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HOTSPOTS, TECTONICS AND THE EVOLUTION OF A HAWAIIAN VOLCANO
GG104, University of Hawai‘i at Mānoa
EARTH LAYERS
http://upload.wikimedia.org/wikipedia/commons/4/44/Earth_seafloor_crust_age_1996.gif
AGES OF OCEANIC LITHOSPHERE
SUBDUCTION ZONE SHOWING EARTHQUAKES (STARS) AND TEMPERATURE(PURPLE = COOLEST, RED = HOTTEST)
Map view of seismicity in the Tonga-Kermadec region. Colors indicate focal depth, with yellow being the deepest, cyan and blue intermediate, and red-brown the shallowest. Small grey triangles are volcanoes.
Pacific plate
Australianplate
Pacific plate
Samoa
Aotearoa
DIAGRAM SHOWING THE GENERATION OF MAGMA AT A SUBDUCTION ZONEVIA HYDRATION MELTING
http://www.lpi.usra.edu/science/kiefer/Research/convect1FS.gif
http://quake.mit.edu/hilstgroup/MantleConvection/f3300a.gif
NATURE|VOL 421 | 2 JANUARY 2003 |www.nature.com/naturehttp://www.higp.hawaii.edu/~cecily/plume.nature.pdf
DIAGRAM SHOWING HOW SEISMIC WAVES FROM DISTANT EARTHQUAKESPASS UPWARDS TO HAWAI‘I SEISMOMETERS. IF THEY DON’T PASS THROUGHHOT ROCK, THEY ARRIVE WHEN EXPECTED. IF THEY DO PASS THROUGHHOT ROCK (I.E., THE HOTSPOT) THEY ARE SLOWED AND ARRIVE LATE.
SEISMIC TOMOGRAPHY DATA SHOWING ANOMOLOUSSLOWING OF S-WAVES UNDER HAWAI‘I. THE INTER-PRETATION IS THAT THESE WAVES ARE SLOWED BY THEPRESENCE OF ANOMALOUSLY HOT ROCK (THE HOTSPOT)
Wolfe et al. (2008), Science vol. 326, pp. 1388-1390
Hotspots on Earth – either they can’t puncture continents,or continents avoid them
A "hotspot", as we know it, is an upward-moving cylinder of solid mantle material.
The material in the center movesthe fastest and therefore finds itselfout of equilibrium the most. In turn, it melts to the greatest degree. Volcanoes fed by this part erupt tholeiite basalt and erupt often.
The outer part moves the slowest andonly melts a little bit. Volcanoes fedby this region erupt alkalic basalt anderupt infrequently.
In reality, if the upwelling startsat the core-mantle boundary, thena "hotspot" is more than 10 timesas tall as it is wide.
A “HOTSPOT” IS PROBABLY MORE LIKE A “HOT COLUMN”
Mauna Loa, viewed from Kīlauea
Mauna Kea, viewed from Hilo airport.
Mauna Kea, viewed from Mauna Loa
solidified magma chamber
erupting magma makes thewhole journey w/o stopping
erupting lava has all it’soriginal gas content andhas cooled
Post-shield alkalic flows (thicker, weather to light grey)
Main-shield tholeiite flows(thinner, weather to red-brown)
East Moloka‘i, viewed fromthe north.
Old volcano surface
Early western geologists noticedthe color and thickness variations. Later geologists determined thatthere was a geochemical patternas well.
Wai‘anae Volcano, north side of Nānākuli Valley
Main-shield flows(thinner, weather to red-brown)
Post-shield alkalic flows (thicker, weather to light grey)
Slide by John Sinton
The “production line” model of Hawaiian volcano evolution...
H A W A I I A N R I D G EE M
P E
R O
R S
E A
M O
U N
T S
Hawaiian-Emperorbend (~48 Ma)
Hawai‘i(<1 Ma)
Kaua‘i(5-6 Ma)Pihemanu
(Midway)(~27 Ma)
Nintoku Seamount(~56 Ma)
Meiji Seamount(60-70 Ma)
Pūhāhonu (Gardner Pinnacles)(~13 Ma)
--diagram by Chuck Blay & Robert Siemers
adapted from Peterson & Moore (1987)
HAWAIIAN ISLANDS STAGES AND AGES Volcano Volcanic Stage
Shield Post-Shield Cap Rejuvenation
Puna .03 - 0 Kīlauea Pāhala Ash ~ .031 Hilina 0.1 - .031 Ka‘u 0.3 - 0 Mauna Loa Kahuku Nīnole 0.54 + .4 Hualālai Hualālai ? 0.013 - 1801 A. D. Mauna Kea Hamākua 0.38 - ? Laupāhoehoe ? - .004 Kohala Pololū 0.5 - 0.3 Hawī 0.26 - .06 E. Maui Honomanū 1.1 - 0.97 Kula
Hāna 0.93 - 0.15 .15-0.0002
W. Maui Wailuku 1.6 - 1.3 Honolua ~ 1.15 Lahaina 0.61 – 0.39 Kaho‘olawe L. Member ?? U. Member ~ 1.0 Lāna‘i Lāna‘i 1.5 - 1.2 E. Moloka‘i L. Member 1.8 - 1.5 U. Member 1.5 - 1.3 Kalaupapa ~ 0.33 W. Moloka‘i 1.9 - 1.7 Ko‘olau Ko‘olau 2.7 - 1.8 Honolulu 0.6 -.03? Wai‘anae Kamaile‘unu
Lualualei 3.55 -3.06 3.9 - 3.55
Kolekole Pālehua
2.98 -2.80 3.06 -2.98
Kaua‘i
Makaweli Olokele Haupu Napali
4.15 - 3.6 5.1 - 4.3
Koloa 2.6 - ~0.2
Ni‘ihau Paniau 5.5 - 4.8 Ki‘eki‘e 2.2 - 0.3
Not every volcano has every stage
Some volcanoes skip a stage
Some volcanoes die young
Names with ages listed under stages are the names of mapped geological units