e r e R e q u ir e s : Low gas density Heat Low ash density Gas Densities & Stability A s h D e n s ity ~2.3 g/cc 2300 g/l G a s D e n s itie s 1 mole occupies 22.4 l at STP Mean molecular weight of air: ~2...
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