Volcanoes are also prodigious land builders as they have created the Hawaiian Island chain. Kilauea and Mauna Loa, two of the world's most active volcanoes, are still adding land to the island of Hawaii

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Volcanoes are also prodigious land builders as
they have created the Hawaiian Island chain.
Kilauea and Mauna Loa, two of the world's most
active volcanoes, are still adding land to the
island of Hawaii
Hawaii's Volcanoes Revealed
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Subduction of oceanic crust produces a Magma Plume
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Hawaiian volcanoes typically evolve in four
stages as volcanism waxes and wanes (1) early
alkalic, when volcanism originates on the deep
sea floor (2) shield, when roughly 95 percent
of a volcano's volume is emplaced (3)
post-shield alkalic, when small-volume eruptions
build scattered cones that thinly cap the
shield-stage lavas and (4) rejuvenated, when
lavas of distinct chemistry erupt following a
lengthy period of erosion and volcanic
quiescence. During the early alkalic and shield
stages, two or more elongate rift zones may
develop as flanks of the volcano separate.
Mantle-derived magma rises through a vertical
conduit and is temporarily stored in a shallow
summit reservoir from which magma may erupt
within the summit region or be injected laterally
into the rift zones. The ongoing activity at
Kilauea's Puu Oo cone that began in January
1983 is one such rift-zone eruption. The rift
zones commonly extend deep underwater, producing
submarine eruptions of bulbous pillow lava.
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Origin of the Hawaiian Isles Volcanism Hidden
deep beneath the Earth's surface on the Pacific
Oceans sea floor lie one of the most
constructive and yet least-understood natural
phenomena in the world Volcanoes of the
Hawaiian Island Chain. It extends for 2,400 km
(1,800 miles) from the extinct seamounts and
atolls in Northwestern Hawaiian Isles to active
volcanoes in southeast in Hawaiis Big Island.
The Pacific Oceanic plate is moving
northwesterly. Hawaiian volcanoes are formed by a
column of magma - molten rock - rising from deep
within the Earth on the seafloor, erupting on the
surface, and hardening in layers down the sides..
This forms the familiar shield shaped mountain we
associate with volcanoes. The mechanism is
termed as the Hotspot Volcanism, due to
convection in the Upper mantle. The hotspot on
the Pacific Oceanic Plate has been active for
past 43 million years. Hawaiian Volcanic Isles
are also flanked by the South Arch Volcanic field
and North Arch Volcanic Field. The Hotspot is not
fixed as new data reveals and the formation of
the islands is influenced by subduction of
shallow oceanic lithosphere. There are two
geologic trends of the Hawaiian volcanism,
Kea-Kilauea Trend and Loa- Loihi Trend.
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Life-cycle of Hawaiian hot spot volcanoes The
Hawaiian Islands volcanoes are the product of a
mantle hot spot in the middle of the Pacific
Plate. The hot spot's current activity is
underneath the southern end of the island of
Hawaii and the next volcano in the chain, Lo'ihi
Seamount, is forming on the sea floor just to the
south of Hawaii and should emerge in another
200,000 years. The volcanoes undergo a
progression of eruption styles and chemistries as
they age, from pre-shield stage (Lo'ihi), through
the major shield-building stage (Kilauea), to
post-shield (Haleakala) and rejuvenated stages
(such as Diamond Head on Oahu when it erupted).
