I. Geological Formation of Oceanic Islands. A. What is an oceanic island?
-
Upload
sofia-mcpherson -
Category
Documents
-
view
225 -
download
2
Transcript of I. Geological Formation of Oceanic Islands. A. What is an oceanic island?
![Page 1: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/1.jpg)
I. Geological Formation of Oceanic Islands
![Page 2: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/2.jpg)
I. Geological Formation of Oceanic Islands
A. What is an oceanic island?
![Page 3: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/3.jpg)
Oceanic Island:
• No direct, terrestrial connection to continent (now or in the past);
• Usually separated from continent by deep ocean.
• Usually formed by volcanic activity;
![Page 4: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/4.jpg)
I. Geological Formation of Oceanic Islands
A. What is an oceanic island?
B. Lithosphere and Plate Tectonics
![Page 5: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/5.jpg)
Cutaway Diagram of the Earth
![Page 6: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/6.jpg)
Cutaway Diagram of the Earth
Inner Core • Radius ~1255 km• Solid Iron• ~ 4100˚C• Rotates W to E
![Page 7: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/7.jpg)
Cutaway Diagram of the Earth
Outer Core • ~ 2,220 km thick• Liquid Iron-Nickel• ~ 4100˚C• Rotates E to W•Rotation generates earth’s magnetic field
![Page 8: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/8.jpg)
Cutaway Diagram of the Earth
Mantle • ~2,800 km thick• Mostly solid (“silly putty”)• Mg/Fe/SiOx (Olivine)• ~1000-3,500˚C•Heat generated by high pressure and radioactive decay (U, Th, K)
![Page 9: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/9.jpg)
Cutaway Diagram of the Earth
Upper Mantle Outer Mantle • ~ 30 to 70 km deep• Solid rock
Asthenosphere• ~70 to 300 km deep• soft - flows slowly
![Page 10: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/10.jpg)
Cutaway Diagram of the Earth
Crust• ~ 5-50 km thick• Solid, brittle rock
![Page 11: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/11.jpg)
Two Types of Crust:
• Continental crust
• Oceanic crust
Continental crust Oceanic crust
Ocean
![Page 12: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/12.jpg)
Continental Crust:
• Forms the continents
• 20 - 70 km thick (average ~ 30 km)
• Granite (Al / SiOx) = metamorphic rock
• Relatively low density (~2.7 g/cc) = buoyant
• Surface averages ~ 125 m above sea level
• Old (up to 3.8 billion years old)
• Covers ~ 35% of earth’s surface
Continental crust Oceanic crust
Ocean
![Page 13: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/13.jpg)
Oceanic Crust:
• Forms the deep sea floor
• 5 - 10 km thick (average ~ 7 km)
• Basalt (Fe / Mg / Al / Na / Ca / SiOx) = igneous rock
• Relatively dense (~ 3 g/cc) = negatively buoyant
• Surface averages ~ 4 km below sea level
• Young ( ≤ 160 - 190 million years old)
• Covers ~ 65% of earth’s surface
Continental crust Oceanic crust
Ocean
![Page 14: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/14.jpg)
• 70-250 km thick
• Thicker under continents
• Thinner under oceans
• Broken into many plates
• Lithospheric plates “float” on soft asthenosphere*
*Asthenosphere: From the Greek, asthenes = weak
Lithosphere = Crust + Solid Outer Mantle(from Greek: Lithos = rocky)
![Page 15: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/15.jpg)
![Page 16: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/16.jpg)
Tectonic Plates of the World
Source: Wikipedia http://en.wikipedia.org/wiki/Plate_tectonics
![Page 17: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/17.jpg)
Continental Drift: Continents have moved over the earth’s
surface during geological time.
• First proposed by German astronomer / meteorologist
Alfred Wegener circa 1910-12.• Highly controversial; ridiculed, esp. in U.S.• Finally accepted by mainstream geology in 1960s.
Alfred Wegener1880-1930
![Page 18: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/18.jpg)
Continental drift incorporated into modern theory of Plate Tectonics*:
*From the Greek: τεκτονικός "pertaining to building”
Scientific theory describing large scale movements of the Earth’s lithospheric plates
Drifting continents have had a major impact on the distribution and evolution of animals and plants over the past 200+ million years.
![Page 19: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/19.jpg)
Plate Tectonics and Oceanic Island Formation
(Highly simplified!)
![Page 20: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/20.jpg)
Convection Currents in Mantle Bring Molten Rock (Magma) Toward Lithosphere.
![Page 21: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/21.jpg)
Divergent Plate Boundary
• Magma pushes up from mantle through lithospheric plate• Forms new oceanic crust • Pushes plates apart (~5 cm / yr) = Sea Floor Spreading Center
Formation of Oceanic Crust Animation
http://www.wwnorton.com/college/geo/egeo/flash/2_7.swf
![Page 22: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/22.jpg)
Mid-ocean ridge system develops where sea-floor spreading occurs.
![Page 23: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/23.jpg)
Volcanic activity at mid-ocean ridge can form ocean islands (e.g., Iceland).
![Page 24: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/24.jpg)
Movement of lithospheric plate that includes continental crust results in continental drift.
