Transcript Geology of Kauai

Kauai is the northernmost and geologically the oldest and
most complex of the main Hawaiian Islands. It is roughly
circular in shape and was formed by a single shield volcano.
Kauai is the fourth largest of the Main Hawaiian Islands.
Kauai has a mean diameter of 43 kiolmeter (26 miles) and an
area of 555 square miles (143,710 ha).
The highest peak, Waialeale reaches an elevation of 1540 m
(5,052 ft), followed by Kawaikini, at 1600 m (4160 ft).
Mountainous terrain occupies the north, west and central part
of the island. The gentle east and south slopes are cut by
shallow gulches. A narrow, gently sloping coastal plain skirts
the island, but is interrupted on the northwest side by a 25 km
(16 mile) stretch of precipitous cliffs (Na Pali) which rise
from the water's edge, and on the southeast by a the Hoary
Head Mountains which rise to elevations of about 748 m
(2,280 ft.) above sea level. Adjacent to the coastal plain are
Geology of Kaua‘i
• Kaua’i consists of perhaps a single shield volcano
formed 5 million years ago.
• Like the Ko’olau Volcano on O‘ahu, only has shield
stage and rejuvenation stage without the postcaldera alkalic cap
– Lacks well-defined rift zones like O‘ahu volcanoes
• This volcano has experienced significant faulting
and has the largest known caldera of any Hawaiian
volcano
• This volcano has also passed through the erosion
and coral reef growing stages
– Erosion also affected by faulting: Waimea Canyon
Kaua‘i Volcano, Shield Stage
• Shield-stage rocks are called the Waimea Canyon
Volcanic Series
– Na Pali Member (5.10 to 4.30 Ma)
• shield-forming rocks outside of the caldera
• thin, inclined flows
• tholeiitic basalt
– Olokele and Makaweli Members (4.16-3.6 Ma)
• fill the caldera and the Makaweli graben (normal falut-bounded
valley), respectively
• thick, flat-lying flows
• tholeiitic basalt, alkalic basalt, and hawaiite
– Haupu Member (unknown age)
• lavas filling a small caldera on the southeastern flank of the volcano
Kaua‘i Volcano, Rejuvenation Stage
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Called the Koloa Volcanic Series
Age: 2.3 to 1.0 Ma
~40 vents, spatter and cinder cones, and a tuff cone
Koloa lavas cover about half of the surface of the
eastern part of the island
– floor the Lihue Basin
• Interbedded with the Koloa Volcanic Series is the
Palikea Formation, consisting of conglomerates
and breccias, coarse sedimentary rocks produced
by mass wasting-style erosion
View of the Lihue depression from westerly direction
Waimea Canyon is 16 km
(10 miles) long, a mile wide
and 1,000 meter (3,600 feet)
deep, with a completely
different climate at the
bottom than at the top
Waimea Canyon
Na Pali is one of the most rapidly eroding shorelines
in Kauai. As the cliffs erode, the landscape creates
fantastic, vaulted valleys and snaking, hidden beaches
where the sea hungrily licks at the thousand-foot cliffs.
Na Pali is one of the most rapidly eroding shorelines
in the world. It's crumbling. But as it erodes, the
landscape creates fantastic, vaulted valleys and
snaking, hidden beaches where the sea hungrily licks
at the thousand-foot cliffs.
Sedimentary Rocks
• Extensive deposits of colluvium (mass
wasting deposits) and alluvium
(stream erosion deposits)
• Cemented sand dunes and beach rock
• Sediments can form coastal plains
ancient
sea cliff
coastal
plain
Geologically the oldest of the main eight Hawaiian Islands, the
northernmost island of Kaua'i has a total area of 1420 sq km
(552 sq mi). This island receives the most rainfall of the main
eight Hawaiian Islands, thus giving its nickname of the
Garden Isle. Kaua'i is surrounded on all sides by a fringing
reef, with a reef flat sometimes as wide as 1 km (0.6 mi). The
reef is under the influence of high wave energy due to the
island's geographic position.
2006 March 14 Flood: Rushing waters from breached Kaloko Reservoir on Kaua'i gouged out
large portions of Wailapa Stream Tuesday before entering Morita Reservoir, at left. Farmers, who
depend on water from the reservoir, want it to be preserved, if it can be safely maintained.
Geology of Ni‘ihau
• Lies off of main trend of Hawaiian
Islands, a “cross trend”
• A deeply eroded remnant of a shield
volcano fringed by a platform composed
of rejuvenation stage volcanic rocks
• Well-developed calcareous dune
deposits
Ni‘ihau Volcanic Rocks
• Shield Stage
– Paniau Volcanic Series, 5.5 to 4.8 Ma
– tholeiitic and olivine-rich basalts, dikes and lavas
• evolving towards alkalic postsheild stage?
– caldera and summit are gone, only a rift zone remains
• erosion? faulting?
• Rejuvenation Stage
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Ki‘eki‘e Volcanic Series, 2.2 to -0.3 Ma
9 vents, including Lehua Island
all are dry eruptions except for 2 tuff cones
produced lavas that cover a wave-cut terrace
• alkalic olivine basalt, not as low in silica as rejuvenation
stages on other islands
fault-modified stream erosion on a shield volcano
Iniki flooding reached >800 ft inland and >25 ft above sea level