Lab 10: earth: volcanoes: magma, gases and spectra
Detecting the gas composition of a volcano is important in predicting impending eruption.
There are two types of magma, based on chemical composition:
- Basalt is runny, less-viscous magma that flows freely and creates the volcanoes we have in Hawaii
- Andesitic is sticky, more viscous and forms the cone shaped volcanoes in the Andes (hence the name), Japan, Indonesia, Mexico, and Italy.
Magma is under the surface, Lava is once it reaches the surface, both are classed as igneous rock.
Once magma reaches the surface, it becomes lava, and can then solidify into several forms:
a'a is the Hawaiian name for rock that cools very quickly, while gases are still bubbling from the lava
pahoehoe is the ropey rock that is formed when lave cools more slowly
obsidian is the glass like rock formed if the lave cools very slowly
Pumice is a version of a'a
Pele's hair is magma that solidifies in the air, making strands of rock
Vog is small particles of pumice with sulfuric acid in the small spaces-very irritating
Part 1: Magma temperature
- Using the massive lenses we have in the lab below, and using the Darth Vader helmets or goggles for protection, focus the sunlight on any rock you find on this island (why not coral or concrete?)
- Using the infrared temp sensor, measure the temperature of the magma
Part 2: Volcanic gases
- Go to the purple air website and look up the air quality around our island (over 50 is bad)
- Investigate the different settings for types of volcanic gases
- Go to weather.hawaii.edu and search for the vog cloud map
- When would our air quality be poor and why?
- Challenge: pick a place on the planet that has the worst air you can find: put the numbers on the board for the class to find them
Part 3: Spectra of gases
Using a spectroscope, look at several chemical vapors such as sodium, potassium and other flame test colors
These indicate what element is present, and can be used to measure relative amounts
Questions:
- how is gas composition related to the depth of the magma?
- what sort of rock would be formed from magma cooling underwater?
- why would andesitic volcanoes explode while basaltic ones do not?
- which type is vesuvius and what happened there?
- why do volcanologists concentrate so much on expelled gases? is it a practical or scientific reason?
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