Measures of Central Tendency: Mean, Median and Mode
Plate Tectonics & Geology of the Galapagos Archipelago
1. Plate Tectonics & Geology of the
Galápagos Archipelago
University Honors Program, UH 204D-002:
Great Expeditions Spring 2013
2. HMS Beagle
• HMS Beagle was a Cherokee-class 10-gun brig-sloop of the Royal
Navy
• She was launched on 11 May 1820 from the Woolwich Dockyard on
the River Thames, at a cost of £7,803 and named after the beagle
dog breed
• In July of that year she took part in a fleet review celebrating the
coronation of King George IV in which she was the first ship to sail
under the new London Bridge
• She was adapted as a survey barque (three or more masts) and
took part in three major surveying expeditions
• On the second survey voyage the young naturalist Charles Darwin
was on board, and his work would eventually make Beagle one of
the most famous ships in history
• 1870 – scrapped
3. Beagle: Vital Statistics
• 90.3-feet-long
• Beam 25-feet-wide
• Draught (draft) 12.5 feet
– Vertical distance from water line and bottom of the hull – keel
– Determines the minimum depth of water the vessel can safely
navigate, and the weight of cargo she can carry
• Tons burthen 235 bm; 242 for second voyage
• Initially outfitted as a 10-gun Brig
• 1825 re-rigged as a three-masted Barque (Bark) with
only 6-guns
• When she was in the Galapagos, she had 65 men on board
– very cramped living conditions!
5. Tons Burthen
• Builder's Old Measurement (BOM or bm) is the method of calculating the
cargo capacity of a ship used in England from approximately 1650 to 1849
• It estimated the “tonnage” of a ship based on length and maximum beam
• It is a volumetric measurement of cubic capacity and NOT of weight; it is
expressed in "tons burthen”
12. Beagle’s History
• First voyage (1826-1830)
– Hydrographic survey of Patagonia and Tierra del Fuego
• Second voyage (1831-1836) – Darwin’s voyage
– Extensive surveys in South America, returning via New
Zealand and Australia to England on 2 October 1836
• Third voyage (1837-1843)
– Survey large parts of the coast of Australia
• Final years
– In 1845 the Beagle was refitted as a static coastguard
watch vessel to control smuggling on the Essex coast in the
navigable waterways beyond the north bank of the
Thames Estuary
13. Second Voyage (1831-1836)
1. Fix the longitude of Rio de Janeiro, from
which all other distances would be measured
2. Make a hydrographic survey of the coast of
South America and other places visited
3. Make astronomical and tidal observations
4. Report on the geology, climate, natural
history, people and cultures of the places
visited Darwin’s arena
14. Voyage of the HMS Beagle
27 December 1831 to 2 October 1836
15.
16. A watercolour by HMS Beagle's draughtsman, Conrad
Martens. Painted during the survey of Tierra del
Fuego, it depicts native Fuegians hailing the Beagle.
21. Darwin’s Beagle Experience
(1831-1836)
• The Beagle set sail from England on December
27, 1831 when Darwin was 22 years old; he
would not see England again for almost five years
• Living quarters = one corner of the ship’s chart
room in the stern (“poop cabin”)
– 3 x 3.5m and 1.813m high (5.95 ft.)
– 250 books, wash stand, chest of drawers, instrument
cabinet, two hammocks, and a large central chart
table
– Shared the room with midshipman Philip Gidley King
and Ship’s Mate John Lort Stokes (who slept in a small
annex to the cabin)
22. Darwin’s Quarters: Chart Room
HMS Beagle, 1832. Interior layout memory sketch by Philip Gidley
King, midshipman during the second voyage, prepared in 1897.
23.
24. The C&GS Ship Pioneer passing under the Golden Gate Bridge. The first towed marine
magnetometer, which was invented at the Scripps Institution of Oceanography, was first
deployed on this ship beginning in August 1955. (NOAA Photo Library)
30. Integrated Ocean Drilling Program (IODP)
Scientific deep sea drilling vessel
Chikyu has set a new world record
by drilling down and obtaining rock
samples from deeper than 2,111
meters below the seafloor off the
Shimokita Peninsula of Japan
33. Galápagos Archipelago
• Spanish names:
– Archipiélago de Colón
– Islas de Colón
– Islas Galápagos
• Archipelago island group, island chain, cluster of islands, or a sea containing a large number of
scattered islands
• Derived from the Greek ἄρχι- – arkhi- ("chief") and πέλαγος – pélagos ("sea")
• Types of archipelagos:
– Continental fragments (tectonically rifted continental margins) – active margin
– Continental islands (“drowned” margins – Scotland) – passive margin
– Oceanic islands
• Volcanic arcs – subduction zones
• Island chains – Hawaiian Islands (hot spots)
• The Galápagos consists of 13 main islands, 3 smaller islands, and 107 rocks and islets
• Located at the confluence of three ocean currents, the Galápagos are a “melting pot” of marine species
34. Location
• 973 km (525 nmi; 605 mi) west of continental Ecuador
• 1°40'N–1°36'S, 89°16'–92°01'W
– Volcán Wolf and Volcán Ecuador on Isla Isabela lie directly on the equator
• The first crude navigation chart of the islands was made by the buccaneer
Ambrose Cowley in 1684 (??); he named the individual islands after some
of his fellow pirates, or after the British noblemen who helped the
privateer's cause
– English pirates pilfered Spanish galleons carrying gold and silver from South
America to Spain
• More recently, the Ecuadorian government gave most of the islands
Spanish names, but many biological researchers still use the older English
names because those were used by Darwin
43. Galápagos Geology
• The Galápagos Islands are:
– An active group of basaltic volcanoes
– Located near two seafloor spreading ridges
– Part of a west-ward propagating seafloor
spreading ridge
– Sitting on top of a mantle hotspot
– Site of the first discovery of seafloor hydrothermal
vents on a spreading ridge (“Black Smokers”)
44. Name Last Eruption
Darwin Island Extinct
Fernandina 2009
Ecuador (volcano) 1150
Wolf Island Extinct
Cerro Azul 2008
Wolf (volcano) 1982
Darwin (volcano) 1813
Alcedo 1993
Sierra Negra 2005
Santiago Island 1906
Pinta Island 1928
Marchena Island 1991
Santa Cruz Island Unknown
Floreana Island Extinct
Genovesa Island Unknown
San Cristóbal Island Unknown
45.
