Geology of Molokai - University of Hawaii

Figure 1. Map of the main eight Hawaiian Islands. Some areas of known coral reef growth are
shown in pink. The arrow denotes the location of the island of Moloka'i.
Geology of Island of Moloka‘i
• Formed by two large shield volcanoes:
– West Moloka‘i Volcano
• Shield Stage, Lower Member, 1.8-1.5 Ma
– typical tholeiitic basalts
– no evidence for a caldera
• Postshield Stage, Upper Member, age unknown
– very small and thin
– alkalic basalt and hawaiite
– East Moloka‘i Volcano
• Shield Stage, Lower Member, 1.8-1.5 Ma
– typical tholeiitic basalts
• Postshield Stage, Upper Member, 1.5-1.3 Ma
– mugearite, an alkalic intermediate rock more silica-rich than hawaiite
• Rejuvenation Stage? Kalaupapa Member, 0.6-0.3 Ma
– alkalic basalt (not a very low silica lava like basanite)
• a large portion of this volcano has been removed by a giant submarine
Molokai - Landforms
Maui Nui emerged 1.2 million years ago
Molokai was a part of the Maui Nui ‘Big Maui’ 1.2 million years Pleistocene
Molokai Volcanic Island – Growth and life stages of two volcanoes
1.2-1 Ma
1.8-1.5 million years ago
1 Ma
500,000 years ago
800,00 years ago
Shield Volcano
The Friendly Isle of Moloka'i encompasses 673 sq km (260 sq mi),
making it the fifth largest of the main eight Hawaiian Islands. The north
and west coasts of the island have little coral growth due to impact from
northwest swell. However, protected from the southern swell waves by
the islands of Lana'i and Kaho'olowe, the south shore of Moloka'i boasts
the longest continuous fringing reef of the U.S. and its holdings.
Molokai’s roughly rectangular shape results from the coalescence of two
separate shield volcanoes: the 1.9 million year old West Moloka'i
Volcano, and the younger (appx. 1.75 million year old) East Moloka'i
Volcano (Figure 1). To the southwest is Penguin Bank, a submarine
platform lying at a depth of approximately 57 m (170 ft). It is suggested
that Penguin Bank is either an offshore extension of the West Moloka'i
rift zone, or a separate submerged shield volcano. Later in its life, the
northeastern portion of the West Moloka'i Volcano collapsed into the
ocean, leaving behind large slide scarps.
Lava from the younger East Moloka'i Volcano flowed across the
lowland of the Ho’olehua Saddle and terminated against the flank and
slide scarps of the West Moloka'i Volcano. Near the end of its active
volcanism, the northern flank of the East Moloka'i Volcano slid into the
ocean leaving behind the towering pali (cliffs) on the northeast coast of
the island (Figure 2).
East Molokai is the remnant of a great shield volcano shaped in map
view like the bottom half of an ellipse split along its major axis. The
bottom half or southern flank slopes gently to the sea in the typical
manner of shield volcanoes. However, the northern flank of the ellipse
has been truncated by great cliffs rising up to 900 meter (3,000 feet)
above sea level.
The cliffs of East Molokai's north shore are remnants of a much larger
shield volcano whose northern flank had subsided along faults and
disappeared beneath the sea. This submarine landslide, giant slump, is
termed as Wailua Slump.
The sea cliffs of Molokai's north shore were formed when the northern
third of the East Molokai Volcano suddenly collapsed and slid off into
the sea. This was a geological event of cataclysmic proportions-involving about 600 cubic miles of island falling along a 25-mile long
landslide that tumbled out as far as 120 miles offshore. The landslide
was so fast and powerful that the last 80 miles of its 120-mile run was
uphill, climbing 900 feet up from the Hawaiian Deep, the great
depression caused by the weight of the islands. Displacement of this
much material generated a 2,000-foot high tsunami that inundated the
rest of Molokai and the nearby island of Lanai. Scientists date this
geologic event at about 1,400,000 years ago.
Molokai Volcanic Island
East Molokai Shield Volcano - Life stages and landslides:
source of magma (and explanation) not clear
-extremely low degrees of partial melting (very alkalic)
-very small overall volume of volcano
-Molokai, Maui, Oahu Ko‘olau, Kaua‘i
Extent of the Wailau and Nuuanu Submarine Landslides. From Prodigious
Submarine Landslides on the Hawaiian Ridge. J.D. Moore, et al. 1989.
