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Vol Lecture Notes 8

The great mobility of the krakatau flows from the 10

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Unformatted text preview: esult of enhanced runout over the sea. It is proposed that the generation of steam at the flow/seawater interface may have led to a reduction in the sedimentation of particles and consequently a delay in the time before the flows ceased lateral motion and became buoyantly convective. The buoyant distal edge of these ash-and steam-laden clouds lifted off into the atmosphere, leading to cooling, condensation, and mud rain.” 10 Pyroclastic surges are Pyroclastic Surges dilute, high energy pyroclastic density currents that typically produce thin, bedded and cross-bedded to massive deposits. Pyroclastic surges are commonly associated with phreatomagmatic explosions, but may also be associated with other phenomena, such as dry volcanic explosions and pyroclastic flows. In reality, surges and flows form a continuum - with grain density and turbulent energy main factors. Characteristics of Pyroclastic Surge Deposits Partially topographically constrained T h in o v e r h ills , th ic k e n in v a lle y s Sorting variable W e a k to g o o d V e r y c o a r s e c la s ts a n d b lo c k s o f p y r o c la s tic flo w s g e n e r a lly la c k in g F in e s t fr a c tio n a ls o la c k in g N o t a s w e ll s o r te d a s fa ll d e p o s its Often show evidence of lateral transport R ip p le s B a s a l s c o u r in g C r o s s b e d d in g Highly fragmented (generally small grain size) 11 Generation of Surges B a s e S u rg e Explosive interaction of magma and water Eruptive colu...
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