Only one major announcement

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Only one major announcement

• Exam Weds. March 7, review March 5, here, 5 PM

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Today, more on volcanism (also see outline on
the website)

• What are the different materials that come out of
  a volcano? What are the compositions involved?
  
• What are different kinds of volcanoes?
• What makes a volcano erupt the way it does?

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I told someone I would do this
(clickers, please lets review a bit)
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After Wednesdays exercise and lecture on magma
composition (basalt, andesite, dacite, and
rhyolite), I was

• completely confused
• a bit confused, but mostly I got it
• pretty much fine, it makes good sense
• not here, so it doesnt matter

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Heres the story

• Many things make magma erupt the way it does
• temperature
• how many crystals it has
• how much gas it has dissolved in it
• And, most important to what we were doing
  Wednesday HOW MUCH SILICA (the composition,
  shows up as SiO2, called polymers)
  

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SiO2

• Basalt has
• Andesite has 50 - 63
• Dacite has 63 - 68
• Rhyolite has 68
• Do not memorize these numbers

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Fruit salad

• 20 blueberries
• 20 strawberries
• 20 kiwis
• 20 bananas
• 20 apples

As the amount of silica increases in the magma,
compared to other elements, the magma gets
stickier and stiffer and harder to move/erupt
thats the part about leader/assistant/other
moving around and trying to get out the door
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Basalt

• highest-temperature magma all magma starts life
  as basalt
  
• high-temperature minerals are really easy to
  form, but hard to preserve
  
• if you take all the blueberries out of the fruit
  salad, what you have left over will have 0
  blueberries and 25 strawberries, 25 kiwis, 25
  bananas, and 25 apples the magma becomes
  andesite

The amount of silica (apples) has increased
(compared to blueberries, for example)
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Rhyolite the 50 bananas and 50 apples left in
the fruit salad

• you started with 20 of 5 different kinds of
  fruit
  
• coolest-temperature magma
• coolest-temperature minerals form from the
  cooler-temperature ones as the magma cools
  
• chains of silica

Theres a whole lot of apples in the magma
compared to anything else
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Another clicker question
(more Montserrat)
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If you are down on the lower flanks of Mt Unzen,
Japan, the safest place to be during a
pyroclastic flow is

• In the valley
• On a ridge on the
• outside bend of the
• river valley
• On a ridge on the
• inside bend of the
• river valley

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2
3
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What is the general relation between temperature
and how easily magma moves?

• The cooler the magma, the more easily it flows
• The hotter the magma, the more easily it flows
• Dacite is a high-temperature magma and so flows
  less easily
  
• Dacite is a high-temperature magma and so flows
  more easily

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Heres the story

• Many things make magma erupt the way it does
• temperature
• how many crystals it has
• how much gas it has dissolved in it
• And, most important to what we were doing
  Wednesday HOW MUCH SILICA (the composition,
  shows up as SiO2)
  
• VISCOSITY!! (You know it from changing the oil
  in your car)
  

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Clicker Q
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What kind of lava is this?

• Basalt
• Andesite
• Dacite
• Rhyolite

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IN YOUR GROUP (or with 1-2 other people)
1. Dont talk to your group at first, answer
this question when you see this slide on the
mid-term, how will you do the describe this to
your granny part? 2. Share your answer with y
our group, and together come up with the best
possible answer 3. Talk with your group about
which of basalt, andesite, dacite, rhyolite you
clicked on and why
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For these next pictures of volcanoes

• sketch the picture, especially the shape of the
  volcano
  
• write notes on the picture that will help you
  remember key features
  
• be sure you can identify what kinds of things are
  erupted from different kinds of volcanoes

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Basalt volcanoes
shield
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SP Crater, AZ
cinder cone
Capulin Volcano, NM
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Ukinrek volcano, AK
maar