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