unusual volcanoes have magnetic fields that seem to defy the
Paul Doherty, with additional info from Robin Marks
earth is a magnet with north and south poles. An
electromagnet, to be specific. The Earth's magnetic field is created
by electric currents which flow in the rotating and convecting liquid
metal of the planet's outer core.
We tend to think of the
magnetic North and South poles as stationary (Santa's house doesn't
move, in other words), but they're not. They drift over time, and
neither of them are located exactly at the geographic poles. One
magnetic pole is in Northern Canada, about 15 degrees of latitude
from the geographic North Pole. The other is of the coast of Antarctica.
mountain (shrouded in clouds) is called a moberg, because it
erupted under ice. Lava on the top half matches the magnetism
of Earth today. Lava from the lower half records reversed poles.
Over time, the poles
drift enough to actually switch places, reversing each other. What
does that mean? Think of it this way: if you use a compass today,
the needle points toward magnetic north. If you used that same compass
700,000 years ago, it would point toward magnetic south. This reversal
of the poles gives scientists clues about how the earth has been
forming and changing over time.
Especially in Iceland.
Under ice in the nearby ocean, ridges and mountains have been created
by volcanic activity over millions of years. When an eruption brings
lava to the surface, the molten rock cools with a magnetism that
matches that of the Earth at the time of the eruption. So if you're
standing on a rocky mountainside made in an eruption 700,000 years
ago, your compass will point to south. If you move up higher, to
newer rock deposits, your compass will point north again.
can show yourself how a planet's magentic poles work. Try this!
You can make a 3-D model
of magnetic fields by inserting a small, strong magnet into a sphere.
If you sprinkle used staples onto the sphere, you'll see the how
the field works, as the orientation of the staples will change with
do I need?
You can buy a preassembled
earth globe with a magnet already inside from Arbor Scientific,
P.O. Box 2750, Ann Arbor, Michigan 48106 (1-800-367-6695) for about
$15 (in 2000). Or you can make you own:
- use a Sqeeshball,
a soft toy ball with an earth globe printed on it, available in
toy and trinket stores
- a Neodymium magnet
- you can make a 1 cm x 1 cm cylinder from two standard-sized
1 cm x 1/2 cm discs (only neodymium magnets are strong enough
for this. They're available from Dowling Miner, P.O. Box 1829,
Sonoma, CA 95476, 1-800-MAGNET1 or All Magnetics, 930 S. Placentia
Ave. Placentia, CA, 92670, 1-800-AMAGNET.)
- hot melt glue or silicone
- utility knife or scissors
If you're assembling
your own magnetic earth, cut a slit in the Squeeshball, and insert
the magnet into the center. Point one of the flat ends of the magnet
toward the north pole of the earth. Reseal the ball with silicone
seal or hot melt glue.
Explore the magnetic
field of the ball. If you place a used staple on the ball, the staple
will stick to the ball and line up with the ball's magnetic field.
Add more staples to the ball. Notice that the staples lie flat against
the ball along a circle, this is the "magnetic equator. " At the
"magnetic poles," the staples stand up vertically. Between the poles
and the equator the staples stand up at different angles with respect
to a plane tangent to the ball. The angle between the staple and
the tangent plane is known as the "magnetic inclination" or the
"dip of the magnetic field."
Use a compass to explore
the magnetic field surrounding the sphere. The field stretches away
from the sphere; in the same way, the earthÕs magnetic field stretches
far out into space. The earthÕs field traps charged particles from
the sun making the Van Allen radiation belts.
If the compass is held
far from the magnetic sphere it will align itself with the magnetic
field of the real earth rather than your earth model. Notice that
in North America the north pole of the magnaprobe (red) points north
The earth is a magnet
with magnetic north and south poles. Because it has only two poles,
two places where the staples stand up vertically, its magnetic field
is modeled by what is called a "dipole field."
A sphere with a magnet
inside creates a magnetic dipole like that of the earth. The staples
will line up with this magnetic field. As the staples align, they
show field lines that run between the north and south poles, they
also show that the field over most of the sphere is not tangent
to its surface. Although the magnetic field of this experiment is
created by a permanent magnet, the earth is actually an electromagnet.
The earth's magnetic field is created by electric currents which
flow in the rotating and convecting liquid metal of the earthÕs
A compass lines up with
the earthÕs magnetic field, however, the pivot of the compass does
not allow it to rotate up or down so it only shows the horizontal
component of the field.