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Dana stayed with missionary Titus Coan , who would provide decades of first-hand observations. Dana remained interested in the origin of the Hawaiian Islands, and directed a more in-depth study in and He confirmed that the islands' age increased with their distance from the southeastern-most island by observing differences in their degree of erosion. He also suggested that many other island chains in the Pacific showed a similar general increase in age from southeast to northwest. Dana concluded that the Hawaiian chain consisted of two volcanic strands, located along distinct but parallel curving pathways.
He coined the terms "Loa" and "Kea" for the two prominent trends. Dana proposed that the alignment of the Hawaiian Islands reflected localized volcanic activity along a major fissure zone. Dana's "great fissure" theory served as the working hypothesis for subsequent studies until the midth century.
Dana's work was followed up by geologist C. Dutton 's expedition, who refined and expanded Dana's ideas. Most notably, Dutton established that the island of Hawaii actually harbored five volcanoes, whereas Dana counted three. Stimulated by Dutton's expedition, Dana returned in , and published many accounts of his expedition in the American Journal of Science. In he published the most detailed manuscript of its day, and remained the definitive guide to Hawaiian volcanism for decades. The next century was a period of thorough investigation, marked by contributions from many top scientists.
Since that time, advances have enabled the study of previously limited areas of observation e.
In the s, the Hawaiian seafloor was mapped using ship-based sonar. These low seismic velocity zones often indicate hotter and more buoyant mantle material, consistent with a plume originating in the lower mantle and a pond of plume material in the upper mantle. The magma's original temperature was found in two ways, by testing garnet 's melting point in lava and by adjusting the lava for olivine deterioration. However, it has been shown that other plumes display highly variable surface heat fluxes and that this variability may be due to variable hydrothermal fluid flow in the Earth's crust above the hotspots.
This fluid flow advectively removes heat from the crust, and the measured conductive heat flow is therefore lower than the true total surface heat flux. Hawaiian volcanoes drift northwest from the hotspot at a rate of about 5—10 centimeters 2. Prior to the bend, the hotspot migrated an estimated 7 centimeters 2. The  expedition drilled six seamounts and tested the samples to determine their original latitude, and thus the characteristics and speed of the hotspot's drift pattern in total. Each successive volcano spends less time actively attached to the plume.
The large difference between the youngest and oldest lavas between Emperor and Hawaiian volcanoes indicates that the hotspot's velocity is increasing. For example, Kohala, the oldest volcano on Hawaii island, is one million years old and last erupted , years ago, a period of just under , years; whereas one of the oldest, Detroit Seamount, experienced 18 million or more years of volcanic activity.
The oldest volcano in the chain, Meiji Seamount, perched on the edge of the Aleutian Trench , formed 85 million years ago. It is unknown whether the seamount chain has been subducting under the Eurasian Plate, and whether the hotspot is older than Meiji Seamount, as any older seamounts have since been destroyed by the plate margin.
It is also possible that a collision near the Aleutian Trench had changed the velocity of the Pacific Plate, explaining the hotspot chain's bend; the relationship between these features is still being investigated. The composition of the volcanoes' magma has changed significantly according to analysis of the strontium — niobium — palladium elemental ratios. The Emperor Seamounts were active for at least 46 million years, with the oldest lava dated to the Cretaceous Period , followed by another 39 million years of activity along the Hawaiian segment of the chain, totaling 85 million years.
Data demonstrate vertical variability in the amount of strontium present in both the alkalic early stages and tholeitic later stages lavas. The systematic increase slows drastically at the time of the bend.
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Almost all magma created by the hotspot is igneous basalt ; the volcanoes are constructed almost entirely of this or the similar in composition but coarser-grained gabbro and diabase. Other igneous rocks such as nephelinite are present in small quantities; these occur often on the older volcanoes, most prominently Detroit Seamount. Hawaiian volcanoes are called "Hawaiian-type". Hawaiian lava spills out of craters and forms long streams of glowing molten rock, flowing down the slope, covering acres of land and replacing ocean with new land.
There is significant evidence that lava flow rates have been increasing. Over the last six million years they have been far higher than ever before, at over 0. The average for the last million years is even higher, at about 0. In comparison, the average production rate at a mid-ocean ridge is about 0. The rate along the Emperor seamount chain averaged about 0.
