The Full Wiki

Hawaii hotspot: Map

Advertisements
  
  
  

Wikipedia article:

Map showing all locations mentioned on Wikipedia article:



The Hawai i hotspot is a volcanic hotspot responsible for the creation of the Hawaiian Islands in the central Pacific Oceanmarker, and is one of the best known and most studied hotspots on Earth. While most volcanic activity occurs along the boundaries of tectonic plates, powered by the movement of the plates, hotspots can occur far from any geological boundaries, and require a completely different mechanism for maintaining volcanic activity.

Seafloor spreading pushes Hawai i's volcanoes northwest about a year. 30 million years ago the Kuremarker and Midway atollsmarker were located where the island of Hawai imarker is now. The oldest extant volcano in the chain, Meiji Seamountmarker, began to form 86 million years ago; however, the hotspot may be older, if subduction of tectonic plates on the margin between the Pacific and Eurasian plates destroyed the older volcanoes.

The Hawai i hotspot has created at least 129 volcanoes, arranged in an arc known as the Hawaiian–Emperor seamount chainmarker. More than 123 are extinct volcanoes, seamounts, and atolls, four are active volcanoes, and two are dormant volcanoes. Hawaiian volcanoes range in age from 300,000 to 86 million years, progressing from southeast to northwest. Most are heavily eroded. This chain includes the Hawaiian Ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atollmarker, and the Emperor seamounts, a linear region of islands, seamounts, atolls, shallows, banks, and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The chain stretches over from the Aleutian Trenchmarker in the far northwest Pacific to Lō hi Seamountmarker, the youngest volcano in the chain, lying about southeast of the Island of Hawai i.

A bend corresponding to rocks between 41 and 43 million years old sharply divides the Hawaiian and Emperor sections. The bend was thought to result from sudden plate movement, but recent studies credit movement of the hotspot itself.

Ancient Hawaiian fishermen were the first to notice the increasing age of the islands, based on differences in erosion. James Dwight Dana directed the earliest formal geological study, from 1880 to 1881, and first confirmed the relationship between age and location, again based on erosion. In 1912, geologist Thomas Jaggar founded the Hawaiian Volcano Observatorymarker, initiating continuous scientific volcano observance on the island of Hawai i. 1946 saw the completion of the model for the evolution of Hawaiian volcanoes. J. Tuzo Wilson proposed the hotspot theory in 1963, using Hawa i island chain data. In the 1970s, a continuous effort began mapping Hawai i's seafloor, to gain more information regarding the area's complex geology.

Hotspot theory

The Hawai i hotspot is unusual, given that the vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but the Hawaiian Islands are an exception, because the nearest plate boundary is more than from the main island. In 1963, Canadian geophysicist J. Tuzo Wilson proposed the hotspot theory to explain this anomaly.

Wilson's stationary hotspot theory

Wilson claimed that certain small, long lasting, exceptionally hot areas of magma are located under Earth's surface, providing localized heat and energy systems, known as thermal or mantle plumes, that sustain long-lasting surface volcanic activity. This "mid-plate volcanism" builds mountains that rise from the relatively featureless sea floor, called seamounts, which eventually rise above the surface, forming volcanic islands. The hotspot remains relatively stationary, as Earth's tectonic plates slide over it, carrying the volcanoes with them. When the magma supply is cut and the volcano becomes extinct, the island eventually erodes back below the waves as a seamount. Meanwhile, a new volcano forms over the hotspot repeating the process, this time forming a new island, continuing until the mantle plume collapses.

According to Wilson's hotspot theory, the volcanoes of the Hawaiian chain should be progressively older and increasingly eroded northwestward from the hotspot. New volcanic rock is constantly being made at Hawai i's main island. The oldest rocks in the main Hawaiian islands, the rocks on Kaua imarker, are about 5.5 million years old and deeply eroded. In contrast, the rocks of the "Big Islandmarker", and those of Loi hi, are under 0.7 million years old.
A diagram demonstrating the drift of the Earth's crust over the hotspot


This process of growth and later dormancy forms long chains of volcanic islands over many millions of years, and in the case of Hawai i, it has left a trail of volcanic islands and seamounts across the Pacific Ocean floor. The group of Hawaiian volcanoes are part of a larger chain, dubbed the Hawaiian–Emperor seamount chainmarker.

The chain's length, orientation and distance between volcanoes records the direction and speed of the Pacific Plate's movement. Approximately 40–50 million years ago, it is thought to have suddenly changed direction, because of the subduction of the spreading ridge separating the Pacific and Izanagi plates, and the initiation of subduction along much of the Pacific Plate's western boundary. The change in direction was recorded by an L-shaped bend in the seamount chain, easily visible in raised-relief maps. However, this part of the theory has recently been challenged, and the bend might be attributed to the movement of the hotspot itself.

