Download Volcanism 3

• Dynamic types related to magma/water
interactions
• Dynamic types related to dissolved
bubbles
• Dynamic types related to domes growth
and collapse
• Dynamic types related to lava flows etc.
• Complex edifices
• Destruction of volcanic edifices
a
vent
0
10 km
scale
sea level
Shield Volcano: Mauna Loa, HI
b
c
d
Cinder Cone:
Dome: Sunset Crater, AZ
Composite Volcano:
Lassen Peak, CA
Mt. Rainier, WA.
Figure 4-2. Volcanic landforms associated with a central vent (all at same scale).
Réunion island
Réunion Island
Piton des Neiges (3100 m)
(extinct)
Piton de la Fournaise (2600 m)
(active)
Lava flows and more lava flows…
But note also the grey material at the bottom…
Helicopter view, NW coast (btw, this cliff tends to collapse quite often on the road)
Cones groupe in Réunion + flows
Shield volcano
• Mostly a pile of basaltic flows!
• Strombolian & Hawaian
Stratovolcanoes
Figure 4-3. a. Illustrative cross section of a
stratovolcano. After Macdonald (1972),
Volcanoes. Prentice-Hall, Inc., Englewood
Cliffs, N. J., 1-150. b. Deeply glaciated
north wall of Mt. Rainier, WA, a
stratovolcano, showing layers of
pyroclastics and lava flows. © John Winter
and Prentice Hall.
Lava flows…
(Here, in the caldera wall on the top of Mt Pelée)
… and explosive phases
And erosion.
Shield volcanoes vs.
stratovolcanoes
Shield volcanoes
• Basaltic
• Intraplate (hotspot)
• Relatively flat
• Effusive (lava flows,
strombolian cones)
• Minor explosive
events (phreatic)
• Erosion and flank
collapse
Stratovolcanoes
• Andesitic to dacitic
• Subduction
• Rather steep
• Explosive
(plinian/pelean)
• Minor andesitic flows
a
• Erosion, lahars and
flank collapse
• Dynamic types related to magma/water
interactions
• Dynamic types related to dissolved
bubbles
• Dynamic types related to domes growth
and collapse
• Dynamic types related to lava flows etc.
• Complex edifices
• Destruction of volcanic edifices
Erosion and rivers
Successive valleys and valley fills
(Réunion Isl.)
Lahars
« Normal » landslides
Cilaos
Major landslides?
Major debris avalanches forming
the populated plateaux…
Successive avalanches in the core
of the volcano
Consolidated breccias
Megabreccias
(Well, Ok, not in Réunion isl…Sorry, did not find photos from there)
Superposition of breccia and flows!
.. And more
breccias
Evidence for successive events:
Breccia cut by dykes
.. How
major?
Piton de la Fournaise
Rift zone = major sliding plane?
Evolution by successive flank
collapses?
A new view on shield volcanoes:
• A succession of lava flows, and erosion
– Local erosion (lahar, valleys)
– Local/big erosions (large landslides, big
depressions)
– Major landslides (flank collapse), might be
associated with eruptions (as in MSH, but no
hard evidence for that)
Volcanic islands:
Tropical paradises or heaps of rubble?