“It looks kind of like a lava lamp.” — ALAN LEVANDER
Grand Canyon’s high surroundings
may be product of continental lift
By Alexandra Witze
For all its glorious views, the Colorado
Plateau remains an ugly mystery to geologists. They can’t figure out why and how
it rose thousands of feet over the millions of years it took to carve spectacular
natural wonders like the Grand Canyon
and Monument Valley.
The answer may lie deep beneath the
plateau’s chiseled landscape, a study in
the April 28 Nature suggests. Hot rock
welling up from below invades the plateau, causing blobs to drip off the bottom.
“It looks kind of like a lava lamp,” says
the study’s leader, Alan Levander of Rice
University in Houston.
Geologists have wondered about the
high plateau’s origin ever since early
explorers stood on the edge of the
Grand Canyon and peered down at the
Colorado River through 1,500 meters of
layer-cake rock.
The geologic province roughly covers
the Four Corners area where Utah, Colorado, New Mexico and Arizona come
together. About 2 kilometers above sea
level, the plateau behaves as a single,
mostly undisturbed chunk of crust even
as tectonic forces crumple the landscapes on either side.
To the east, the Rocky Mountains
thrust toward the sky; to the west, the
Basin and Range province wrinkles in
long ridges of mountains and valleys.
But something, mysteriously, has kept
the Colorado Plateau high and intact.
Most theories focus on the uppermost layers of the Earth’s innards: the
4
Lava lamp Partially molten material from
Earth’s interior (gold) may trigger slabs of crust
to peel off and “drip” back down (blue), perhaps
explaining the rise of the Colorado Plateau (top).
Elevation (km)
2
0
0
50
Depth (km)
The Colorado Plateau may have risen
through a geological process that peels
away material from below.
freezes, weakening the lithosphere and
eventually chiseling chunks of rock away.
Over time, more blobs fall off, lightening
the plateau and allowing it to rise upward
like a floating cork.
Geologists have previously spotted
other places where blobs might once have
dripped, Levander says, such as along the
Some scientists, though, aren’t yet
convinced. “The tendency is to say we
have what looks like a drip and therefore
it is a drip,” says geophysicist Mousumi
Roy of the University of New Mexico in
Albuquerque. “We need to be really careful about that interpretation.” Two years
ago, Roy and her colleagues described
an alternate theory to explain plateau
uplift, in which the lithosphere warmed
but did not drip.
In particular, she says, the new work
assumes that rock infiltrating from
below would make the lithosphere more
dense by rearranging atoms such as iron
into minerals with less space between
the atoms. But this “refertilization” process is messier in real life than in theory,
Roy argues. The chemical changes aren’t
well understood, she says, and probably
don’t lead to chunks of lithosphere getting more dense and breaking off.
The drip theory can’t explain all of the
plateau’s uplift, Levander notes. He and
his colleagues are now looking for drips