Many geophysicists believe that hotspots originate from the interaction between Earth's deepest layer, the planetary core, and the overlying mantle (see also, structure of the Earth). This zone, about thick, develops a small bump that protrudes slightly into the mantle from the deeper core layer of the Earth. The bump transfers the intense heat from Earth's center into the adjacent mantle, heating it. Convection currents raise the heat a few centimeters a year, because of molten rock's high viscosity. Because it is hotter than the surrounding mantle, the heat continues to rise, but does not melt the often highly metamorphosed silicate rock surrounding it, which is resistant to heat. As the heat enters the less-resistant crust layer, it melts the rock, forming a mantle plume, from which the volcanoes get lava.

Arguments for the validity of the hotspot theory generally center on:

  • The steady age progression of the Hawaiian islands and other seamount chains.
  • Just south of the Hawaiian–Emperor chain, the Austral–Marshall Islands seamount chain shows a similar bend in the trail of the Macdonald hotspot.
  • Other proposed hotspots (the Marquesas, Society, Pitcairn, Samoa and Macdonald hotspots) within the Pacific Basinmarker, follow the same age-progressed trend from southeast to northwest, remaining in fixed relative positions.
  • Seismology studies of Hawaii seem to show increased temperatures down to the core–mantle boundary, suggesting evidence of a plume.
The Loa and Kea volcanic trends


Shallow hotspot theory

Another hotspot theory speculates that hotspots are born from shallow tectonic interactions between the lithosphere and asthenosphere. Because of shifting plate boundaries, the area around Hawaii was vastly different 70–100 million years ago, and there may have been a spreading ridge (the Pacific–Kula Ridge) in the area that disappeared in the early Tertiary period, about 65 million years ago. After changing plate dynamics moved the ridge away, the area may have established a continuing magma supply, thus forming a self-sustaining hotspot, possibly tapping into deeper mantle processes.

Moving hotspot theory

The most disputed element of the theory is whether or not hotspots are fixed relative to the overlying tectonic plates, and to each other. Drill samples, collected by scientists as far back as 1963, suggested that the hotspot was not immobile, and that it may have drifted over time, at a relatively rapid pace of about per year during the late Cretaceous and early Tertiary times (81-47 Mya). In 1987, Peter Molnar and Joann Stock found that the hotspot does move, at least relative to the Atlantic Ocean. However, this was believed to be a result of the relative motions of the North American and Pacific plates rather than the hotspot itself.

The Ocean Drilling Program (ODP) is an international research effort designed to study the world's seafloors. In 2001, ODP funded a two-month excursion aboard the research vessel JOIDES Resolution to collect lava samples from four submerged Emperor seamounts. The project drilled Detroitmarker, Nintokumarker, and Koko seamountsmarker, all of which are in the far northwest end of the chain, the oldest section.

In 2003, a study used those lava samples to test the hotspot theory's validity. The findings suggested that the bend was caused by the motion of the Hawaiian hotspot itself.


Lead scientist John Tarduno told National Geographicmarker:

The Emperor and Hawaiian chains differ in orientation by about 60°, and it has long been assumed that a major change in plate movement caused the bend; but new research suggests this did not occur. The change in direction was never recorded by magnetic declinations, fracture zone orientations or plate motion reconstruction. Also, a continental collision would not have been fast enough to have produced such a pronounced bend in the chain.

To test whether or not the bend was a result of a change in direction of the Pacific Plate, scientists analyzed the lava samples' geochemistry to determine where and when they formed. Age was determined by the radiometric dating of radioactive isotopes of potassium and argon. Researchers estimated that the volcanoes formed during a period 81 million to 45 million years ago. Tarduno and his team determined where the volcanoes formed by analyzing the rock for the magnetic mineral magnetite. While hot lava from a volcanic eruption cools, tiny grains within the magnetite align with the Earth's magnetic field, and lock in place once the rock solidifies. Researchers were able to verify the latitudes at which the volcanoes formed by measuring the grains' orientation within the magnetite. Paleomagnetists concluded that the Hawaiian hotspot had drifted southward sometime in its history.

The study indicated that 47 million years ago, the hotspot's southward motion greatly slowed, perhaps stopping.

Some groups that do not believe in plate tectonics (see also, flood geology) cited the new discovery as one of many pieces of evidence against the hotspot theory.