Kauhako Volcano
Kalaupapa Peninsula
Physiographic Map of East Molokai: The inner dotted line and black
areas mark the edge of the caldera. The outer dotted line depicts the
shoreline of East Molokai Volcano before the great Wailau
Landslide. From The Caldera of East Molokai Volcano, Hawaiian Islands. Holcomb and
Compton. 1985.
The Kalaupapa Peninsula, on the north central coast of Moloka'i, resulted
from more recent volcanic activity when the Kauhako Crater erupted
approximately 300,000 years ago. The Kalaupapa Peninsula is backed by
the towering pali on one side and storm-battered coasts on the remaining
sides. Its inaccessibility led to its being chosen by the Kingdom of
Hawai'i as a settlement for people afflicted with Hansen’s Disease
Bisecting the island, the broad Ho’olehua Saddle, composed of eroded
sediment of the East and West Moloka'i Volcanoes, forms a low-lying
coastal plain along the south shore. The southeastern edge of the island is
bordered by an alluvial plain constructed from a series of semicontiguous alluvial fans associated with upland gulches. Three of the
broader areas, formed at the base of the three major gulches of
Kaunakakai, Kawela, and Kamalo (Kamalo’o), have played important
roles in early human settlement of the southeast coastline.
The island of Molokai presents a high contrast in the distribution of its
water resources. Eastern Molokai with its more mountainous terrain has
substantial water resources; whereas, western Molokai, with its lower
elevation and relatively flat terrain, has a paucity of water
resources. This imbalance, coupled with low soil fertility and high
evaporation from the persistent northeast tradewinds, led to the
construction of a transbasin water diversion system in 1961 to bring
water from eastern to western Molokai.
Molokai is part of Maui County. Maui County also encompasses the
islands of Maui, Lanai and Kahoolawe. Molokai covers an area of about
260 square miles. The 1990 census population for Molokai was 4,319
(Kanaukakai, 2,658 and Kualapu'u, 1,661). The present population is
estimated to be about 7,000 and is predominantly rural. Kaunakakai,
located about midway along Molokai's south coast, is the island's major
population and commercial center. Small communities and rural
Hawaiian Homestead settlements are located in the central part of the
island. The more mountainous eastern half of the island remains
unpopulated, except for scattered residences and a few commercial
The deep loose soils, the presence of streams and springs, the low,
irregular shoreline, and the relative protection and resources of the broad
reef platform provided an inviting physical environment for early human
occupation in the southeastern coastal area. Early Hawaiians took
advantage of the natural system to develop a regime of coastal activities
duplicated nowhere else in Hawai’i.
Digital Elevation Model (DEM) of Moloka‘i and color-coded oblique view looking northwestward
• Shield volcano
• Broad shoal that has subsided 57m below sea
• Covered with carbonate bank
• Once connected to Moloka’i when Moloka’i
was a part of Maui Nui
• Submerged within the last 100,000 years
• Longest stretch of
white sand beach in
the state of Hawai’I
• Over 3 miles long and
300 feet wide
• Sand supplied from
mo’omomi sand
Molokai, a high volcanic island in the Hawaii Isles chain, is 62 km
(E–W) long and 13 km wide (N–S). Formed predominantly by two
volcanoes, East Molokai (1.8 million years old) and West Molokai (1.9
million years old). Molokai is the fifth-largest island in the main
Hawaiian Islands.
Created by the Hawaiian hotspot, Molokai is isolated from
tectonic influences associated with continental and plate boundaries.
Deformation of the lithosphere by volcanic loading at the hotspot,
however, induces some vertical motion among the main islands.
However, no evidence has documented conclusively whether Molokai
is stable, emerging, or submerging through time.
At roughly 21 N, 157 W, Molokai lies between Oahu and Maui and
is protected on the south shore by the most extensive coral–algal
fringing reef among the main Hawaiian Islands
Oblique closeup view of the seafloor looking west toward Pailolo Channel, between
Maui (on left) and Molokai (on right). The modern reef platform (A) is in red and
orange colors. The older drowned reef (B) is at 400 m depth. The drowned reef front
rises 30 m above the seafloor to the north. The scale across the bottom of the image is
7.8 km. The vertical exaggeration is 5x.
Figure 5. Landsat satellite image overlaid with the benthic habitat classification map of Moloka'i showing
the Dominant Structure/Substrate layer and the percentage of each class. U.S. Geological Survey
Open File Report 2005-1070 Version 1.0 Moloka'i Benthic Habitat Mapping By Susan A. Cochran-Marquez USGS Pacific
Moloka'i has sites with the best coral coverage in the main eight
Hawaiian Islands.
the spectacular north shore cliffs from Kalaupapa to the Halawa Valley,
East Molokai..
