The fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch 5,800 kilometres (3,600 mi) across the North Pacific Ocean, called the Hawaiian–Emperor seamount chain. Hawaiʻi's volcanoes rise an average of 4,572 metres (15,000 ft) to reach sea level from their base. The largest, Mauna Loa, is 4,169 metres (13,678 ft) high. As shield volcanoes, they are built by accumulated lava flows, growing a few meters or feet at a time to form a broad and gently sloping shape.
Hawaiian islands undergo a systematic pattern of submarine and subaerial growth that is followed by erosion. An island's stage of development reflects its distance from the Hawaii hotspot.
The Hawaiian–Emperor seamount chain is remarkable for its length and its number of volcanoes. The chain is split into two subsections across a break, separating the older Emperor Seamount Chain from the younger Hawaiian Ridge; the V-shaped bend of the chain is easily noticeable on maps.The volcanoes are progressively younger to the southeast; the oldest dated volcano, located at the northern end, is 81 million years old. The break between the two subchains is 43 million years; in comparison, the oldest of the principal islands, Kauaʻi, is little more than 5 million years.
The "assembly line" that forms the volcanoes is driven by a hotspot, a plume of magma deep within the Earth producing lava at the surface. As the Pacific Plate moves in a west-northwest direction, each volcano moves with it away from its place of origin above the hotspot. The age and location of the volcanoes are a record of the direction, rate of movement, and orientation of the Pacific Plate. The pronounced 43-million-year-old break separating the Hawaiian Ridge from the Emperor Chain marks a dramatic change in direction of plate movement.Initial, deeper-water volcanic eruptions are characterized by pillow lava, so named for their shape, while shallow-water eruptions tend to be composed mainly of volcanic ash. Once the volcano is high enough so as to eliminate interference from water, its lava flows become those of ropey pāhoehoe and blocky ʻAʻā lava.
Our current understanding of the process of evolution originates from the first half of the 20th century. The understanding of the process was advanced by frequent observation of volcanic eruptions, study of contrasting rock types, and reconnaissance mapping. More recently our understanding has been aided by geophysical studies, offshore submersible studies, the advent of radioactive dating, advances in petrology and geochemistry, advanced surveillance and monitoring, and detailed geological studies.The ratio of magnesium to silica in the lava is a sign of what stage the volcano is in, as over time the volcano's lavas shift from alkalic to tholeiitic lava, and then back to alkalic.
Although volcanism and erosion are the chief factors in the growth and erosion of a volcano, other factors are also involved. Subsidence is known to occur. Changes in sea level, occurring mostly during the Pleistocene, have caused drastic changes; an example is the breakup of Maui Nui, initially a seven-volcano island, which was transformed into five islands as a result of subsidence. High rainfall due to the trade wind effect impacts on the severity of erosion on many of the major volcanoes. Coastline collapses, a notable part of the history of many of the Hawaiian volcanoes, are often devastating and destroy large parts of the volcanoes.
When a volcano is created near the Hawaiian hotspot, it begins its growth in the submarine preshield stage, characterized by infrequent, typically low volume eruptions. The volcano is steep-sided, and it usually has a defined caldera and has two or more rift zones radiating from the summit. The type of lava erupted in this stage of activity is alkali basalt.Due to stretching forces, the development of two or more rift zones is common. The lava accumulates in a shallow magma storage reservoir.
Because the eruptions occur with the volcano underwater, the form of lava typically erupted is pillow lava. Pillow lava is rounded balls of lava that was given very little time to cool due to immediate exposure to water. Water pressure prevents the lava from exploding upon contact with the cold ocean water, forcing it to simmer and solidify quickly. This stage is thought to last about 200,000 years, but lavas erupted during this stage make up only a tiny fraction of the final volume of the volcano.As time progresses, eruptions become stronger and more frequent.
The only example of a Hawaiian volcano in this stage is Lō ʻ ihi Seamount, which is thought to be transitioning from the submarine preshield stage into the submarine phase of the shield stage. All older volcanoes have had their preshield stage lavas buried by younger lavas, so everything that is known about this stage comes from research done on Lōʻ ihi Seamount.