Crack and magma theory

The main alternative to the hotspot theory is the "crack and magma" theory, historically known as the "great fissure". Proponents postulate that cracks in the lithosphere are propagated by torsional stresses in, or stretching of, tectonic plates, which allows magma to leak from below. While a crack in the Earth's crust and magma leaking through it are both required to produce a volcano, the hotspot debate is over how and why the crack is produced. Norman H. Sleep, Professor of Geology at Stanford Universitymarker stated, "the [question] is whether the crack is a secondary feature or the primary one." Proponents also cite, as evidence against the hotspot theory, that most hotspots occur on young lithosphere (typically less than 30 million years old), which is thinner and weaker than older lithosphere.

Other challenges

Arguments against the hotspot theory's validity generally center on several issues which either have yet to be explained by the hotspot theory, or directly challenge the theory:


  • Age progressive volcanism can also occur along "leaky" transform faults.
  • The bend between the Hawaiian and Emperor chains occurs close to where the chain crosses the Mendocino Fracture Zone.
  • The possibility that the bend did not result from a change in direction of movement of the Pacific plate.
  • Mantle temperature is inconsistent.
  • Petrology has revealed the magma seems to originate from a very shallow chamber in the asthenosphere.
  • Geochemistry is ambiguous regarding the depth of the magma's origin.
  • Seismology has yet to conclusively detect the mantle plume.
  • The apparent absence of an oceanic plume head or oceanic plateau (a flood basalt province or other large igneous province) that should have formed with the initial stages of mantle plume eruption. Other proposed hotspots also lack a plume head, while others lack a trail of volcanic activity, possibly indicating mantle plumes which produce only one volcanic event.


  • The apparent absence of a heatflow anomaly (increased thinning and temperature of the lithosphere around the suspected hotspot). The lithosphere over a mantle plume is expected be thinner and hotter than the average for lithosphere of the same age elsewhere. An alternative model is that the plume head results from excess magma production rather than high temperatures. In the case of that model, no heatflow anomaly is expected.
  • Large variations in the volcanism of the Hawaii hotspot, which is also three times more active than any other proposed hotspot. No thermal model has explained how high flux rates can occur beneath thick plates. The standard model predicts a large initial rate that declines subsequently, the opposite of that observed along the Hawaiian chain.
  • The Emperor part of the chain (the oldest entities, especially Meiji Seamountmarker) ends near a bend in the Kuril–Kamchatka Trenchmarker, where the seamounts on the Pacific Plate will be subducting under the Eurasian Plate. , it is unknown whether the seamount chain has been subducting under the Eurasian Plate, and whether the hotspot is older than Meiji Seamount. A collision here may have provided a change in direction of the Pacific Plate, and created the bend in the Kuril–Kamchatka Trench. The relationship between these features is still being investigated.


History of study



Three of the earliest recorded observers of the volcanoes were the Scottish scientists Archibald Menzies in 1794, James Macrae in 1825, and David Douglas in 1834. Just reaching the summits proved daunting: Menzies took three attempts to ascend Manua Loa, and Douglas died on the slopes of Manua Kea. The United States Exploring Expedition spent several months studying the islands in 1840–1841. American geologist James Dwight Dana was on that expedition, but Lieutenant Charles Wilkes spent most of the time hauling a pendulum apparatus to the summit of Manua Loa to measure gravity. Dana stayed with missionary Titus Coan, who would provide decades of first-hand observations. Although the California Gold Rush became a focus of American geology for a time, Dana published a short paper in 1852.

Dana remained interested in the origin of the Hawaiian Islands, and directed a more in-depth study in 1880 and 1881. 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. The Kea trend includes the volcanoes of Kīlaueamarker, Mauna Keamarker, Kohalamarker, Haleakalāmarker, and West Maui. The Loa trend includes Loi hi, Mauna Loamarker, Hualālaimarker, Kaho olawemarker, Lāna imarker, and West Moloka imarker.

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 mid-20th century. His conclusions were based mostly on the fact that almost all of the Hawaiian volcanoes have two rift zones, but only one is usually active.

Dana's work was followed up by geologist C. E. Dutton's 1884 expedition, who refined and expanded Dana's ideas. Most notably, Dutton established that the the island of Hawai re actually harbored five volcanoes, whereas Dana counted three. Dana had originally regarded Kīlauea as a flank vent of Mauna Loa, and Kohala as part of Mauna Kea. Dutton also refined some of Dana's observations, and is credited with the naming of 'a'ā and pāhoehoe-type lavas, although Dana did previously notice a distinction. Stimulated by Dutton's expedition, Dana returned to the island in 1887, and published many accounts of his expedition in the American Journal of Science. In 1890 he published a manuscript that was the most detailed of its day, and remained the definitive guide to Hawaiian volcanism for decades. In 1909, two further large volumes were published, which extensively quoted from earlier works now out of circulation.

