University Honors Program, UH 204D-002: Great Expeditions Spring 2013 Montana State University, Bozeman

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!

4. Ship’s draught (draft)

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”

6. Sail plan of a three-masted barque:

8. HMS Beagle

9. HMS Beagle: Straits of Magellan

10. HMS Beagle

11. HMS Beagle

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

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.

17. HMS 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.

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)

25. Eltanin

26. Glomar Challenger
Deep Sea Drilling Project – DSDP
1968 – 1983 (NSF funded)

27. JOIDES / Resolution
Joint
Oceanographic
Institutions
for
Deep Earth Sampling
ODP
Ocean
Drilling
Program

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

31. Alfred Wegener Institute
for Polar & Marine Research
http://www.awi.de/en/home/

32. Russian ship: Arctic coring expedition

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

35. Galápagos

37. 1684 Map
Ambrose Cowley
Waved Albatross
Galápagos
Marine Iguana

38. The Black Pearl

39. Isabela – SPOT Satellite

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

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

47. Morgan, 1972

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?

52. Professor Harry Hess
Princeton University

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

55. Progressive evolution:

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

58. World-Wide Distribution of Hotspots

59. Calculated absolute velocity vectors relative to fixed hot-spot frame

60. Bathymetry around the Galápagos
Galapagos Bathymetry by William Chadwick, University of Oregon

62. Isla Isabela

63. Seafloor Spreading
Nikon D70S

66. Ridge topography
Hydrothermal circulation

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

70. Fast Spreading
9-18 cm/yr
Intermediate
Spreading
5-9 cm/yr
Slow Spreading
1-5 cm/yr
“Rise”
Spreading rates versus topography

71. Ridge versus Rise

72. Fast Spreading--
Southern East Pacific
Rise from 13 to 23°S

73. Upper crustal structure of a fast spreading ridge
•Broad arch with small axial graben
•Melt lens beneath rise
•Broad low-velocity zone

74. East Pacific Ridge/Rise

75. Intermediate Spreading--Juan de Fuca Ridge near 48°N

76. Simplified view of a slow spreading ridge & axial graben
Discontinuous axial volcanic ridge

77. Slow Spreading--Mid Atlantic Ridge near 22°N

78. Transform faults

80. Seafloor Spreading Rates
• Pacific-Cocos spreading rate  137 mm/yr
• Pacific-Nazca spreading rate  135 mm/yr
• Galápagos Ridge spreading rate  41 mm/yr
• Galápagos tip  propagates westward at 66 mm/yr

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

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)

84. 120o
120o
120o
Plate APlate B
Plate C
Classic RRR

85. East African
Rift & Afar
Triangle
•Gulf of Aden
•Red Sea
•East African rift

86. Afar Triangle

87. Mendocino
Rivera

88. Mendocino Triple Junction
Punta Gorda, CA

89. RRR Triple Junction

90. - Velocity Triangle Space -

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

96. Carnegie Ridge

97. Charles Darwin
(1809 – 1882)