The shield stage of the volcano is subdivided into three phases: the submarine, explosive, and subaerial. During this stage of growth, the volcano accumulates about 95 percent of its mass and it takes on the "shield" shape that shield volcanoes are named for. It is also the stage at which the volcano's eruptive frequency reaches its peak.
As eruptions become more and more frequent at the end of the preshield stage, the composition of the lava erupted from the Hawaiian volcano changes from alkalic basalt to tholeiitic basalt and the volcano enters the submarine phase of the shield stage. In this phase, the volcano continues to erupt pillow lava. Calderas form, fill, and reform at the volcano's summit and the rift zones remain prominent. The volcano builds its way up to sea level. The submarine phase ends when the volcano is only shallowly submerged.
The only example of a volcano in this stage is Lōʻ ihi Seamount, which is now transitioning into this phase from the preshield stage.
This volcanic phase, so named for the explosive reactions with lava that take place, begins when the volcano just breaches the surface. The pressure and instantaneous cooling of being underwater stops, replaced instead by contact with air. Lava and seawater make intermittent contact, resulting in a lot of steam. 1,000 metres (3,000 ft) above sea level) that the interaction between sea water and erupting lava fades away.The change in environment also engenders a change in lava type, and the lava from this stage is mostly fragmented into volcanic ash. These explosive eruptions continue intermittently for several hundred thousand years. Calderas continually develop and fill, and rift zones remain prominent. The phase ends when the volcano has sufficient mass and height (about
Once a volcano has added enough mass and height to end frequent contact with water, the sub aerial substage begins. During this stage of activity, the explosive eruptions become much less frequent and the nature of the eruptions become much more gentle. Lava flows are a combination of pāhoehoe and ʻaʻā.It is during this stage, that the low-profile "shield" shape of Hawaiian volcanoes is formed, named for the shape of a warrior's shield. Eruption rates and frequencies peak, and about 95% of the volcano's eventual volume forms during a period of roughly 500,000 years.
The lava erupted in this stage form flows of pāhoehoe or ʻaʻā. During this subaerial stage, the flanks of the growing volcanoes are unstable and as a result, large landslides may occur. At least 17 major landslides have occurred around the major Hawaiian islands. This stage is arguably the most well-studied, as all eruptions that occurred in the 20th century on the island of Hawaii were produced by volcanoes in this phase.
Mauna Loa and Kīlauea volcanoes are in this phase of activity.
As the volcano reaches the end of the shield stage, the volcano goes through another series of changes as it enters the postshield stage. The type of lava erupted changes from tholeiitic basalt back to alkalic basalt and eruptions become slightly more explosive.Results from the Hawaii Scientific Drilling Project confirm that the eruption rates of the postshield stage volcanoes started decreasing between 600 and 400 thousand years (ka) ago.
Eruptions in the postshield stage cap the volcano with a carapace of lava, containing low silica and high alkali contents, the reverse of the stage before it. Some Hawaiian volcanoes diverge from this, however. Lava is erupted as stocky, pasty ʻ aʻ a flows along with a lot of cinder. Caldera development stops, and the rift zones become more inactive. The new lava flows increase the slope grade, as the ʻ aʻā never reaches the base of the volcano. These lavas commonly fill and overflow the caldera. Eruption rate gradually decreases over a period of about 250,000 years, eventually stopping altogether as the volcano becomes dormant.
Mauna Kea, Hualālai, and Haleakalā volcanoes are in this stage of activity.
After the volcano becomes dormant, the forces of erosion gain control of the mountain. The volcano subsides into the oceanic crust due to its immense weight and loses elevation. Meanwhile, rain also erodes the volcano, creating deeply incised valleys. Coral reefs grow along the shoreline. The volcano becomes a skeleton of its former self.
Kohala, Māhukona, Lanaʻi, and Waiʻanae volcanoes are examples of volcanoes in this stage of development.
After a long period of dormancy and erosion of the surface, the volcano may become active again, entering a final stage of activity called the rejuvenated stage. During this stage, the volcano erupts small volumes of lava very infrequently. These eruptions are often spread out over several millions of years.The composition of the lavas erupted in this stage is usually alkalic. The stage commonly occurs between 0.6 and 2 million years after it has entered the weathering cycle.
Koʻolau Range, West Maui, and Kahoʻolawe volcanoes are examples of volcanoes in this stage of development. Note, however, that because in this stage eruptions are very infrequent (occurring thousands or even tens of thousands of years apart), erosion is still the primary factor controlling the volcano's development.