In 1912 the study of Hawaiian volcanism was advanced by the foundation of the Hawaiian Volcano Observatorymarker by geologist Thomas Jaggar. The facility was taken over in 1919 by the National Oceanic and Atmospheric Administration and in 1924 by the United States Geological Survey (USGS), which marked the start of continuous volcano observation on Hawai i island. The next century was a period of thorough investigation, hallmarked by contributions from many top scientists and spearheaded by the volcanic observatory. The complete model for the evolution of Hawaiian volcanoes was first formulated in 1946, by USGS geologist and hydrologist Harold T. Stearns. Since that time, advances have enabled the study of previously limited areas of observation (e.g. improved rock dating methods and submarine volcanic stages).

In the 1970s, the Hawaiian seafloor was mapped using sonar. More direct ship-based sonar data was compiled with math-based SYNBAPS (Synthetic Bathymetric Profiling System) data, with the ship-based bathymetrics carrying the most weight. In 1971, geologist W. Jason Morgan went to Hawai i and gathered evidence against Dana's theory, which was first challenged in 1967 by geologists Jack Oliver and B. Isaacs.

From 1994 to 1998 the Japan Marine Science and Technology Center, mapped Hawai i in detail and studied its ocean floor, making it one of the world's best-studied marine features. The project, a collaboration with the USGS and other scientific agencies, utilized manned submersibles, remotely operated underwater vehicles, dredge samplings, and core samples. The Simrad EM300 multibeam side-scanning sonar system collected bathymetry and backscatter data.

Characteristics

The immense size of the Hawaiian hotspot and its creations is just one of many fascinating aspects.

Size



The tallest mountain in the Hawaii chain, Mauna Kea, has raised itself to above mean sea level. If measured from its base on the seafloor, this would make Mauna Kea the world's tallest mountain, at , compared to for Mount Everestmarker (measured from sea level).
 Hawai i is also surrounded by a myriad of seamounts; however, they were found to be unconnected to the hotspot and its vulcanism. The amount of lava erupted from the hotspot is estimated to be approximately  , enough to cover Californiamarker with a lava about   thick.


Seven shield volcanoes created the island of Maui Nui. In Hawaiian, "Nui" means "great" or "large", and Mauimarker is the name of Hawai i's second largest island (which formed Maui Nui's backbone). At its maximum, about 1.2 million years ago, Maui Nui was in size, 50% larger than the present-day island of Hawai i. Sea levels were lower than today, when glaciation during an ice age removed much of the Earth's water from the ocean. The volcanoes slowly subsided into the crust and along with erosion, the "saddles" connecting the volcanoes eventually flooded, and 200,000 years ago it subsided completely, forming the islands Maui, Moloka imarker, Lāna imarker, and Kaho olawemarker. Penguin Bank is a former island lying west of Moloka i that completely submerged and now hosts a cap of coral. The water between these four islands is relatively shallow, about deep. Maui Nui's outer edges plummet quickly to the abyssal plain. A flank collapse along the steep slopes could produce massive landslides. One prior collapse removed much of the northern half of East Moloka i.

Movement

Hawaiian volcanoes drift northwest from the hotspot at a rate of about a year. The hotspot is known to have migrated south by about relative to the Emperor seamount chain. This conclusion is supported by magnetic studies of volcanic rock from Emperor seamounts, which suggested that these seamounts formed at higher latitudes than present-day Hawai i. Prior to the bend, the hotspot migrated an estimated per year; the rate of movement changed at the time of the bend to about per year. What we know about Hawaiian drift comes mostly from the Ocean Drilling Program. The 2001 expedition drilled 6 of the Emperor seamounts, and tested the magnetic samples to determine their original latitude, and thus the characteristics and speed of the hotspot's drift pattern in total.


The amount of time each volcano spends actively attached to the Hawaiian mantle plume has decreased. The large difference between the youngest and oldest lavas between Emperor and Hawaiian volcanoes provides evidence that the Hawai i hotspot migrated far slower then than it does today; for example, Kohala, the oldest volcano on Hawai i island) emerged from the sea 500,000 years ago, and last erupted 120,000 years ago, a period of only 380,000 years; in comparison to Detroit seamount's (second oldest in the chain) 18 million or more years of volcanic activity.

The oldest volcano in the chain, Meiji Seamount, perched on the edge of the Aleutian Trenchmarker, is believed to have formed 82 million years ago. The seamount will be destroyed within a few million years, at its current rate of motion, as the Pacific Plate slides under the Eurasian Plate. The existence of older seamounts that may have already been destroyed by subduction is currently, , disputed.