As the enormous mountains build on top of the
ocean crust, the crust flexes downward and the
islands slowly sink. Erosion takes its toll on
the islands giant landslides have occurred off
all the islands, and some of the debris has
traveled hundreds of kilometers offshore. Most of
the Hawaiian Islands have irregular shapes, not
like the round volcanoes. This is because their
sides tend to collapse in gigantic landslides,
leaving chunks the size of cities scattered
around the deep sea floor near Hawaii. If such a
landslide happened today it would be devastating
to the islands and due to tsunamis Pacific Ring
of Fire
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Once a volcano has grown above sea level,
subaerial eruptions produce lava flows of jagged,
clinkery aa or smooth, ropy pahoehoe. If the
flows reach the ocean they are rapidly quenched
by seawater and shatter, producing a steep
blanket of unstable volcanic sediment that
mantles the upper submarine slopes. Above sea
level then, the volcanoes develop the classic
shield profile of gentle lava-flow slopes,
whereas below sea level slopes are substantially
steeper. While the volcanoes grow rapidly during
the shield stage, they may also collapse
catastrophically, generating giant landslides and
tsunami, or fail more gradually, forming slumps
on seafloor. Deformation and seismicity along
Kilauea's south flank indicate that slumping is
occurring there today. Loading of the underlying
Pacific Plate by the growing volcanic edifices
causes subsidence, forming deep basins at the
base of the volcanoes. Once volcanism wanes and
lava flows no longer reach the ocean, the volcano
continues to submerge, while erosion incises deep
river valleys, such as those on the Island of
Kauai. The edges of the submarine terraces that
ring the islands, mark paleocoastlines that are
now as much as 2,000 m underwater, many of which
are capped by drowned coral reefs.
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Direction Of Plate Movement
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This diagram shows the relative topography along
the Hawaiian chain. Note that with increasing age
to the NE, the volcanoes are eroded and sink
below sea level.
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The volcano grows by adding layer upon layer of
new pillow lava. Calderas are possible. Lava is
alkalic in composition, with highcontent of
sodium and potassium relative to the tholeiitic
basalts of the shield-building stage. It may or
may not emerge above
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Giant Landslides
Seamounts
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The large size of seafloor features, high
activity of volcanism, and rapid rates of
subsidence make the Hawaiian islands an ideal
place to study geologic processes.
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The Hawaiian islands sink into the ocean at a
measurable rate as the cessation of volcanism
that provides the magma to build the islands.
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Once extinct, the Hawaiian Islands continue to
erode until they slip below sea level. The
Emperor Seamount chain was once over the magma
plumeand probably looked much like the Hawaiian
Islands, but the volcanoes have since submerged.
The Pacific Plate is carrying the entire chain of
islands and seamounts to the north-north-west as
it drifts slowly to the Aleutian Trench and its
ultimate subduction.

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The Hawaiian Isles volcanoes undergo a
progression of eruption styles and chemistries as
they age, from pre-shield stage (e.g., Lo'ihi),
through the major shield-building stage (e.g.,
Kilauea), to post-shield (e.g., Haleakala) and
rejuvenated stages (such as Diamond Head on Oahu
when it erupted). As the enormous mountains build
on top of the ocean crust, the crust flexes
downward and the islands gradually sink,
sometimes rapidly (Mahukona). Erosion takes its
toll on the islands giant landslides have
occurred off all the islands, and some of the
debris has traveled hundreds of kilometers
offshore.  Once extinct, the islands continue to
erode until they slip below sea level. The
Pacific Plate is carrying the entire chain of
islands and seamounts to the north-north-west as
it drifts slowly to the Japan Trench and its
ultimate subduction.
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Collapsed lava pillow on Puna Ridge, the
submarine extension of Kilauea's East Rift Zone,
April 2001, MBARI.
Equivalent lava flow on land, on Kilauea's East
Rift Zone, April 2001
Observations of submarine lava flows indicate
volcanic processes that contradict conventional
wisdom. Discoveries of lava ponds and flood
basalts imply that lava may stay molten for a
long time, despite the almost infinite heat sink
of the ocean. Fragmental rocks-ash,
hyalo-clastites, and volcaniclastic rocks, limu o
Pele, and spatter imply that explosive eruptions
take place even in the deep sea, where
hydrostatic pressure is so great that steam
bubbles should not be able to expand
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This SPOT satellite image of the island of Oahu
reveals the extensive erosion that has removed
much of the material on the flanks of the Waianae
and Koolau volcanoes. Note the stream valleys
that reach the crest of the mountains. The
resistant rocks mark the location of the rift
zones of the volcanoes
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