Transcript A New Theory on the Formation of Hotspot

Ages and Life-cycle of Hawaiian volcanoes
MBARI’s high-resolution bathymetry of Hawaii first revealed the presence of
numerous flat-topped volcanoes on the seafloor around the islands
Water discoloration, sulfur odor,
possible boiling water, and possible
minor floating pumice were
observed 60 km NW of the tip of
Oahu on May 22, 1956. The depth
at this location is about 3000 m.
Water discoloration, sulfur odor,
possible boiling water, and
possible minor floating pumice
were observed 60 km NW of the
tip of Oahu on May 22, 1956.
The depth at this location is
about 3000 m.
The mantle source generating the Hawaiian Islands is
chemically heterogeneous from volcano to volcano as
is well documented in numerous studies. Moreover,
growing evidence suggests that the source also varies
over time within a single volcano
Smoky Gun or a Hotspot
A young man from a Chinese
ethnic minority performance
group breathes fire on the roof of
a building in Chongqing
Haleakala
Mauna Loa
Kilauea
Oahu
Maui Nui
Hawaii
is not fixed
Magma is created at the Mantle wedge
Cracks on
the Pacific
Ocean crust
The Honolulu Series of Volcanic Eruptions is Recent, 100, 000 years
old with 15 Tuff Cones in northeast and southwest perpendicular to
3 million year old KoolausVolcanoc Series. If the Hotspot has been
active over 500,000 years under the Big Island, 300 km away from
Oahu. Other younger volcanoes are present on Molokai and Maui.
Did the Hotspot wander to Oahu and other Islands at the same time?
NO FIXED HOTSPOT, it is migrating along with the Pacific Plate.
Shallow oceanic crust is recycled by Plate Subduction to make
Younger volcanoes such as Diamond Head on the older Isles.
Any satisfactory theory for Hawaiian volcanism must explain
(or rationalize) the:
change in migration direction of the melting locus at the
bend,
association of the great bend with the Mendocino fracture
zone,
change in migration rate at the bend,
apparent commencement of the volcanic chain near a ridge,
absence of a “plume head”,
large variations in magmatic production, and a current
magmatic rate about 3 times greater than the next most
productive hotspots,
absence of a significant heat flow anomaly,
absence of lithospheric thinning,
absence of a strong high-temperature signal in the erupted
basalts,
production of very large volumes of magma even though the depth to
the top of the melting column is exceptionally large compared with
MORs,
spatial and temporal variation in the composition of erupted lavas on a
variety of scales,
remote location of Hawaii, near the center of a very large plate,
location of the oldest end of the chain with respect to the “Pacific
pocket”,
unique rift zones,
paired Loa and Kea trends,
seismic whole-mantle mantle structure that is apparently normal
compared with the Pacific ocean elsewhere, and
occurrence of a bathymetric swell (a moat and “arch”) along the eastern
two-thirds of the Hawaiian chain and wrapping around its southeastern
end, with alkalic basaltic volcanism occurring at some places along it.
In conclusion, Hawaii is not fully explained by any current
hypothesis. It is impressive that a region of the Earth so
extensively studied for so many years, by so many Earth
scientists with so many techniques could remain so
intransigent to full understanding.
Many of the numerous features that are not yet fully
understood, and the parameters of alternative hypotheses, are
not currently being studied, but they offer exciting research
opportunities.
Rising magma and
Magma rises into
High pressure causes
volcanic gases exert
reservoir beneath
rocks to break,
pressure
volcano
triggering earthquakes
Earthquake activity beneath a volcano almost always increases before an
eruption because magma and volcanic gas must first force their way up
through shallow underground fractures and passageways.
Pacific Ocean:
The Pacific Ocean is the largest of the world's five oceans
Location: the body of water between the Southern Ocean, Asia, Australia
and the western hemisphere
Area: 155.6 million square km, or about 15 times the size of the US. The
Pacific Ocean covers about 28 per cent of the global surface - larger than
the total land area of the world
Terrain: the ocean floor in the eastern Pacific is dominated by the East
Pacific Rise, while the western Pacific is dissected by deep trenches,
including the Mariana Trench, which is the world's deepest place
Deepest point: Challenger Deep in the Mariana Trench - 11,022m
Hotspots
Lowman accepts the orthodox view that oceanic islands and seamounts in the Pacific
are the result of the Pacific plate moving over hotspots. This should give rise to a
systematic age progression along hotspot trails, but good age progressions are very
rare, and a large majority show little or no age progression. The Cook-Austral and
Marquesas chains, for example, are marked by gross violations of a simple age-distance
relationship and by extreme variations of isotopic signature, inconsistent with a single
volcanic source. The Hawaiian chain provides a more consistent age sequence, but
the recent renewed volcanism in the Island after a gap of a million years does not
support the ‘hotspot hypothesis’.
There is no systematic variation of heat flow across the Hawaiian swell, contradicting the
simple hotspot model (Keith, 1993). There is no smoking gun that is puffing up the
islands, contradicting the ‘hotspot hypothesis’ origin of the Hawaiian Island chain.
Hotspots are commonly attributed to "mantle plumes" rising from the core-mantle
boundary. Sheth (1999) showed that plume explanations are ad hoc, artificial, and
inadequate, and that plumes are not required by any geological evidence. A mantle
plume from a deep hotspot would broaden upward as a result of drag forces, and would
attain a surface width of several hundred kilometres, far beyond oceanic island
dimensions. It is therefore claimed that hotspot tracks are produced by plume tails – but
the problem of what has happened to ancient and modern plume heads remains
unsolved.
It is significant that many ocean island chains are found along fracture zones, and
flood basalt provinces are at orthogonal intersections of the fracture zones (Smoot,
1997). A credible alternative explanation is that hotspot tracks are produced by
propagating rifts, and delineate the stress field, not the displacement field, of the
lithosphere (Sheth, 1999). In surge tectonics, linear volcanic chains are believed to be
produced by magma surge channels in the lithosphere (Meyerhoff et al., 1996).
There is a major controversy among plate tectonicists as to how fast hotspots move
relative to one another; one group believes that hotspots move at 3 mm/yr or less,
whereas the other believes that hotspots move at 10-20 mm/yr or more. These
differences are partly the result of "plate reconstruction" uncertainties (Gordon, 1995;
Baksi, 1999
Giant blocks in the South Kona Landslide, Hawaii
James G. Moore, Wilfred B. Bryan, Melvin H. Beeson, and William R.
Normark
U. S. Geological Survey, Menlo Park, CA, United States
Geology; February 1995; v. 23; no. 2; p. 125-128
A large field of blocky sea-floor hills, up to 10 km long and 500 m high,
are gigantic slide blocks derived from the west flank of Mauna Loa
volcano on the island of Hawaii. These megablocks are embedded in
the toe of the South Kona landslide, which extends approximately 80
km seaward from the present coastline to depths of nearly 5 km. A 1015-km-wide belt of numerous, smaller, 1-3-km-long slide blocks
separates the area of giant blocks from two submarine benches at depths
of 2600 and 3700 m depth that terminate seaward 20 to 30 km from the
shoreline