Making Rocks
Jim Webster
Here's what I do!
Step 1
Step 2
Step 3
Visit Jim's Lab
Step 3: Make a Magma Chamber
What was it like deep in the magma chamber when the pumice formed? What was the temperature? What was the pressure?

We experiment with different conditions until we have re-created the same rock. Then, we will know more about what it was like deep inside the magma chamber, before the volcano erupted.

FIRST, we prepare a mini-magma chamber
We combine all of the ingredients needed to make our own rock.

• We crush some of the pumice we collected into a fine powder.

• This goes into a tiny gold capsule, with some gas we added.

• Then, we seal it tight so the gas does not escape.

Mini-magma chamber

SECOND, we turn it into magma...and make a rock!
We put our capsule, or mini-magma chamber, under some pretty extreme conditions.

• We heat the sample to about 800 degrees C (1500 degrees F.) That's about three times hotter than your oven gets.

• We set the pressure to about 2000 bars. This is equal to the pressure exerted by the Earth about 4 1/2 miles deep.

• After the machine runs for several days, we shut it off so the magma cools quickly and hardens into glass.

Magma machine
THIRD, we analyze our new rock.
If it has the same amount of gas as the original rock, we know we chose the right temperature and pressure. If not, we try again.

It can take many experiments to discover the same conditions as the original magma chamber. But, every time that we do it, we are learning more about what makes volcanoes explode.