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Unformatted text preview: surges across volcano's broad icecovered summit. formed when ﬂow meets heavy rain, ice melt, rivers
extremely dangerous Río Lagunillas, former location of Armero. Within 4 hours of
beginning of eruption, lahars had traveled 100 km: more than
23,000 people killed, about 5,000 injured, and more than 5,000
homes destroyed .
Images: USGS volcanoes hazards site:
35 Pyroclastic deposits – types of lithified rocks i. volcanic tuff - rock composed of pyroclastic
fragments and ash
a. welded tuff - fragments melt together on deposition Image source: Hamblin and Christiansen (2001) b. ash ﬂow tuff - tuffs from ash ﬂowing across surface
c. air fall tuff - tuff from ash settling from atmosphere Piton del Teide (Canary Islands) - thick pumice layers (white in this image) interbedded with more locally-derived dark
basaltic ash. image -Volcano World site: http://volcano.und.nodak.edu/vwdocs/volc_images/africa/piton_teide2.html]
36 12 8/27/2012 Pyroclastic deposits – types of lithified rocks ii. Volcanic Breccia Volcanic breccia (view is 0.3 m)
[image source: Press and Siever, 2001]
Volcanic breccia. Notice angular rock fragments consisting
of flow-banded rhyolite.
37 Intrusive (plutonic) processes and bodies difﬁcult to observe crystallizing intrusive body but
infer shape and size
1. Tabular intrusive bodies Sill - tab intrusive that are concordant (along bedding
image source: Winter (2010) 38 Intrusive (plutonic) processes and bodies Dike - tab intrusive discordant Sills Salsbury Crags, Teschenite Sill (Edinburgh) Dolerite sill from Ross Sea, Antarctica
Image source: www.rosssea.info/geology.html Sill from Big Bend, Texas 39 13 8/27/2012 Intrusive (plutonic) processes and bodies dike - tabular intrusive that is discordant i.e. cut
across bedding/layering of country rock Dike cutting shales in the lower Grand Canyon Radial dike around volcanic neck at Spanish Peaks, CO Types of dikes cutting stratal
features: (a) simple dilation and
injection of magma (b) no
dilation, but replacing or stoping.
image source: Winter (2010) 40 Intrusive (plutonic) processes and bodies Veins - de...
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This document was uploaded on 07/18/2013.
- Fall '09