2. Classic survey of part of the Mid-Atlantic Ridge in 1970s.
Provide understanding in pattern of volcanism, fissuring, rifting and
dykes injection that occur along ocean ridge axes.
Start in 1971.
As theory of sea floor spreading and plate tectonic being
accepted.
Right time plate are generate ( oceanic ridge).
Area of study:
Small segment of Mid-Atlantic Ridge, southwest Azores.
Boundary between African and American plate.
Reason this area chosen:
Aeromagnetic survey show clear central magnetic anomaly.
Not far from port of Ponta Delgada .
A series of bathymetric survey carried out to produce maps.
On maps (Figure 4.5), transform fault can be seen.
Figure 4.6Inner rift floor is 2.5km depth and contain small hills
such as Mount Venus and Mount Pluto.
3. TECHNIQUE.
Almost every marine geological and geophysical
was used.
Many technique not for marine studies and had to
be modified for FAMOUS project.
4. NAVIGATION SYSTEM.
High precision required cause navigation problem
become acute.
Solved by:
By develop acoustic navigation system.
Used acoustic transponder placed on sea floor and
linked to ship and submersible.
Equipment proved adaptable.
Can be used with other instrument packages that
towed near sea-floor.
5. SIDE-SCAN SONAR.
GLORIA is a side-scan echo-sounding system contribute by
British.
Gave image of sea-floor topography.
The topography photo is built up by mosaic the records.
For FAMOUS, side-scan sonar mosaic obtained by
combine overlapping sonographs.
Useful for:
Identify the major fault scarp.
Determine the limit extent of fracture zone .
6. LIBEC
(LIGHT BEHIND CAMERA SYSTEM).
Overcome field of view (FOV) and
underwater photo quality that cause by
limited light scattering.
High intensity LIBEC towed above sea floor
and give large area photo.
By taking many photo in rapid succession
proved possible to build photomosaic of
sea-floor.
7. The LIBEC system shot 120-foot-
wide sections of the seafloor that
were pieced together. (Courtesy of
U.S. Naval Research Laboratory)
Project FAMOUS used the U.S.
Navy’s LIBEC camera system, which
suspended high-intensity electronic
flash lamps well above the ocean
bottom.
8. NARROW-BEAM ECHO –SOUNDER..
Conventional echo-sounder beam width about 30º.
Inadequate as the resolution more than 1km.
Using US navy system (ALVIN) with beam width 2º.
Much smaller object can be detect.
Give submersible preparation guide.
System have same FOV with submersible.
Ease the manned submersible survey.
Submersible designed with titanium hull for it work
under high pressure.
Various sampling devices added:
One arm manipulator pick specimen.
Bag to collect loose sediment.
10. INTERPRETATION OF FAMOUS
DATA…
Assumption…
The features on the topographic map is the result of
volcanism.
Thus, each hill-like feature should have volcanic
vents at or near the top and flow direction radiating
from it.
11. EVOLUTION OF THE RIFT-VALLEY
FLOOR…
Figure 4.15 and 4.16 shows the successive stages
in the formation of 2 – 3 km wide strips of new
oceanic crust either side of the Mid-Atlantic Ridge
during the last 200,000 years.
The process are consistent with a (half) spreading
rate of 1 - 2cm per year.
12. EVOLUTION OF THE RIFT-VALLEY
FLOOR…
The frequency of volcanic events varies
appreciably. By the time it was built up, each
volcano would be underlain by a swarm of dykes
emanating from the magma chamber beneath.
Subsided and rifting process occurred. Rifts mostly
form beside either to the east or the west of each
volcano. Each new phase of volcano-building
develops about the latest rift. New volcanoes will
take up space so the older volcanoes are move
aside to accommodate them.
13. EVOLUTION OF THE RIFT-VALLEY
FLOOR…
About 100,000 years old, the volcanic hills are
sufficiently far from the axis to be uplifted by faults
which mostly dip inwards from the walls.
After 200,000 years, the volcanoes heave been
upfaulted completely out of the valley floor to the
tops of the walls.