Topography and geoid

A detailed analysis of the topography and geoid of the Hawaiian–Emperor seamount chain reveals that while high near the hotspot, local elevation falls with distance, but most severely between the Murray and Moloka imarker fracture zones. Both geoid and topography rapidly decrease westward of the intersection with the Murray. 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 1953, Robert S. Dietz and his colleagues first identified the swell behavior. It was suggested that the cause was an upwelling of the mantle. 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 a dynamic reason. Understanding the Hawaiian swell has important implications for hotspot study, island formation, and inner Earth.

Eruption frequency and scale

There is significant evidence that the volcanoes' eruption rates have been increasing, because the distance between volcanoes on the arc shrink towards the southeastern and newer end. At the time of its formation, the hotspot produced widely spaced volcanoes, such as the distance between Meiji and Detroit Seamount. It was not uncommon for the separation to reach or even . In the most recent times, the hotspot has produced a large island (Hawai i) compounded from five volcanoes. The eruption rate along the Emperor seamount chain averaged about of lava per year. The eruption 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 per year.

The eruption rate has been increasing. Over the last six million years it has been far higher than ever before, at over per year. The average for the last one million years is even higher, at about . In comparison, the average production rate at a mid-ocean ridge is about for every of ridge.

Lava

The volcanoes' lava composition has changed significantly, according to analysis of the StrontiumNiobiumPalladium elemental ratio. Data collected from the Emperor seamounts represents 43 million years of activity, with the oldest seamount lava dated to the late Mesozoic Era (Cretaceous Period) and the youngest to the early Cenozoic Era (Paleogene Period). This leads to the modern day with the eruptions on Loi hi and Kīlauea, another 39 million years of activity, totaling 82 million years. Data demonstrate a large upward variation 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. The change is partially associated with the thinning of the local plate as the Hawai i hotspot and the Pacific Plate moved away from one another.



Almost all magma created by the hotspot is igneous basalt; Hawaiian volcanoes are constructed almost entirely of this or the similar coarse-grained gabbro and diabase. Rarely, there are different igneous rocks, such as nephelinite; these have been found often on the older volcanoes, most prominently Detroit Seamount. Most eruptions are runny because basaltic magma is more fluid than magmas typical in more explosive eruptions such as the andesitic magmas producing spectacular and dangerous eruptions around Pacific Basin margins. Volcanoes are classified into several eruptive categories, and the eruptions at Hawaiian volcanoes are called "Hawaiian-type" after the typical Hawaiian volcanic eruption. Hawaiian lava spills out of craters and forms long streams of glowing molten rock, which spills down the slope, covering acres of land and forming new land where before there was ocean. The low gas and silica content of the lava keeps it runny for long periods of time.

Hawaiian volcanoes produce predominantly two lava types, pāhoehoe and ʻaʻā. Pāhoehoe is a highly pliable, thin type of relatively fast-flowing lava. It can appear bulbous, fresh-looking, wrinkled, fibrous, or in some other shape depending on its temperature. ʻAʻā flow, however, is characterized by a jagged, ruffled appearance compared to the smooth-flowing pāhoehoe flows. It is slightly thicker the pāhoehoe, but can move faster on an incline. The top cools and forms an insulating, jagged shell on the flow in the form of large basalt chunks, which insulates the flow and keeps it moving. Occasionally pāhoehoe converts to ʻaʻā while it is cooling or degassing. In addition to the two types of lava, Hawaiian volcanoes produce unique volcanic forms, described below.

Indirect studies found that the magma chamber is located at about which matches the estimated depth of the Cretaceous Period rock in the lithosphere. This seeming coincidence may indicate that the lithosphere acts as a lid on melting by arresting the magma's ascent. The lava's original temperature was tested in two ways, by testing garnet's melting point in lava, and by adjusting the lava for olivine deterioration to find the temperature that best matches data. Both tests (carried out by scientists from the United States Geological Survey) seem to confirm the temperature at about . The olivine test also found that the temperature could not have been greater than for the olivine to have retained that amount of clinopyroxene. The second test agreed, putting the temperature range at to . In comparison, the estimated temperature for mid-ocean ridge basalt is about .

Eruption phenomena



Hawaiian eruptions can produce Pele's hair, which are brownish threads of volcanic glass with a diameter of less than , and may be as long as . The strands form when molten lava is overstretched; for example, when an ʻaʻā flow runs off a steep cliff. Pele's hair is often carried high into the air during eruptions. Wind can blow the glass threads tens of kilometers from their place of origin.

Pele's tears are small droplet-shaped bits of volcanic glass ejected from volcanoes, which form when small bits of molten lava cool exceptionally quickly. Pele's tears are often black in color, and sometimes form on the tips of Pele's hair.

Pele's seaweed are sheets of brownish volcanic glass that form when pāhoehoe lava pours into the ocean. Water may become trapped and begin to boil within the lava, creating steam-filled bubbles of lava. As the bubble cools and bursts, the walls shatter and form thin plates of glass which may resemble seaweed.

