trying to escape plinys account morning of august 25

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Unformatted text preview: ealed room); continual tremors Pliny the Younger and his mother flee northward, but are overcome by clouds of ash. Hours later, the ash clears. Paroxysmal phase lasts 20 hours Pliny observes that smooth cone of Vesuvius replaced by stump and the entire region is covered in gray. 14 The Geologic Record Geologic Record: Lower Units E U 1 : b a s a l u n it Surge deposit produced by phreatomagmatic explosion (due to presence of crater lake?) E U 2 W h ite P u m ic e Thick sequence of well-bedded pumice corresponding to Plinian phase of the eruption. Found mainly to the East (indicating westerly wind) 1.5 m thick at Pompeii Accumulated at 10-15 cm/hour Discharge rates of 8 x 107 kg/s - decreases near end Column height: 26 km 15 Geologic Record: Lower Units EU 3 Grey Pumice Begins with increase in eruption rate to 1.5 x 108 kg/s Color change corresponds to compositional change Column height of 32 km, decreases to 17 km over next 9 hours EU 2 and EU 3 interrupted by at least 5 pyroclastic flows produced by column collapse The Geologic Record: Upper Units Provide evidence of phreatomagmatic events P y r o c la s tic flo w a n d s u r g e d e p o s its in te r b e d d e d w ith th in fa ll d e p o s its R ic h in lith ic fr a g m e n ts , in c lu d in g d e e p - s e a te d lim e s to n e , m a r b le s , s k a r n s Probably result from interaction of magma with regional aquifer 16 Eruption of Zoned Magma Chamber C o r r e la tio n b e tw e e n m a s s d is c h a r g e r a te a n d c o m p o s itio n : Higher discharge rates scoured deeper into magma body. Pyroclastic Flows 17 18 The Epilogue P o m p e ii a n d H e r c u la n e u m d e s tr o y e d b y p y r o c la s tic flo w s ; d e a th to ld u n k n o w n ( a b o u t 2 0 ,0 0 0 r e s id e n ts a t th e tim e ) . 4 m in Pompeii 23 m in Herculaneum A s h c o v e r le a d R o m a n s to a b a n d o n th e a r e a P o m p e ii a n d H e r c u la n e u m e v e n tu a lly fo r g o tte n R e d is c o v e r e d in 1 5 9 5 Some plundering of art over the next several centuries E x c a v a tio n b e g in s in 1 7 4 8 V e s u v iu s h a s s u b s e q u e n tly e r u p te d m o r e th a n 5 0 tim e s . 19...
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This document was uploaded on 03/04/2014 for the course EAS 458 at Cornell University (Engineering School).

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