Click Here to Play Seafloor Spreading Animation
http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf
![Page 25: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/25.jpg)
Movement of lithospheric plates caused breakup of Pangea Super-continent
~300 million years ago
http://sos.noaa.gov/videos/Scotese.mov
Click to play Animation
![Page 26: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/26.jpg)
Convergent Plate Boundary
Convergence of two oceanic plates: Denser plate sinks under lighter plate
= subduction zone.
Source: Wikipedia http://en.wikipedia.org/wiki/Plate_tectonics
![Page 27: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/27.jpg)
Click Here to Play Subduction Animation
http://www.wwnorton.com/college/geo/egeo/flash/2_9.swf
![Page 28: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/28.jpg)
Convergence of Crustal Plates withSubduction zone results in earthquake and volcanic
activity (e.g., Pacific Rim of Fire).
Source: Wikipedia http://en.wikipedia.org/wiki/Plate_tectonics
![Page 29: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/29.jpg)
Volcanic Activity at Tectonic Plate Boundaries
Source: USGS http://pubs.usgs.gov/gip/hawaii/page10.html
![Page 30: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/30.jpg)
Volcanic activity at subduction zone can form oceanic
islands (e.g., Aleutians; Lesser Antilles).
Source: Wikipedia http://en.wikipedia.org/wiki/File:Japan_separation.png
![Page 31: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/31.jpg)
In areas where lithospheric plate is thin, magma plume from mantle can push up through plate,
forming a “hot spot.”
Hotspot Volcano Animation
![Page 32: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/32.jpg)
Map of hot spots
http://www.math.montana.edu/~nmp/materials/ess/geosphere/advanced/activities/hotspots/index.html
![Page 33: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/33.jpg)
Hot spots under oceanic crust can form oceanic islands
![Page 34: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/34.jpg)
Review
Most oceanic islands formed by volcanic activity:
1. along mid-ocean ridge
2. along subduction zone at convergent boundary of two crustal plates
3. at “hot spot” in middle of crustal plate
![Page 35: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/35.jpg)
• Eventually, as volcanic island erodes and aging oceanic crust becomes more dense, volcanic cone submerges to form undersea mountain = seamount (rounded top) or guyot (flat top);
• Oceanic islands estimated to last only 5-10 million years.
![Page 36: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/36.jpg)
I. Geological Formation of Oceanic Islands
A. What is an oceanic island?B. Lithosphere and Plate Tectonics C. Formation of the Hawaiian Island Chain
![Page 37: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/37.jpg)
Hawaiian Islands
Source: USGS http://pubs.usgs.gov/gip/hawaii/page05.html
![Page 38: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/38.jpg)
Northwest Movement of Pacific Plate Over Fixed Hawaiian Hot Spot
Source: USGS http://pubs.usgs.gov/gip/hawaii/page12.html
![Page 39: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/39.jpg)
Ages of Hawaiian Islands
Source: http://volcano.und.edu/vwdocs/vwlessons/hotspots.html
![Page 40: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/40.jpg)
Hawaiian Island -Emperor Seamount Chain
Emperor Seamount chain extends north from Hawaiian islands
![Page 41: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/41.jpg)
Conventional plate tectonic theory assumes that lithospheric plates move, while hotspots are stationary; as plate moves over hotspot, volcano goes inactive.
![Page 42: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/42.jpg)
However, recent evidence suggests that hotspots can move. Emperor Seamount chain may have formed by hotspot that moved south as Pacific plate moved northwest.
![Page 43: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/43.jpg)
I. Geological Formation of Oceanic Islands
A. What is an oceanic island?B. Lithosphere and Plate Tectonics C. Formation of the Hawaiian Island ChainD. Formation of Bermuda
![Page 44: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/44.jpg)
Geological Formation of Bermuda (1)
•110 Million Years Ago (MYA): Volcanoes along Mid-Atlantic Ridge;
•Seafloor spreading moved volcanic cones NW at 2 cm/year;
• 30-50 MYA: Second phase of volcanic activity – probably due to hotspot -three volcanic cones formed Bermuda Rise.
•Bermuda Rise continued to migrate NW;
•One volcanic cone emerged above sea level (= 1,000 meter high mountain?);
![Page 45: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/45.jpg)
Geological Formation of Bermuda (2)
• 30 MY to present: Bermuda Rise continued moving to present location, 32° 10-30’N ~ 1000 km east-southeast of Cape Hatteras, NC ~ 1000 km southeast of Connecticut coast
•Bermuda Rise comprises three seamounts (relicts of volcanic cones): Argus Bank, Challenger Bank, and Bermuda Seamount (= Bermuda Pedestal);
![Page 46: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/46.jpg)
Bermuda Sea Mount
San SalvadorBahama Banks
Mid
-Atla
ntic
Rid
ge
http
://to
pex.
ucsd
.edu
/mar
ine_
topo
/gif
_top
o_tr
ack/
topo
8.gi
f
![Page 47: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/47.jpg)
Bermuda Rise
http://hoopermuseum.earthsci.carleton.ca/Bermuda/Geology/BERM5-1A.HTML
![Page 48: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/48.jpg)
Geological Formation of Bermuda (3)
• Top of Bermuda Seamount exposed (eroded) and submerged several times with rising and falling sea levels;
• Seamount capped with limestone precipitated from seawater (oolitic* limestone) and laid down by corals and other marine organisms (biogenic limestone) while submerged.