Sometimes, molten basaltic lava solidifies around trees, forming "lava trees". The tree is incinerated forming a mold inside the crust. Lava Tree State Monument is located southeast of Pahoamarker on Hawai i. It preserves molds that formed when a lava flow swept through a forested area in 1790. Tree molds often preserve both the shape and the structure of the tree. They are common in fluid and fast moving pāhoehoe flows, and occasionally found in blockier ʻaʻā flows. Sometimes, the lava drains away before it cools but after incinerating the tree, leaving a hole in the ground.

The eruption of Hawaiian basaltic lavas results in the lava flowing down the volcano's slope, creating its own channel (or reusing existing channels), developing both pāhoehoe and ʻaʻā lava flows. Over time lava levees can develop in pāhoehoe by overflowing the channels, while in ʻaʻā they are caused by moving lava into blocks. On Hawai i these channels can often surround a kipuka (Hawaiian for "island"), an island of mature vegetation surrounded by barren younger lava. Kipuka form when lava surrounds a particular raised area, leaving its ecosystem intact.


Cooling of the lavas in a channel with pāhoehoe can result in the creation of a lava tube. The surrounding rock acts as an insulator for the interior lava preventing it from crystallizing. The tube allows lava to travel far from the eruption center, and may allow the lava to flow at higher speeds; a 1984 flow through Mauna Loa was recorded at speeds of over . The tube features include a flat floor and splatter (marking the flow's high point); an example is the Thurston lava tube, part of Hawai i Volcanoes National Park. Inside the lava tubes, one may also occasionally find "lava stalactites". If the chamber refills with lava after it has drained, it may partially melt the roof of the tube (made up of pāhoehoe), and gravity does the rest. After the roof resolidifies, fragile lava stalactites cling to it. Unlike their mineral counterparts, lava stalactites do not grow after formation.

Other structures include: dome lava fountains, essentially a hemispheric upwelling of lava; lava lakes, which are large volumes of molten lava pooled in a crater or depression (the one at Kīlauea, Kupaianaha, is one of only five active lakes worldwide); some of the highest lava fountains on Earth; lava falls (or lava cascade), where lava spills over a cliff or a steep descent; and lava "skylights", which are holes in the roof of a lava tube or underground pools of lava.

Evolution of Hawaiian volcanoes

Lava skylight with lava stalactites


Hawaiian volcanoes follow a well-established life cycle of growth and erosion. After a new volcano forms, its eruption rate gradually increases, peaking in both height and volcanic activity around 500,000 years of age, and then rapidly declines. The volcano's activity level fades with time until it goes dormant, and eventually extinct. At that point, erosion become the strongest factor, weathering the volcano until it sinks back below the waves, becoming a seamount.

This life cycle consists of several stages. The first stage is the submarine preshield stage, currently occupied solely by Loi hi, the newest volcano. During this stage, the volcano starts building up height through increasingly frequent eruptions. The sea pressurizes the lava, preventing explosive eruptions (since Hawaiian volcanoes have typically runny lava that would not happen anyway). The cold water immediately contacts the lava, giving it extremely little time to solidify. For that reason, pillow lava is typical of underwater volcanic activity.

As the volcano slowly rises in height, it begins to go through the shield stages. The volcano forms many mature volcano features, such as a caldera, during the sub-surface part of the shield stage. The summit just breaches the surface, and a "battle" between the volcanic lava and ocean water begins, and the volcano enters the explosive subphase. This stage of development is exemplified by explosive vents of steam. The lava released during this stage is mostly volcanic ash, a result of the waves dampening the lava. This conflict between lava and sea reverberates in Hawaiian mythology.

The volcano next enters the subaerial subphase, once it is tall enough to end frequent contact with the water. During this stage the volcano enters its prime, when it puts on 95% of its height in a period of roughly 500,000 years. Thereafter eruptions become much less explosive and more gentle. The lava released in this stage often includes both pāhoehoe and ʻaʻā. The most impressive of the Hawaiian volcanoes, Mauna Loa and Kīlauea, are in this phase of activity. Because of the high growth rate, landslides are extremely common. Hawaiian lava is often runny, blocky, slow, and relatively easy to predict; the USGS tracks where lava will most likely run, and maintains a tourist site for viewing the lava. Kīlauea has erupted continuously for the last 26 years through Puʻu ʻŌʻōmarker, a minor volcanic cone happily for vulcanologists (who get to study the lava) and tourists (who get to see it in person) alike.