After the rejuvenated stage, the volcano is too far away from the hotspot to receive new magma, and therefore will never erupt again. The volcano continues to sink into the ocean and become deeply eroded, leading to infrequent but large collapses in its original structure. The volcano has no remaining magma in its chambers, and is truly dead.
West Molokaʻi, Waiʻaleʻale, and Niʻihau volcanoes are in this stage of development.
Eventually, erosion and subsidence break the volcano down to sea level. At this point, the volcano becomes an atoll, with a ring of coral and sand islands surrounding a lagoon. All the Hawaiian islands west of the Gardner Pinnacles in the Northwestern Hawaiian Islands are in this stage.
Atolls are the product of the growth of tropical marine organisms, so these islands are only found in warm tropical waters. Eventually, the Pacific Plate carries the volcanic atoll into waters too cold for these marine organisms to maintain a coral reef by growth.Volcanic islands located beyond the warm water temperature requirements of reef-building organisms become seamounts as they subside and are eroded away at the surface. An island that is located where the ocean water temperatures are just sufficiently warm for upward reef growth to keep pace with the rate of subsidence is said to be at the Darwin point. Islands in more northerly latitudes evolve towards seamounts or guyots; islands closer to the equator evolve towards atolls (see Kure Atoll).
After the reef dies, the volcano subsides or erodes below sea level and becomes a coral-capped seamount. These flat-topped seamounts are called guyots. Most, if not all, the volcanoes west of Kure Atoll as well as most, if not all, the volcanoes in the Emperor Seamount chain are guyots or seamounts.
Not all Hawaiian volcanoes go through all of these stages of activity. An example is Koʻolau Range on Oʻahu, which was prehistorically devastated by a cataclysmic landslide, never underwent the postshield stage and went dormant for hundreds of thousands of years after the shield stage before coming back to life. Some volcanoes never made it above sea level; there is no evidence to suggest that West Molokai went through the rejuvenated stage, while its younger neighbors, East Molokai and West Maui, have evidently done so. It is currently unknown what stage of development the submerged volcano of Penguin Bank is in.
In recent years research at other seamounts, for instance Jasper Seamount, has confirmed that the Hawaiian model applies to other seamounts as well.
A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's surface, and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".
A shield volcano is a type of volcano usually composed almost entirely of fluid lava flows. It is named for its low profile, resembling a warrior's shield lying on the ground. This is caused by the highly fluid lava erupted, which travels farther than lava erupted from a stratovolcano, and results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
Kīlauea is an active shield volcano in the Hawaiian Islands that last erupted between 1983 and 2018. Historically, Kīlauea is the most active of the five volcanoes that together form the island of Hawaiʻi. Located along the southeastern shore of the island, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago.
Lōʻihi Seamount is an active submarine volcano about 35 km (22 mi) off the southeast coast of the island of Hawaii. The top of the seamount is about 975 m (3,000 ft) below sea level. This seamount is on the flank of Mauna Loa, the largest shield volcano on Earth. Lōʻihi, meaning "long" in Hawaiian, is the newest volcano in the Hawaiian–Emperor seamount chain, a string of volcanoes that stretches about 6,200 km (3,900 mi) northwest of Lōʻihi. Unlike most active volcanoes in the Pacific Ocean that make up the active plate margins on the Pacific Ring of Fire, Lōʻihi and the other volcanoes of the Hawaiian–Emperor seamount chain are hotspot volcanoes and formed well away from the nearest plate boundary. Volcanoes in the Hawaiian Islands arise from the Hawaii hotspot, and as the youngest volcano in the chain, Lōʻihi is the only Hawaiian volcano in the deep submarine preshield stage of development.
The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, and the Emperor Seamounts: together they form a vast underwater mountain region of islands and intervening seamounts, atolls, shallows, banks and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The seamount chain, containing over 80 identified undersea volcanoes, stretches about 6,200 kilometres (3,900 mi) from the Aleutian Trench in the far northwest Pacific to the Loʻihi seamount, the youngest volcano in the chain, which lies about 35 kilometres (22 mi) southeast of the Island of Hawaiʻi.
