Only one major announcement Exam Weds. March 7, review March 5, here, 5 PM

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?

I told someone I would do this (clickers, please: let’s review a bit…)

After Wednesday’s exercise and lecture on magma composition (basalt, andesite, dacite, and rhyolite), I was 1.completely confused 2.a bit confused, but mostly I got it 3.pretty much fine, it makes good sense 4.not here, so it doesn’t matter

Here’s 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 SiO 2, called polymers)

SiO 2 Basalt has <50% Andesite has ~50% - 63% Dacite has ~63% - 68% Rhyolite has >68% Do not memorize these numbers

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: that’s the part about leader/assistant/other moving around and trying to get out the door

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)

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 There’s a whole lot of apples in the magma compared to anything else…

Another clicker question (more Montserrat)

If you are down on the lower flanks of Mt Unzen, Japan, the safest place to be during a pyroclastic flow is 1.In the valley 2.On a ridge on the outside bend of the river valley 3.On a ridge on the inside bend of the river valley 1 2 3

What is the general relation between temperature and how easily magma moves? 1.The cooler the magma, the more easily it flows 2.The hotter the magma, the more easily it flows 3.Dacite is a high-temperature magma and so flows less easily 4.Dacite is a high-temperature magma and so flows more easily

Here’s 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 SiO 2 ) = VISCOSITY!! (You know it from changing the oil in your car)

Clicker Q

What kind of lava is this? Basalt Andesite Dacite Rhyolite

IN YOUR GROUP (or with 1-2 other people) 1. Don’t 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 your 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

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

Basalt volcanoes shield

SP Crater, AZ Capulin Volcano, NM cinder cone

Ukinrek volcano, AK maar