*Oolitic: “Egg-stone”- formed from ooids (spherical grains with
concentric layers; 0.25-2mm in diameter)
Ooids
![Page 49: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/49.jpg)
Satellite Image of Bermuda
Source: http://earthobservatory.nasa.gov/images/imagerecords/7000/7397/bermuda_l7_1999226_lrg.jpg
![Page 50: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/50.jpg)
Geological Formation of Bermuda (4)
•Coral reefs form rim around the Bermuda Platform.
•Islands of Bermuda are primarily “fossilized” sand dunes (aeolian* limestone) rising above limestone platform.
*Aeolian: Wind-blown (From Aeolus, the Greek God of Wind)
Reference: The Geology of Bermuda (Bermuda Zoological Society, GEO-01, 2006)
http://www.gov.bm/portal/server.pt/gateway/PTARGS_0_2_11280_207_227543_43/http%3B/ptpublisher.gov.bm%3B7087/publishedcontent/publish/new_min_of_environment/environmental_protection___project_nature_fact_sheets/the_geology_of_bermuda_0.pdf
![Page 51: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/51.jpg)
I. Geological Formation of Oceanic Islands
A. What is an oceanic island?B. Lithosphere and Plate Tectonics C. Formation of the Hawaiian Island ChainD. Formation of BermudaE. Formation of the Bahamas
![Page 52: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/52.jpg)
200 MYA: Pangea Pulls Apart• Atlantic Ocean
forms• Stretches margin
of continental crust• Warm, shallow
seas form over crustal platform
• CaCO3 precipitates – forms ooids
• Sediments accumulate at ~ 5 cm / 1000 years
• Ooids cemented together to form oolitic limestone
Gulf of Mexico
Caribbean Sea
South America
Africa
Tethys Trench
Mediterranean
N
Mid
-Atla
ntic
Rid
ge
fault
North America
![Page 53: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/53.jpg)
Bahamas Built on Limestone Platform
• Formed by precipitation of CaCO3 in warm, shallow seas over 120 MY• Ooids cemented together to form oolitic limestone• Continental crust subsided under weight of limestone• Cores to 6,100 meters (20,000 feet) are surface-cemented limestone!!• Crust NOT found in any cores to date
PeriodAge
present
35 my50 my
65 my
100 my
140 my
200 my
recent
EocenePalaeocene
LateCretaceous
EarlyCretaceous
Jurassic
Florida StraitsOf
Florida
CaySal Santeren
Channel
Andros
Tongue of the Ocean
Eleuthera
Atlantic Ocean
5000ft=1525m
10000ft=3050m
15000ft=4575m
20000ft=6100m
Pre-Jurassic
Crust?
![Page 54: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/54.jpg)
Bahamian Banks = Tops of Limestone Platform
• Channels cut through limestone platform (erosion; geological faults); • Deepest channel = Tongue of the Ocean (~ 3000 m deep)• Coral reefs formed around edges and on tops of platform• Inner lagoons accumulated sediments that formed banks and islands
PeriodAge
present
35 my50 my
65 my
100 my
140 my
200 my
recent
EocenePalaeocene
LateCretaceous
EarlyCretaceous
Jurassic
Florida StraitsOf
Florida
CaySal Santeren
Channel
Andros
Tongue of the Ocean
Eleuthera
Atlantic Ocean
5000ft=1525m
10000ft=3050m
15000ft=4575m
20000ft=6100m
Pre-Jurassic
Crust?
![Page 55: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/55.jpg)
Bahamas Banks
![Page 56: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/56.jpg)
Bucket Theory for Formation of Bahamian Bank
![Page 57: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/57.jpg)
LandSat Image of San Salvador Island
• San Salvador sits on isolated portion of Bahamas Platform
•Near-vertical wall of the platform drops off to depths of 2000-3000 meters (west) to 4000 meters (east).
![Page 58: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/58.jpg)
San Salvador Bank is rimmed by coral reef = “bucket” walls
Much of San Salvador’s terrestrial rock is “fossilized” sanddunes (aeolian* limestone) rising above limestone platform;
Some rock is ancient coral reef formed when sea level was higher.
San Salvador Island San Salvador Bank
![Page 59: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/59.jpg)
Bermuda and San Salvador:Similar processes at ocean surface
Very different geological origins
• Bermuda • San Salvador
![Page 60: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/60.jpg)
Is San Salvador an oceanic island?
•No evidence of direct, terrestrial connection to continent (now or in the past);
•Separated from continent by deep ocean.
![Page 61: I. Geological Formation of Oceanic Islands. A. What is an oceanic island?](https://reader036.fdocuments.us/reader036/viewer/2022062307/5515156755034673228b4ba1/html5/thumbnails/61.jpg)
End of Slide ShowMarch 28, 2011
Next Week:Corals and Coral Reefs