Moloka'i’s Coral Reef System
The fringing coral reef tract along Moloka'i’s south shore consists of
three distinct parts: 1) inner reef flat; 2) reef crest; and, 3) outer fore reef
(Figure 3). Sedimentation and natural processes vary significantly
between these environments. The inner reef flat, lying in shallow water
nearest the shoreline, is a relatively level, broad platform and the first to
be influenced by terrestrial sedimentation and runoff. The reef crest is the
zone where waves impinge and commonly break. Water depth is
extremely shallow over the reef crest (less than 1 m), and it is
occasionally exposed during very low tides.
The outer fore reef slopes seaward from the reef crest to depths of about
35 m (105 ft), and corals grow abundantly to depths of about 25 m (83
ft). From a depth of 14 m (45 ft) to 25 m (83 ft), the Moloka'i reef has a
typical spurand- groove morphology. Reef spurs (buttresses) are oriented
shore perpendicular and are separated by broad grooves (channels) which
transport sand offshore. Live coral grows on the spurs, and commonly in
the grooves as well; relief is on the order of 1 to 3 m (3.5 to 10 ft).
Figure 3. Schematic diagram (top) of typical fringing reef tract. Aerial
photograph (below) showing the approximate locations of the inner reef
flat, reef crest, and outer forereef on Moloka'i.
The North Shore Cliffs from the Kalawao scenic overlook in Kalaupapa National Historic Park.
March 6, 2008 : Mokapu rises to a
narrow ridge 360 feet above sea
level and supports some of the
best native coastal plant habitat in
Hawai'i, including 29 native plant
species An unprecedented
eradication project on the tiny islet
Mokapu off north Moloka'i is
making rats more scarce than the
rare native plants and seabirds on
which they feast.
Last month's aerial dropping of
rodenticide pellets on the 10-acre
state seabird sanctuary was the
first of its kind for Hawai'i's
offshore islands.
Near the Pelekunu Valley in May 1999, a major landslide occurred along
the North Shore Cliff.
Pelekunu Bay and Valley, Northeast Molokai.
Relict clumps of Brighamia rockii survive on sea cliffs inaccessible to goats.
On this rat-free sea stack along Molokai's north shore a relict Prichardia
palm forest still survives.
Pelekunu Stream
Lands within Kalaupapa NHP consist of the relatively flat Makanalua
peninsula, three interior valleys and the rim of the adjacent cliffs or
pali. The volcanic eruption that created the peninsula was a more recent
geological event than the formation of the island of Molokai. The small
shield volcano, Pu'u 'Uao, gave birth to the peninsula by forming the
Kalaupapa shield. This feature is the most recent evidence of volcanism
on Molokai, occurring in the late Pleistocene.
The rest of the park, more than half, is part of the main shield volcano of
the island of Molokai and geologically distinct from the peninsula. It is
comprised of the Wai'alie'a, Waihanau and Waikolu valleys and the
spectacular pali rising more than 2,000 feet above the peninsula.
Kalaupapa's pali is the westward extension of Molokai's north shore
cliffs which extend all the way to the island's eastern end. The sea cliffs
of the north shore of Molokai, because of their geological significance,
have been designated a national natural landmark.
Waikolu, the largest and easternmost of the three valleys within Kalaupapa, is similar in its geological,
biological, ecological and archeological resources to the other windward valleys to the east--Pelekunu,
Wailau, and Halawa. However, due to the long-term effects of transbasin diversions of its flow, the
biological and ecological values of the Waikolu Stream have been compromised. These diversions were
begun in 1961 and studies conducted since then estimate that they remove approximately 20 percent of the
Mean Sea Level Trend
1617760 Hilo, Hawaii
The mean sea level trend is 3.36 millimeters/year (1.10 feet/century)
with a standard error of 0.21 mm/yr based on monthly mean sea level
data from 1927 to 1999
Mean Sea Level Trend
1615680 Kahului, Hawaii
The mean sea level trend is 2.09 millimeters/year (0.69 feet/century)
with a standard error of 0.43 mm/yr based on monthly mean sea level data from 1954 to 1999.
Mean Sea Level Trend
1612340 Honolulu, Hawaii
The mean sea level trend is 1.5 millimeters/year (0.49 feet/century)
with a standard error of 0.14 mm/yr based on monthly mean sea level data from 1905 to 1999.
Mean Sea Level Trend
1611400 Nawiliwili, Hawaii
The mean sea level trend is 1.53 millimeters/year (0.50 feet/century)
with a standard error of 0.38 mm/yr based on monthly mean sea level data from 1954 to 1999.