After the subaerial phase the volcano undergoes a series of postshield stages, during which erosion whittles it down. The volcano eventually sinks below the sea to become a seamount (or often a guyot) once more. Because of Hawai i's location near the equator, as the volcano disintegrates, it develops into an atoll. Once the Pacific Plate moves it out of the isotherm (the bounds of coral reef life), the reef mostly dies away, and the extinct volcano becomes one of an estimated 10,000 barren seamounts worldwide. Every seamount in the Emperor element of the chain is a dead volcano.

Hawaiian mythology



The possibility that the Hawaiian islands became older as one moved northwest was suspected by ancient Hawaiians long before any scientific studies were conducted. During their voyages, sea-faring Hawaiians noticed differences in erosion, soil formation, and vegetation, allowing them to deduce that the islands to the north (Ni ihaumarker and Kaua i) were older then those to the southeast (Maui and Hawai i). The idea was handed down the generations through the legend of Pele, the fiery Hawaiian Goddess of Volcanoes.

Pele was born to the female spirit Haumea, or Hina, who, like all of the Hawai i gods and goddesses, descended from the supreme beings, Papa, or Earth Mother, and Wakea, or Sky Father. According to the myth, Pele originally lived on Kaua i, when her older sister Nāmaka, the Goddess of the Sea, attacked her for seducing her husband, Pele fled southeast to the island of Oahu. When she was forced by Nāmaka to flee again, Pele moved southeast to Maui and finally to Hawai i, where she still lives in the Halemaumau Cratermarker at the summit of Kīlauea. There she was safe, as the slopes of the mighty volcano are so high that even Nāmaka's mighty waves cannot reach her. The mythical flight of Pele from Kaua i to Hawai i, which alludes to an eternal struggle between volcanic islands and ocean waves, is consistent with geologic evidence about the ages of the islands decreasing to the southeast, obtained centuries later by scientists using radiometric dating.

Volcanoes of the hotspot

The well-documented major volcanoes of the chain are listed below, in chronological order. The chain also includes many other less-documented volcanoes. The main island of Hawaii comprises five volcanoes, with another, Loi hi, offshore. Hawaii is surrounded by large swarms of less significant seamounts.

