Transcript (with Death Valley) Geoscience 10: Geology of The National Parks

The EARTH: Its HOT Inside!
Geoscience 10: Geology of The National Parks
Unit 2
The EARTH: Its HOT Inside!



The deeper a mine or oil well is, the hotter it
is at the bottom; volcanoes bring up heat
from below;
Earth’s heat made mostly by decay of natural
radioactive atoms in rocks;
How materials (and people!) behave depends
on what they are (iron, silica, etc.) and on the
conditions they are placed in (heat,
pressure);
Geoscience 10: Geology of The National Parks
Unit 2
EARTH: Layered by Composition & Behavior




Iron core, mantle with silica added to iron, ocean crust with
more silica, continental crust with still more silica (way more
complex than this, but this is a start)--going up, each layer
less dense and floats on layers below;
Core has solid inner part (higher pressure squeezes to solid)
and liquid outer part;
Crust plus upper mantle (called lithosphere) tend to break not
flow; deeper in mantle tends to flow not break
(asthenosphere, plus other names and layers we won’t worry
about) (hot solids can flow--think of chocolate bar in your
pocket, or blacksmith making horseshoes);
Mantle and crust solid, but with a little melt in few places.
Geoscience 10: Geology of The National Parks
Unit 2
CONVECTION: Moving the Mantle’s Heat




Heating causes expansion & rising, cooling causes
contraction & sinking; together form convection cells (in
spaghetti pots on stove, and in soft part of Earth’s
mantle)
Lithosphere broken into a few big plates that raft around
on the convection cells like scum on a spaghetti pot;
Where the lithospheric plates are pulled apart, they tend
to break. The breaks often slant down, and one side
slides down along the other, making an earthquake fault;
Death Valley is a great example!
Geoscience 10: Geology of The National Parks
Unit 2
Nevada Getting Wider (with Death Valley)




Lake Tahoe (California) and Snowbird (Utah) ski
areas are moving apart about as rapidly as your
fingernails grow (an inch or so per year)--can
measure with GPS, etc.
We find layers of rock offset as shown in the
diagram, and earthquakes still happen and increase
that offset;
Lava may leak up the cracks to feed volcanoes;
If this kept on, could tear the west apart to make an
ocean basin;
Geoscience 10: Geology of The National Parks
Unit 2
DEATH-VALLEY: Tear-Apart Makes Oceans

That’s what Gulf of California is;

Baja California is drifting away from mainland;




The breaking of the rocks has focused along a crack
down the middle of the Gulf;
As the rocks move away from the crack, their weight
no longer squeezes the hot mantle beneath the crack;
For most rocks, squeezing tends to make solid, and
“unsqueezing” (a drop in pressure) favors melting;
So the hot mantle under the crack melts a little, and
the melt leaks up the crack and freezes.
Geoscience 10: Geology of The National Parks
Unit 2
DEATH-VALLEY: Tear-Apart Makes Oceans






The sea floor of the Gulf of California (and of all other
oceans!) is made of the frozen crack-filling lava;
The sea floor is hottest, and thus highest, near the crack,
forming a mid-oceanic ridge;
Such ridges wind through Earth’s oceans like the seam on a
baseball;
Ocean-floor rocks are youngest near the ridges, oldest
farthest from the ridges;
Sediment (wind-blown dust, fish poop, etc.) thickens away
from the ridges because older rocks have had more time for
fish to poop on them;
Where ridges come up on land, they are ripping continents
apart, as at Death Valley and in the East African rifts.
Geoscience 10: Geology of The National Parks
Unit 2