Hawaiian Ridge (WNW- Trending Islands and Atolls) and the Emperor Seamounts (N- Trending Collection of Submaring Mountains (Seamounts)
Principal Islands of the State of Hawai‘i
Ni‘ihau, Kaua‘i and Ka‘ula O‘ahu Moloka‘i, Lna‘i, Kaho‘olawe, Maui Hawai‘i Island = Big Island
This map also shows the off-shore regions with “cooler” shades indicating deeper water Some islands are approximately circular
Others clearly consist of two main mountain ranges, e.g., Wai‘anae and Ko‘olau on O‘ahu East and West Moloka‘i East and West Maui Or even 5!
Each individual mountain is a separate volcano Some islands are clustered into groups, separated by channels ‘Alenuihh channel separates Big Island from Maui Nui Ka‘iwi channel between O‘ahu and Moloka‘i Kauai channel between O‘ahu and Kaua‘i Only Big Island has had eruptions in the last 200 years Hawaiian Swell – more than just volcanic peaks sticking out of the water Arch – broad feature ~350 km across; rises ~1 km above moat Moat (or deep) – axis ~100 km off shore; discontinuous at least to Gardner Pinnacles; more prominent on N. side of ridge Ridge – rises 4500-9200 m above surrounding seafloor. Islands sit astride the ridge. Origin of the Swell
The swell is partly a product of thermal expansion - From intrusion of hot material from below
Volcanic loading on a stiff plate And partly a product of flexure - Plate bends or flexes downward below the volcanic Volcanic loading load and upward away from on an elastic plate it. The main Hawaiian islands represent only the SE end of a long structure that includes both the Hawaiian Ridge (WNW- trending islands and atolls) and the Emperor Seamounts (N- trending collection of submaring mountains (seamounts)
The Hawaiian Swell is present over much of this length, although it is most evident around the SE end of the chain. Hawaiian Ridge – generally deepens to NW
Swell topography (from Wessel, 1993)
Best fit to observations Predicted depth for plate rejuvenated to 45 Ma beneath the hotspot Predicted from cooling plate model Estimate of bathymetry away from swell
Models do not predict effects of fracture zones Variation in depth with distance along Hawaiian Ridge
subsidence
Most volcanoes west of Maui have subsided at least 3 km! Origin of Atolls (Darwin, 1839) Paired Volcanoes and Volcanic Lineaments
It is possible to draw lines through volcano locations Paired Volcanoes and volcanic lineaments
-The curved loci shown are not the only way to connect the dots -Note left-stepping lineaments in Hawaiian Ridge and right- stepping lineaments in Emperor Seamounts
Figure from Clague and Dalrymple [1989], based on Jackson et al. [1972] Irregular volume distribution along the Hawaiian Ridge
Midway
Gardner Pinnacles Age Progression along the Hawaiian Ridge
Hawaiian legends Pele changed house. Arrived on O‘ahu at Kneana from Kaua‘i, left O‘ahu along Koko rift Pele resided for a time at Haleakal, now resides at Halema‘uma‘u Crater in Klauea
J. D. Dana, U. S. Exploring Note that extinction age is not the Expedition, 1849 same as age of formation
Age of Extinction Last known activity Oldest known (based on amt of erosion) rocks Mauna Loa 1984 A.D. ~ 300 Ka Haleakal ~ 400 yrs B.P. ~ 900 Ka Mauna Kea ~ 3500 yrs B.P. ~ 380 ka Ko‘olau ~ 100 ka ~ 2.9 Ma West Maui ~ 400 ka ~ 1.8 Ma Wai‘anae ~ 3 Ma ~ 4.0 Ma Kaua‘i ~ 1 Ma ~ 6.0 Ma Modern approaches involve radiometric dating, primarily using K-Ar
Age-distance plot from Clague and Dalrymple (1989). Overall slope = 86 mm/yr.
Age-distance plot from Wessel and Kroenke (2000). Overall slope = 77 mm/yr with much higher rates in the SE end of the chain What does it mean to have an age progression along the Hawaiian Ridge?
1. The Hawaiian-Emperor chain is the result of some regular process that has been fairly systematic for at least the last 80 m.y. 2. It is a kind of clock, i.e. if you know where you are, you know the age of the rocks under your feet. What is moving? What changed ~43 million years ago (the age of the Hawaiian- Emperor “bend”?