46. Geology Overview
• The islands are located at the Galápagos triple junction
• The archipelago is located on the north margin of the Nazca
Plate, which is moving ESE and diving under the South
American Plate at a rate of 2.5 inches (6.4 cm) per year
• It is also atop the Galápagos volcanic hotspot (mantle
plume)
• The islands have a volcanic legacy going back 10s of millions
of years
50. Seafloor Morphology
• Complex interplay of N-S trending structures associated with the
EPR and E-W trending structures associated with the Galápagos
Ridge
• EPR changes from fast spreading to intermediate spreading and
develops an axial rift valley
• Galápagos Ridge develops an axial graben that deepens
westward, reaching >4000m in the Hess Deep
• West of the Hess Deep there is no clear expression of the
Galápagos Ridge
– Gap of 25-km between the spreading centers
– Magmatic gap?
53. The first guyot - discovered by Harry Hess of Princeton University
(guy-ot [gee-o ])
54. Guyot
• (guy-ot [gee-o ])
• Flat-topped submarine seamount, the summit of which lies l000-2000 m below
the ocean surface
• Seamount is a mountain rising from the ocean seafloor that does not reach to the
water's surface (sea level) and thus is not an island
• The term “guyot” is named after Arnold Guyot (1807-1884), 19th century Swiss-
American geologist
Rodriguez Seamount/Guyot
56. Galápagos Hotspot
• Responsible for the creation of the Galápagos Islands
and three major aseismic ridges
– Carnegie Ridge
– Cocos Ridge
– Malpelso Ridge
• Hotspot is complicated by its proximity to the
Galápagos triple junction (i.e., relative motion of three
plates, not just simple divergent seafloor spreading)
• Unlike many hotspots, the magmatic system is
heterogeneous – evidence of four major reservoirs
feeding the hotspot
67. Black Smokers
• Hydrothermal vent fields at or near ridge crests
• Vent fluids = up to 400oC
• Fluid chemistry from different spreading centers is
remarkably similar despite big differences in
spreading rates
• vent fluids have equilibrated with greenschist
assemblage of minerals
• Metalliferous deposits are common
– Hot, acidic, sulfide-rich solutions
– Base metals are precipitated when vent fluids come in
contact with cold seawater
68. Galápagos Black Smokers
• The first warm springs to be found on the mid-ocean ridge were
discovered in 1977 on the Galápagos spreading center
• Astonishing communities of animals around them, but they were weakly-
flowing vents emitting room-temperature fluids into the frigid surrounding
bottom waters
• In 1979, scalding hot “black smokers” jetting from the seafloor were
discovered elsewhere on the global mid-ocean ridge system
• Since 1977, additional exploration of the eastern Galápagos spreading
center located a few more diffuse vents populated by animals, but did not
succeed in finding any black smokers; some workers suggest that the
influence of the Galápagos hotspot on the Galápagos spreading center
may inhibit formation of cracks required to provide deep, hot fluid
pathways for black smokers, making smokers rare and hard to find
81. Galápagos Triple Junction
• RRR triple junction that separates the Nazca, Cocos and
Pacific seafloor plates
• The fast-spreading East Pacific Rise trends N-S in this
region and continues without offset past the triple
junction
– Smooth topography across the rise
• Galápagos Ridge E-W trending and slow-spreading
– Separates the Cocos and Nazca plates, to the north and
south, respectively
– Rough, more faulted topography across the ridge
82.
83. Triple Junctions
• The Earth’s lithosphere comprises a mosaic of
interlocking plates
• There are several places on the planet where three
plates come together - these are called triple junctions
• Triple junctions mark the intersection of combinations
of:
– Rifts or ridges (spreading centers)
– Transform fault boundaries
– Convergent boundaries (subduction zones)
94. Galápagos Gore
• Intersection of EPR & GR V-
shaped, triangular, faulted region called the
Galápagos Gore
– “V” opens to the east
– Older crust in the east than the west based on
magnetic anomalies
– The Galápagos Ridge has propagated from east-to-
west as it developed