Some questions are just fun to get. Perhaps it’s the
teacher in me that likes to see young eyes light up with intellectual
excitement. I infer from the following that volcanoes first get talked about seriously in the 5th
Grade. It's beyond the soda, vinegar, and food coloring lesson.
Q:
Question for my 5th grade class!
My
students have some questions,
- Megan A
1.
Why do volcanoes erupt?
A: Pressure builds up from rising low-density magma
below the earth. The low density is caused by the heat from the Mantle and Core
of the Earth convecting upwards, sorta like a pot of Cream of Wheat cooking, or
a lava lamp. The path of least resistance is to break out through the Earth's Crust
at its weakest point. Where are those weakest points? Well, where you now see
volcanoes is a pretty good hint. Some geologists have speculated that when tectonic
events leave faults, and two faults happen to cross, that may make the
intersection a “target of opportunity” for rising magma. However, there are a
number of other factors involved, including where is the magma rising, and from
what source, is there some under-plating of the crust happening, are there some gross
compositional differences in the crust, etc.
2.
What are volcanoes like?
Some volcanoes look like cones (Mount Hood in Oregon, Mount Fuji in Japan). Some
look like giant bulges (Mauna Loa in Hawai'i). Some volcanoes don't look like much of anything.
You just see black-gray lava that has broken out of fissures, then poured out
and run across the land in all directions – but generally the "pouring" goes downhill. There are vast, nearly impassable volcanic fields in western Saudi Arabia. There are
huge obsidian flows (volcanic glass, caused by lava emerging in water and cooling too rapidly to form mineral grains) at Medicine Lake volcano in California. These look like a
giant painted the ground with swirling green-black glass.
3.
What is lava like?
Lava is very hot initially when it first reaches the
air - it glows yellow-red from incandescence in cracks and at the flow-fronts.
You can walk on it, because it is denser than a human body, but it is pretty
rough on your boots. It melts boot-soles while hot, and cuts them up when cold
because lava (e.g., in Hawai'i) is really just black glass. As lava cools, it sounds
like a bowl of Rice Crispies crackling. As the flow-front reaches trees and houses,
it engulfs them and the very high heat sets them on fire. This often forms tree molds - molds of where trees once were before being engulfed by the lava, for instance in HAwai'i and at Newberry Volcano in central Oregon. On Mauna Loa, a fast moving flow-front in the 1950's burst out of a fissure high on the volcano's west flank. I talked with a man who watched the flow run down the volcano's flank and onto a forest. It clipped off the
trees at the base, then stack them vertically like bunched toothpicks at the front of the flow as the whole thing raced downhill at 60 kilometers per hour into the Pacific Ocean.
4.
Have you seen a volcano erupt?
I was inside Mutnovskiy volcano in Kamchatka when it
started venting. I watched Mount St Helens erupt several times in 2004-2005.
I've walked over active (evolving, moving) lava fields from Kilauea volcano,
tracking the growing flow-front using a GPS device.
5.
Is your job dangerous?
Not any more dangerous than driving a car on a
Friday night when there are drunks on the road. Most volcanologists know
someone, a friend or a colleague, who has died while working on a volcano, so yes, volcanoes ARE
dangerous, and must be treated with respect. Because volcanoes are so dangerous, we take extra precautions when
working on one that is restive, and generally stay well away of they are erupting. It's sort of like wearing seatbelts
when you drive in a car. If you don't you are being deliberately careless - and statistically you have a much higher chance of dying.
