Galapagos Rift (Pacific Ocean): Mid-Ocean Ridges
1. Zoom from Japan to the Galapagos Islands.
2. Show Map of Galapagos Islands
3. Show Photos of Galapagos Islands
a. 15 main islands, 3 smaller ones, and 107 rocks and islets
b. (see the animated tour at
http://en.wikipedia.org/wiki/Gal%C3%A1pagos_Islands)
4. Brief History of Galapagos
a. Discovered by accident in 1535 by Fray Tomas de Berlanga, Bishop of
Panama. Couldn’t find much fresh water, and many crew members
died.
i. “dross, worthless, because it has not the power of raising a
little grass, but only thistles”
ii. So, ignored by Spain, but called “Insulae de los Galopegos” for
the giant tortoises that Berlanga saw.
b. But soon became a haven for English pirates, preying on Spanish
galleons
i. Pirate Ambrose Cowley (1684) made the first map of the
islands
ii. Began capturing the tortoises for meat on long sea voyages
c. By the late 1700s, pirates were replaced by whalers.
i. English whaling captain James Colnett made the first accurate
map of the archipelago, and set up a Post Office Barrel
1. Whalers might spend years in the Pacific at a time, and
they would leave letters in the barrel that a ship would
pick up when it was returning to England. (It is still
there)
ii. Took as many as 200,000 tortoises during the 1800s, driving
them to extinction on many islands
iii. Single ships took as many as 700 at a time
iv. Fur seals were also driven to extinction
v. In 1812, a few goats, brought for food, escaped. Eventually
became over 100,000, devastating the native plants and
helping to drive tortoises to extinction.
vi. One of the visiting whalers, Herman Melville, visited and was
not impressed by the volcanic islands: "five and twenty heaps of
cinder dumped here and there in an outside city lot,” but wrote a
story in 1854, Los Encantadas (the Enchanted Isles).
d. When Charles Darwin arrived on the ship The Beagle in 1835,
however, he was impressed.
i. Darwin was young, but has spent several years with the
famous geologist Charles Lyell.
ii. Was fascinated with the geology of the Galapagos, and made
many important discoveries in the 5 weeks he was there.
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iii. Overshadowed, of course, by his many observations of beetles,
finches, etc., that led to his brilliant and revolutionary
realizations about evolution.
Briefly describe geology of Galapagos
a. Hot spot volcanoes (different kind than Fuji) – more later (with
Hawaii, Yellowstone, and Iceland)
b. Many active volcanoes, some with very unusual “inverted soup bowl”
shapes
c. Famous 1968 collapse of the Fernandina caldera
d. Fernandina erupted in 2009
e. But it is the proximity to something else that enhances the volcanic
activity of the islands: a mid-ocean rift. And it is THIS feature that is
the focus of this lecture
Right off the coast of the islands, to the north, is the Galapagos Rift.
a. It was the first ever visited mid-ocean ridge, in 1977.
Galapagos Rift is the plate boundary between two separate pieces of the
Pacific Ocean seafloor.
a. These are considered different Plates (Nazca and Cocos).
b. Show Galapagos Rift/Islands bathymetry
c. Show and explain diagram of mid-ocean ridge: Factory for making
oceans
d. Describe 70,000 km long chain of mid-ocean ridges, snaking through
and connecting all of the oceans.
Describe discovery of the Galapagos Rift
a. Describe Heat flow enigma – according to plate tectonic theory, ocean
heat flow measurements (describe) SHOULD get much higher as you
approach a ridge, but they DIDN’T.
b. Scientists suspected that the heat might be escaping rapidly out of
thermal vents right at the ridge, and decided to try to visit.
c. 1972-1974: remote evidence did find hot water at the rift, and also
some unusual mounts 75 feet high. Needed to send a human.
d. 1974: first visit with Alvin. Huge US/French mission – 5 ships and a
dive in Alvin. Disaster. Don’t find the thermal vents, but Alvin gets
stuck in a crack, and only after a long time rocking back and forth does
it escape.
e. Over the next 2 years, a deep-tow instrument finds evidence of hot
water at the Galapagos Rift, as well as long empty clamshells. Left a
transponder on the sea floor.
f. On Feb 17, 1977, the site was revisited by a manned dive within Alvin.
As Bob Ballard writes, ““coming out of small cracks cutting across the
lava terrain was warm shimmering water that quickly turned cloudy
blue as manganese and other chemicals in solution began to
precipitate out of the warm water and were deposited on the lava
surface, where they formed a brown stain.” (Robert Ballard, Oceanus
Magazine, 1977).
g. Each new dive began to find new discoveries, like foot-long clamshells
and many life forms never seen before. Richard Lutz wrote “Literally
every organism that came up was something that was unknown to
science up until that time. It made it terribly exciting. Anything that
came [up] on that basket was a new discovery.”
h. John Edmond wrote “We all started jumping up and down. We were
dancing off the walls. It was chaos. It was so completely new and
unexpected that everyone was fighting to dive [in Alvin]. There was so
much to learn. It was a discovery cruise. It was like Columbus.”
9. Thermal vents and incredibly diverse and bizarre biological communities
have now been found at many mid-ocean ridges.
a. Show pictures, footage, animations, of thermal vents and biologic
communities.
i. Towers, pillow basalts, etc.
b. We now understand how they work, and what the answer to the heat
flow problem was.
c. Draw a diagram and explain mid-ocean ridge water circulation.
i. Explains missing heat on the flanks; >400C temps at the ridge.
ii. Dissolution/Precipitation – explains the black water, tall
towers (50 feet!), and layer of minerals.
iii. Explains life – needs water, heat, and food. Extremophiles live
off of all kinds of minerals in the water, and form the base of a
complex food chain with NO LIGHT.
10. As well as being a true Geological Wonder, mid-ocean ridges like the
Galapagos Rift have a personal human significance that extends beyond this.
a. They may be where life originated on the planet, more than 3.5 billion
years ago.
i. They may be the kind of place to go look for life on other
planets (NASA Astrobiology program).
b. We may need these minerals.
i. Talk about incredible human need for resources, and the
dwindling supplies
ii. Give numbers for years remaining for certain minerals
iii. Many of the minerals we mine actually were separated from
the crust at mid-ocean ridges (brought into subduction zones
and concentrating)
iv. May one day just take big hoses down there and suck the stuff
up.
11. For the Top 5, I am in a bit of a quandary
a. I chose the Galapagos Rift because it was the first discovery, and there
is an amazing place right nearby (the Galapagos Islands), where you
CAN visit. And, some people (including teachers) DO get to dive down
to the Galapagos Rift.
b. There is one other location, Iceland, where the mid-ocean ridge comes
up on land (but Iceland will have its own lecture, in #XXX).
c. So, what do I do for the other locations? The rest of the mid-ocean
ridge chain is underwater.
d. Well, if we can’t go to the rifts, there are places where the rifts have
come to us!
e. Define Ophiolite
f. 4 most famous places where you can visit rock that was once at an
undersea mid-ocean ridge and shows all of the different layers:
i. Semail (Oman, UAE)
ii. Troodos (Cyprus)
iii. Bay of Islands (Newfoundland)
iv. Papua Ophiolite (Papua, New Guinea)
12. Next, will shift directions and head to the Canadian Rockies to look at the
Burgess Shale.
Questions:
1. Life that exists at mid-ocean ridges rarely survives
when it is brought up to the surface. Why do you think
this might be?
2. The basaltic rock covering the surface at mid-ocean
ridges is often in the form of pillowy shapes. Why don’t
you see these on the seafloor in older rocks, away from
the ridge?