Mean Sea Level Trend 1612480 Mokuoloe, Hawaii
The mean sea level trend is 1.12 millimeters/year (0.37 feet/century)
with a standard error of 0.46 mm/yr based on monthly mean sea level data from 1957 to 1999.
Tsunami deposits on Moloka'i (S. Cochran)
Much of the area surrounding Kaunakakai is built upon tsunami deposits,
possibly from the ancient tsunami generated by the collapse of the west
coast of the Big Island of Hawai'i 100,000 years ago (Hazlett and
Hyndman, 1996; Moore, 2000). Described as a coral-basalt breccia
conglomerate by Moore et al (1994), these rocks units crop out 30 to 70
m above present-day sea level, and contain sub-rounded to angular basalt
clasts and light-colored fragments of reef material.
Though not on a grand scale, the sea cliffs along Molokai's north shore
continue to move. In May of 1999, a major landslide occurred just east
of the Pelekunu Valley. Originating near the top of 2,500-foot high cliffs,
the avalanche carried enough rock and soil debris to spill out into the
ocean and create about six acres of new land.
In Hawaii, two general types of slope failures have been identified:
slumps and debris avalanches.
Slumps are slow moving, up to 25 miles wide and over six miles thick,
with transverse ridges and steep toes. Hilina Pali in Hawaii Volcanoes
National Park is an example of a slump in progress.
Debris avalanches are fast moving, long (more than 140 miles) rather
than wide and much thinner (.3 mile to 1.25 miles). They commonly
have well-defined amphitheaters at their head and hummocky terrain in
their lower part. Each debris avalanche is thought to represent a single
episode of catastrophic slope failure. The great sea cliffs of the north
shore of Molokai are the remnants of a colossal debris avalanche called
the Wailau slide.
Allen, J.A., 1998, Mangroves as alien species: the case of Hawai'i. Global Ecology and
Biography Letters. Vol. 7. 61-71.
Anderson, R.N., Bradshaw, B., and Marders, W.G., 1973, Moloka'i present
and future. Hawai'i Agricultural Experiment Station, Departmental Paper 17.
College of Tropical Agriculture, University of Hawai'i. 108 p.
Bryan Jr., E.H., 1954, The Hawaiian Chain. Bishop Museum Press, Honolulu,
HI. 71 p.
Clague, D.A., Holcomb, R.T., Sinton, J.M., Detrick, R.S., and Torresan, M.E.,
1990, Pliocene and Pleistocene alkalic flood basalts on the seafloor north
of the Hawaiian Islands. Earth and Planetary Science Letters. Vol. 98, No. 2. 175-191.
Cooke, G.P., 1949, Moolelo o Moloka’i: a ranch story of Moloka’i. Honolulu
Star-Bulletin Press, Honolulu, HI. 164 p.
DeLeon, D., 22 April 1990, Opponents meet at high noon to discuss public
access to beach at Puko’o lagoon. Maui News, A5.
deLoach, L.F., 1975, Land and people of Moloka’i: an overview. Unpublished
masters thesis, University of Hawai’i.
Fletcher III, C.H., Murray-Wallace, C.V., Glenn, C.R., Sherman, C.E., and
Popp, B., 1999, Late quaternary eolianite geochemistry, petrology, and
aminostratigraphy at Kaiehu Pt. (Mo’omomi) Moloka'i, Hawai'i. In Fletcher
III, C.H. (ed.), 1999, unpublished, Moloka'i fieldtrip guidebook for
participants of the Non-steady State of the Inner Shelf and Shoreline:
Coastal Change on the Time Scale of Decades to Millennia in the late
Quaternary, IGCP Scientific Conference 437, Hawai'i, USA, November 912, 1999. 15-41.
Glauberman, S., 11 October 1983, Molokaians seek beach right of way.
Honolulu Star-Bulletin, A8.
Hazlett, R.W., and Hyndman, D.W., 1996, Roadside geology of Hawai’i.
Mountain Press Publishing, Missoula, MT. 307 p. 48
Hearty, P.J., 1999, Whole-rock aminostratigraphy – a case study in Moloka'i,
Hawai'i. In Fletcher III, C.H. (ed.), 1999, unpublished, Moloka'i fieldtrip
guidebook for participants of the Non-steady State of the Inner Shelf and
Shoreline: Coastal Change on the Time Scale of Decades to Millennia in
the late Quaternary, IGCP Scientific Conference 437, Hawai'i, USA,
November 9-12, 1999. 5-14.