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The rate was almost zero for the initial five million or so years in the hotspot's life. The average lava production rate along the Hawaiian chain has been greater, at 0.
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The distance between individual volcanoes has shrunk. A detailed topographic analysis of the Hawaiian — Emperor seamount chain reveals the hotspot as the center of a topographic high, and that elevation falls with distance from the hotspot. The most rapid decrease in elevation and the highest ratio between the topography and geoid height are over the southeastern part of the chain, falling with distance from the hotspot, particularly at the intersection of the Molokai and Murray fracture zones. The most likely explanation is that the region between the two zones is more susceptible to reheating than most of the chain.
Another possible explanation is that the hotspot strength swells and subsides over time. In , Robert S. Dietz and his colleagues first identified the swell behavior. It was suggested that the cause was mantle upwelling.
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Later work pointed to tectonic uplift , caused by reheating within the lower lithosphere. However, normal seismic activity beneath the swell, as well as lack of detected heat flow, caused scientists to suggest dynamic topography as the cause, in which the motion of the hot and buoyant mantle plume supports the high surface topography around the islands. The Hawaii hotspot is a highly active seismic zone with thousands of earthquakes occurring on and near Hawaii island every year. Most are too small to be felt by people but some are large enough to result in minor to moderate devastation.
A tsunami claimed 46 more lives. Over its 85 million year history, the Hawaii hotspot has created at least volcanoes, more than of which are extinct volcanoes , seamounts , and atolls , four of which are active volcanoes , and two of which are dormant volcanoes. Hawaiian volcanoes are characterized by frequent rift eruptions , their large size thousands of cubic kilometers in volume , and their rough, decentralized shape. Rift zones are a prominent feature on these volcanoes, and account for their seemingly random volcanic structure.
The Hawaiian islands are carpeted by a large number of landslides sourced from volcanic collapse. These debris flows can be sorted into two broad categories: These slides have caused massive tsunamis and earthquakes, fractured volcanic massifs, and scattered debris hundreds of miles away from their source. Forced forward by the mass of newly ejected volcanic material, slumps may creep forward slowly, or surge forward in spasms that have caused the largest of Hawaii's historical earthquakes, in and Debris avalanches, meanwhile, are thinner and longer, and are defined by volcanic amphitheaters at their head and hummocky terrain at their base.
Evidence of these events exists in the form of marine deposits high on the slopes of many Hawaiian volcanoes,  and has marred the slopes of several Emperor seamounts, such as Daikakuji Guyot and Detroit Seamount. Hawaiian volcanoes follow a well-established life cycle of growth and erosion. After a new volcano forms, its lava output gradually increases.
Height and activity both peak when the volcano is around , years old and then rapidly decline. Eventually it goes dormant, and eventually extinct. Erosion then weathers the volcano until it again becomes a seamount. This life cycle consists of several stages. During this stage, the volcano builds height through increasingly frequent eruptions. The sea's pressure prevents explosive eruptions. The cold water quickly solidifies the lava, producing the pillow lava that is typical of underwater volcanic activity.
As the seamount slowly grows, it goes through the shield stages. It forms many mature features, such as a caldera , while submerged. The summit eventually breaches the surface, and the lava and ocean water "battle" for control as the volcano enters the explosive subphase. This stage of development is exemplified by explosive steam vents. This stage produces mostly volcanic ash , a result of the waves dampening the lava. The volcano enters the subaerial subphase once it is tall enough to escape the water.
Thereafter eruptions become much less explosive. Hawaiian lava is often runny, blocky, slow, and relatively easy to predict; the USGS tracks where it is most likely to run, and maintains a tourist site for viewing the lava. After the subaerial phase the volcano enters a series of postshield stages involving subsidence and erosion, becoming an atoll and eventually a seamount. From Wikipedia, the free encyclopedia. A volcanic hotspot located near the Hawaiian Islands, in the northern Pacific Ocean.
Hotspot geology , Hawaiian — Emperor seamount chain , and Evolution of Hawaiian volcanoes. Pele deity , Halemaumau Crater , and Hawaiian mythology. List of volcanoes in the Hawaiian — Emperor seamount chain.
Evolution of Hawaiian volcanoes. Volcanoes portal Hawaii portal Geology portal. United States Geological Survey.