Hawaiian archipelago
Name Last Eruption Coordinates Age Notes
Big Islandmarker
Lō hi Seamountmarker 1996 (Active) > 400,000 Submarine volcano approximately southeast of Hawaii. It will eventually breach sea level and become the newest Hawaiian island.
Kīlaueamarker Erupting 300,000–600,000 years Kīlauea is currently the most active volcano on Earth.Puʻu ʻŌʻō, a cinder cone of Kīlauea, has been erupting continuously since January 3, 1983, making it the longest-lived rift-zone eruption of the last six centuries.
Mauna Loamarker 1984 (Active) ~1 million years Largest volcano on Earth.
Hualālaimarker 1801 (Dormant) > 300,000 years Lies more or less due west of the much taller Mauna Kea and Mauna Loa mountains.
Mauna Keamarker About 4460 BP (Dormant) ~ 375,000–1 million years World's tallest mountain if below-sea elevation is counted.
Kohalamarker About 120,000 BP (Extinct) ~ 430,000–1 million years Believed to be the oldest volcano that makes up Hawaii Island.
Māhukonamarker Submerged, having long since dissapeared into the sea.
Mauimarker
Haleakalāmarker 18th Century ~ 0.75–2 million years forms more than 75% of Maui.
West Maui ~ 1.32 million years Much eroded shield volcano which makes up the western quarter of Maui.
Kaho olawemarker
Kaho olawemarker > 1.03 million years Smallest of the 8 principal Hawaiian islands. Uninhabited.
Lāna imarker
Lāna imarker ~ 1.28 million years Sixth-largest island. The only town is Lānaʻi Citymarker, a small settlement.
Moloka imarker
East Moloka i ~ 1.76 million years Volcano is today only what remains of the southern half.
West Moloka i ~ 1.9 million years Northern half suffered a large collapse 1.5 million years ago.
Oahumarker
Koolau Range 2.7 million A fragmented remnant of the eastern or windward shield volcano which also suffered a large collapse sometime before the Moloka i collapse.
Wai anae Range 2.5 million BP 3.7–3.9 million years The eroded remains of a shield volcano that comprised the western half of the island.
Kaʻulamarker
Kaʻulamarker ~ 4 million years Tiny crescent-shaped barren island. Uninhabited but for divers & fishermen.
Ni ihaumarker
Ni ihaumarker ~4.9 million Smallest inhabited island. Formed from a side vent of Kaua i.
Kaua imarker
Kaua imarker >5 million Oldest and fourth largest of the main islands, and home to Mount Waialealemarker, one of the wettest areas on Earth in terms of precipitation.
Major Northwestern Hawaiian Islands
Name Stage Coordinates Age Notes
Nihoamarker Extinct Island 7.2 million ± 0.3 Small rocky island which supported a small population about 1000 CE; features over 80 cultural sites, including religious places, agricultural terraces, and burial caves.
Necker Islandmarker Extinct Island 10.3 million ± 0.4 Small deserted island with Hawaiian religious shrines and artifacts.
French Frigate Shoalsmarker Atoll 12 million Largest atoll in the northwestern Hawaiian islands.
Gardner Pinnacles Atoll Island 12.3 million ± 1.0 Two barren rock outcrops surrounded by a reef.
Maro Reefmarker Atoll Largest coral reef of the northwestern Hawaiian islands.
Laysanmarker Atoll Island 19.9 million ± 0.3 Originally named "Kauō" meaning egg, referring to its shape, and home to one of only five natural lakes in all of Hawaii.
Lisianski Islandmarker Atoll Island A small island surrounded by a huge coral reef nearly the size of Oahu. Named after a Russian navy captain whose ship ran aground there in 1805.
Pearl and Hermes Atollmarker Atoll Island 20.6 million ± 2.7 A collection of small, sandy islands, with a lagoon and coral reef. Named after two whaling ships which wrecked on the reef in 1822.
Midway Atollmarker Atoll Island 27.7 million ± 0.6 Consists of a ring-shaped barrier reef and two large islets. Named "midway" because of its strategic location in the center of the Pacific Ocean, and was the site of a key battle during World War II.
Kure Atollmarker Atoll Northern-most coral atoll in the world.
Emperor Seamountsmarker
Many are named after emperors or empresses of the Kufun dynasty of Japanese history.
Name Type Coordinates Age Notes
Hancock Seamount Unknown
Colahan Seamount 38.6 million ± 0.3
Abbott Seamount 38.7 million ± 0.9
Daikakujimarker Guyot 42.4 million ± 2.3 Also the name of a Japanese temple.
Kammu Guyot Unknown Named for former emperor of Japan Emperor Kammu.
Yuryakumarker Guyot 43.4 million ± 1.6 Named after former emperor of Japan Emperor Yūryaku.
Kimmei Seamount ~ 39.9–50 million years Named after former emperor of Japan Emperor Kimmei.
Kokomarker Guyot 48.1 million ± 0.8 Named after former emperor of Japan Emperor Kōkō.
Ojin Guyot 55.2 million ± 0.7 Named after former emperor of Japan Emperor Ōjin.
Jingu Guyot 55.4 million ± 0.9 Named after former empress of Japan Empress Jingū.
Nintokumarker Guyot 56.2 million ± 0.6 Named after former emperor of Japan Emperor Nintokumarker.
Yomei Guyot Unknown Named for former emperor of Japan Emperor Yomei.
Suiko Guyot 59.6 million ± 0.6 –64.7 million ± 1.1 Named after former empress of Japan Empress Suiko.
Detroitmarker Seamount 76–81 million years Well documented seamount, second oldest.
Meijimarker Seamount 81–86 million years Named after former emperor of Japan Emperor Meiji. Oldest known seamount.
Back to Top


See also



Notes

  1. Kious, W. Jacquelyne; Tilling, Robert I. [1996], p. " The long trail of the Hawaiian hotspot"
  2. Kious, W. Jacquelyne; Tilling, Robert I. [1996], p. " "Hotspots": Mantle thermal plumes"
  3. Peterson, Donald W.; Moore, Richard B. (1987). "Geologic history and evolution of geologic concepts. Island of Hawaii" Volcanism in Hawaii Decker, Robert W.; Wright, Thomas L.; Stauffer, Peter H., 149–190: pp. 154–155 (PDF pp. 172–173).
  4. Peterson, Donald W.; Moore, Richard B. : pp. 157 (PDF pp. 175).
  5. Clague, David A.; Dalrymple, G. Brent (1987). "Geologic evolution" Volcanism in Hawaii Decker, Robert W.; Wright, Thomas L.; Stauffer, Peter H., 5–55: pp. 23 (PDF pp. 41).
  6. Westervelt , pp. 8–11
  7. Westervelt , p. 63.
  8. pg. 41–43
  9. Duncan, R. A. and Clague, D. A. (1984) The earliest volcanism on the Hawaiian Ridge (abstract), EOS American Geophysical Union Transactions, volume 65, page 1076.
  10. Clague, D. A. and Dalrymple, G. B. (1989) Tectonics, geochronology, and origin of the Hawaiian-Emperor Chain in Winterer, E. L. et al. (editors) (1989) The Eastern Pacific Ocean and Hawaii, Boulder, Geological Society of America, page 199.


References



External links




Embed code:
Advertisements






Got something to say? Make a comment.
Your name
Your email address
Message