THE LIFE AND TIMES OF A HAWAIIAN VOLCANO

Scott K. Rowland, University of Hawai‘i at Manoa-

O‘ahu consists of two elongate shield volcanoes, Wai‘anae and Ko‘olau

Wai‘anae

Ko‘olau

The “production line” model of Hawaiian volcano evolution...

--diagram by Chuck Blay & Robert Siemers

adapted from Peterson & Moore (1987)

Koko Rift, SE end of Ko‘olau Volcano, O‘ahu

N coast of E. Moloka‘i

from Moore (1964)

obvious cliffs

actual avalanchescarps

PYROCLASTIC ACTIVITY AND VENT STRUCTURES ON HAWAIIAN VOLCANOES

ERUPTION STYLES AND VENT FORMS

Expanding gas drives a lava fountain. The highest fountains in Hawai‘i are >500 m

Technically, the base of the fountain is where the gas becomes 75% by volume, and this is usually 10s to 100s of meters below the vent rim.

Pu‘u ‘O‘o scoria cone (in the early 1990s)--

Kupaianaha lava pond, Kilauea (1986-1992)- -

~20 m

Mauna Iki satellitic shield, Kilauea SW rift zone-

(Kapoho, 1960)

HYDROMAGMATIC ERUPTIONS

Koko Rift rejuvenation-stagevolcanism, Ko‘olau volcano,O‘ahu:

-most of these eruptions occurred off the shoreline at the time

-tuff cones, many nested and/or coalesced, resulted

“surge” deposits, from lateral, turbulent deposition

HAWAIIAN LAVA FLOWS

Scott K. Rowland, University of Hawai‘i at Manoa-

Lava flows: ‘a‘a and pahoehoe- -

From Hawaiian Dictionary by M.K. Puku‘i & S.H. Elbert

-‘a‘a: 1. To burn, blaze, glow; fire; staring, as eyes. Fig., angry, fury. Ua ‘a‘a ‘ia au i ke aloha (I burn with love). 2. stony, abounding with ‘a‘a lava.

--

pahoehoe: 1. Smooth, unbroken type of lava. 2. Satin. 3. to drive fish into a net by beating the paddles rhythmically against the canoe.

-

‘a‘a and pahoehoe flows on the north flank of Mauna Loa- -

~3 m

Wave-cut cliff section, Makapu‘u, O‘ahu

RIFT ZONES AND CALDERAS ON HAWAIIAN VOLCANOES

Scott K. Rowland, University of Hawai‘i at Manoa-

Topography of Mauna Loa’s SW rift zone (dark flows post-date 1778)

Rift zones have the form of broad topographic ridges, and are where flank eruptions occur

If an eruption is going to occur along a rift zone somewhere, magma has to get there from the magma chamber. It does this as a blade-shaped body of magma called a dike.

-Tracking the rock-breaking earthquakes allows geologists to determine that most dikes propagate at 1-2 km/hour.

-Harmonic tremor tells geologists that magma is continuing to flow underground. Next time you are near a large waterpipe, put your hand on it and you will feel harmonic tremor.

Solidified dikes are exposed by erosion on older Hawaiian volcanoes

Kilauea caldera:-

Complex caldera-boundary faults,and Halema‘uma‘u,(H) an intra-calderapit crater 1954

lava flow

H

Rift zones on O‘ahu are identified most easily by mapping dike swarms.

Wai‘anaerift zone axes and caldera

Ko‘olaurift zone axesand caldera

PAU

‘Olelo no‘eau involving lava (from M. K. Pukui; compiled by Ululani Makue)-

O ka la ko luna, o ka pahoehoe ko lalo. The sun above, the smooth lava below. Said of a journey in which the travelersuffers because of the heat of the sun above and because ofthe reflected heat from the lava below (i.e., a difficult trip).

--

Kīke ke ‘ala, uwe ka mamane. When the boulders clash, themamane tree weeps. Meaning that when two people fight, those that are dear to them suffer.

- - - --

PAU