Henke, L.A., 1929, A survey of livestock in Hawai'i. University of Hawai’i,
Honolulu, HI. 82 p.
Jokiel, P.L., and Brown, E.K., 2000, unpublished. Field notes: south Moloka'i
coastline coral coverage survey along the 10 m isobath. 10 p.
Judd, J.P. IV, 1936, Puleoo: the story of Moloka'i. Porter Printing Co., Honolulu, HI. 28 p.
Keesing, F.M., 1936, Hawaiian homesteading on Moloka’i. University of
Hawai’i Publications, Honolulu, HI. Vol. 1, No. 3. 133 p.
Kepler, A.K., and Kepler, C.B., 1991, Majestic Molokai: a nature lover's guide.
Mutual Publishing, Honolulu. 144 p.
Menzies, A., 1920, Hawai’i nei 128 years ago. The New Freedom, Honolulu, HI. 1 map.
Moberly Jr., R., and Chamberlain, T.,1964, Hawaiian Beach Systems.
Hawai'i Institute of Geophysics, Honolulu, HI. 177 p.
Moberly Jr., R., Cox, D.C., Chamberlain, T., McCoy Jr., F.W., and Campbell,
J.F., 1965, Hawai'i’s shoreline; app. 1, Coastal geology of Hawai'i. Hawai'i
Moore, J.G., Bryan, W.B., and Ludwig, K.R., 1994, Chaotic deposition by a
giant wave, Moloka'i, Hawai'i. Geological Society of America Bulletin. Vol.
106. 962-967.
Moore, A.L., 2000, Landward fining in onshore gravel as evidence for a late
Pleistocene tsunami on Moloka'i, Hawai'i. Geology. Vol. 28, No. 3. 247250.
Pager, S., 1995, Hawai'i: off the beaten path. Globe Pequot Press, Old
Saybrook, CT. 288 p.
Tanji, E., 14 January 1999, Plan maps Moloka'i’s future. The Honolulu
Advertiser, B1.
U.S. Army Corps of Engineers, 1978, Kaunakakai Harbor, Moloka'i, Hawai’i:
restudy of an authorized project with environmental statement. 83 p.
U.S. Army Corps of Engineers, 2001, Design for enhancement of waveinduced
circulation at Kaunakakai Harbor, Moloka'i, Hawai'i. Technical
Report CHL-01-, U.S. Army Corps of Engineers Coastal Hydraulics
Laboratory, Vicksburg, MS. 45 p.
Wilkinson, C. (ed.), 2000, Status of Coral Reefs of the World: 2000. Australia
Institute of Marine Science web publication:
USGS Open-File Report 02-158
Moloka'i Fieldtrip Guidebook: selected aspects of the geology,
geography, and coral reefs of Moloka'I
Pelekunu Valley
Pelekunu Stream is a swift, rocky, perennial stream that begins as a set of plunging
streamlets at elevations near 120 m on the sheer northern face of the Molokai Crest. The
catchment takes the form of a giant bowl, ringed by peaks including Kaunuohua, Olokui
and Kamakou, the latter at 1515 m being the highest point on Molokai. The headwater
reaches are nearly vertical, with the stream profile making an abrupt transition to a more
moderate gradient at ca. 915 m elevation, which is interpreted as the head of the midreach.
From this elevation downstream to the mouth the channel exhibits a moderate but continuous gradient, with numerous riffles and small cascades, and thus retains a midreach character completely to its seaward terminus.
The extreme lower section of Pelekunu Valley consists of a vegetated debris fan,
laced by various stream channels that are continually cut off and reoccupied. These abandoned channels in many cases contain pools with weak flow that are fed by seepage
through the pore spaces in the coarse surrounding alluvium. At the mouth of the stream
the debris fan forms a transverse barrier of water-rounded rocks and cobbles, behind
which the stream pools to form a small pond before entering the sea via a small rapid. The
size of the terminal pond varies according to spates and other stream fluctuations, and at
certain times of year a black sand beach is also exposed seaward of the cobble bar that
impounds it.
Further upstream at the head of the debris fan the bed narrows and vertical walls of
coarse volcanic conglomerate occasionally confine the channel. The basic channel substrate throughout this terminal section consists of rounded cobbles averaging 20–40 cm
diameter, alternating with beds of coarse gravel. Except for the large pool at the mouth,
the stream profile is composed primarily of erosional zones formed by rapids and riffles.
In the first kilometer upstream from the mouth numerous streamlets and rheocrenes enter
from the east bank off the steep flanking wall of the Olokui massif, forming swampy areas
at the base of the eastern valley wall. To the west of the stream mouth is an extensive com-