Transcript Dynamic Earth

http://pubs.usgs.gov/publications/text/dynamic.html
Computer-generated
detailed topographic
map of a segment of
the Mid-Oceanic
Ridge. "Warm" colors
(yellow to red) indicate
the ridge rising above
the seafloor, and the
"cool" colors (green to
blue) represent lower
elevations. This image
(at latitude 9° north) is
of a small part of the
East Pacific Rise.
The center part of the
figure -- representing
the deep ocean floor
with the sea magically
removed -- shows the
magnetic striping (see
text) mapped by
oceanographic
surveys offshore of the
Pacific Northwest. Thin
black lines show
transform faults
(discussed later) that
offset the striping.
View of the first hightemperature vent (380
°C) ever seen by
scientists during a dive
of the deep-sea
submersible Alvin on
the East Pacific Rise
(latitude 21° north) in
1979. Such geothermal
vents--called smokers
because they resemble
chimneys--spew dark,
mineral-rich, fluids
heated by contact with
the newly formed, stillhot oceanic crust. This
photograph shows a
black smoker, but
smokers can also be
white, grey, or clear
depending on the
material being ejected.
The deep-sea hot-spring environment
supports abundant and bizarre sea life,
including tube worms, crabs, giant
clams. This hot-spring "neighborhood" is
at 13° N along the East Pacific Rise.
Plate boundaries can be either active, i.e.,
divergent versus or convergent, or passive
(transform)
The Mid-Atlantic
Ridge, which splits
nearly the entire
Atlantic Ocean
north to south, is
probably the bestknown and moststudied example of
a divergent-plate
boundary.
Map showing the
Mid-Atlantic
Ridge splitting
Iceland and
separating the
North American
and Eurasian
Plates. The map
also shows
Reykjavik, the
capital of
Iceland, the
Thingvellir area,
and the locations
of some of
Iceland's active
volcanoes (red
triangles),
including Krafla.
Lava fountains (5p;10 m high)
spouting from
eruptive fissures
during the October
1980 eruption of
Krafla Volcano.
Aerial view of the area
around Thingvellir,
Iceland, showing a fissure
zone (in shadow) that is
the on-land exposure of
the Mid-Atlantic Ridge.
Right of the fissure, the
North American Plate is
pulling westward away
from the Eurasian Plate
(left of the fissure). Large
building (near top) marks
the site of Lögberg,
Iceland's first parliament,
founded in the year A.D.
930.
Map of East Africa
showing some of the
historically active
volcanoes(red triangles)
and the Afar Triangle
(shaded, center) -- a socalled triple junction (or
triple point), where
three plates are pulling
away from one another:
the Arabian Plate, and
the two parts of the
African Plate (the
Nubian and the
Somalian) splitting
along the East African
Rift Zone.