Tweed Volcano is a partially eroded Early Miocene shield volcano located in northeastern New South Wales, which formed when this region of Australia passed over the East Australia hotspot around 23 million years ago. Mount Warning, Lamington Plateau and the Border Ranges between New South Wales and Queensland are among the remnants of this volcano that was originally over 100 kilometres (62 mi) in diameter and nearly twice the height of Mount Warning today, at 1,156 metres (3,793 ft). Despite its size, Tweed Volcano was not a supervolcano; other shield volcanoes - such as on Hawaii - are much larger. In the 23 million years since the volcano was active, erosion has been extensive, forming a large erosion caldera around the volcanic plug of Mount Warning. Its erosion caldera is the largest in the Southern Hemisphere.
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relatively gentle, low level eruption; it is so named because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very small amounts of volcanic ash are produced. This type of eruption occurs most often at hotspot volcanoes such as Kīlauea on Hawaii's big island and in Iceland, though it can occur near subduction zones and rift zones. Another example of Hawaiian eruptions occurred on the island of Surtsey in Iceland from 1964 to 1967, when molten lava flowed from the crater to the sea.
Limu o Pele or Pele's seaweed is a geological term for thin sheets and subsequently shattered flakes of brownish-green to near-colorless volcanic glass lava spatter, commonly resembling seaweed in appearance, that have been erupted from a volcano. Limu o Pele is formed when water is forced into and trapped inside lava, as when waves wash over the top of the exposed flows of the molten rock. The water boils and is instantly converted to steam, expanding to form bubbles within the lava. The lava rapidly cools and solidifies as the bubbles grow. The volcanic glass bubbles burst and are dispersed by the wind, showering flakes of glass downwind.
The East Australia hotspot is a volcanic hotspot that forces magma up at weak spots in the Indo-Australian Plate to form volcanoes in Eastern Australia. It does not produce a single chain of volcanoes like the Hawaiian Islands. Unlike most hotspots, the East Australia hotspot has explosive eruptions, as well as the runny lava flows of the Hawaii hotspot, the Iceland hotspot and the Réunion hotspot. The hotspot is explosive because basaltic magma interacts with groundwater in aquifers below the surface producing violent phreatomagmatic eruptions.
Several types of volcanic eruptions—during which lava, tephra, and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.
The geology of the Pacific Northwest includes the composition, structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.
The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.
Submarine eruptions are those volcano eruptions which take place beneath the surface of water. These occur at constructive margins, subduction zones and within tectonic plates due to hotspots. This eruption style is far more prevalent than subaerial activity. For example, it is believed that 70 to 80% of the Earth's magma output takes place at mid-ocean ridges.
The Samoa hotspot is a volcanic hotspot located in the south Pacific Ocean. The hotspot model describes a hot upwelling plume of magma through the Earth's crust as an explanation of how volcanic islands are formed. The hotspot idea came from J. Tuzo Wilson in 1963 based on the Hawaii volcanic island chain.
Nintoku Seamount or Nintoku Guyot is a seamount and guyot in the Hawaiian-Emperor seamount chain. It is a large, irregularly shaped volcano that last erupted 66 million years ago. Three lava flows have been sampled at Nintoku Seamount; the flows are almost all alkalic (subaerial) lava. It is 56.2 million years old.
The volcanology of Eastern Canada includes the hundreds of volcanic areas and extensive lava formations in Eastern Canada. The region's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Eastern Canada has very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Eastern Canada are Archean age greenstone belts containing a rare volcanic rock called komatiite.
South Arch volcanic field is an underwater volcanic field south of Hawaiʻi Island. It was active during the last 10,000 years, and covers an area of 35 by 50 kilometres at a depth of 4,950 metres (16,240 ft).
North Arch volcanic field is an underwater volcanic field north of Oahu, Hawaii. It covers an area of about 25,000 square kilometres (9,700 sq mi) and consists of large expanses of alkali basalt, basanite and nephelinite that form extensive lava flows and volcanic cones. Some lava flows are longer than 100 kilometres (62 mi).
The geology of the Canary Islands is dominated by volcanic rock. The volcanic history of the Canary Islands started about 80 million years ago and the Canary Islands region is still volcanically active. The most recent volcanic eruption on land occurred in 1971 and the most recent underwater eruption was in 2011-12.