Haleakalā, or the East Maui Volcano, is a massive shield volcano that forms more than 75% of the Hawaiian Island of Maui. The western 25% of the island is formed by another volcano, Mauna Kahalawai referred to as the West Maui Mountains; the tallest peak of Haleakalā, at 10,023 feet, is Puʻu ʻUlaʻula. From the summit one looks down into a massive depression some 11.25 km across, 3.2 km wide, nearly 800 m deep. The surrounding walls are steep and the interior barren-looking with a scattering of volcanic cones. Early Hawaiians applied the name Haleakalā to the general mountain. Haleakalā is the name of a peak on the southwestern edge of Kaupō Gap. In Hawaiian folklore, the depression at the summit of Haleakalā was home to the grandmother of the demigod Māui. According to the legend, Māui's grandmother helped him capture the sun and force it to slow its journey across the sky in order to lengthen the day. According to the United States Geological Survey USGS Volcano Warning Scheme for the United States, the Volcano Alert Level for Haleakala as of August 2015 was "normal".
A Normal status is used to designate typical volcanic activity in a non-eruptive phase. Haleakala has produced numerous eruptions including in the last 500 years; this volcanic activity has been along two rift zones: east. These two rift zones together form an arc that extends from La Perouse Bay on the southwest, through the Haleakalā Crater, to Hāna to the east; the east rift zone continues under the ocean beyond the east coast of Maui as Haleakalā Ridge, making the combined rift zones one of the longest in the Hawaiian Islands chain. Until East Maui Volcano was thought to have last erupted around 1790, based on comparisons of maps made during the voyages of La Perouse and George Vancouver. Recent advanced dating tests, have shown that the last eruption was more to have been in the 17th century; these last flows from the southwest rift zone of Haleakalā make up the large lava deposits of the Ahihi Kina`u/La Perouse Bay area of South Maui. Contrary to popular belief, Haleakalā crater is not volcanic in origin, nor can it be called a caldera.
Scientists believe that Haleakalā's crater was formed when the headwalls of two large erosional valleys merged at the summit of the volcano. These valleys formed the two large gaps — Koʻolau on the north side and Kaupō on the south — on either side of the depression. Macdonald, Abbott, & Peterson state it this way: Haleakalā is far smaller than many volcanic craters. On the island of Hawaiʻi, lava-flow hazards are rated on a scale of one through nine with one being the zone of highest hazard and nine being the zone of lowest hazard. For example, the summits and rift zones of Kilauea and Mauna Loa volcanoes are rated Hazard Zone 1. Using this same scale, preliminary estimates of lava-flow hazard zones on Maui made in 1983 by the U. S. Geological Survey rated the summit and southwest rift zone of Haleakala as Hazard Zone 3; the steep, downslope areas of the Kanaio and Kahikinui ahupuaʻa and the area north of Hana are rated as Hazard Zone 4. Other areas of Haleakala are rated comparable to the lava-flow hazards of Mauna Kohala.
These high hazard estimates for Haleakala are based on the frequency of its eruptions. Haleakala has erupted three times in the last 900 years. By way of comparison, both Mauna Loa and Kilauea have erupted more than a dozen times each in the last 90 years. Hualalai has an eruption rate comparable to Haleakala. All of Hualalai is rated as Hazard Zone 4. However, the frequency of eruption of a volcano is only one of the criteria on which hazards are based; the other important criterion is the lava flow coverage rate. Using the preliminary dates for Haleakala flows, only 8.7 square miles of lava flows have been emplaced in the last 900 years. In comparison 43 square miles of Hualalai are covered with flows 900 years old or younger and 104 square miles on Kilauea and 85 square miles on Mauna Loa are covered by lavas less than 200 years old. Thus, Haleakala is a distant fourth in coverage rates. Surrounding and including the crater is Haleakalā National Park, a 30,183-acre park, of which 24,719 acres are wilderness.
The park includes the summit depression, Kipahulu Valley on the southeast, ʻOheʻo Gulch, extending to the shoreline in the Kipahulu area. From the summit, there are two main trails leading into Haleakalā: Sliding Sands Trail and Halemauʻu Trail; the temperature near the summit tends to vary between about 40 °F and 60 °F and given the thin air and the possibility of dehydration at that elevation, the walking trails can be more challenging than one might expect. This is aggravated by the fact; because of this, hikers are faced with a difficult return ascent after descending 2000 ft or more to the crater floor. Despite this, Haleakalā is popular with tourists and locals alike, who venture to its summit, or to the visitor center just below the summit, to view the sunrise. There is lodging in the form of a few simple cabins, though no gas is available in the park; because of the remarkable clarity and stillness of the air, its elevation (with atmospheric pressure of 71 kilopascal
A stratovolcano known as a composite volcano, is a conical volcano built up by many layers of hardened lava, tephra and ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas; the lava flowing from stratovolcanoes cools and hardens before spreading far, due to high viscosity. The magma forming this lava is felsic, having high-to-intermediate levels of silica, with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows have travelled as far as 15 km. Stratovolcanoes are sometimes called "composite volcanoes" because of their composite stratified structure built up from sequential outpourings of erupted materials, they are in contrast to the less common shield volcanoes. Two famous examples of stratovolcanoes are Krakatoa, known for its catastrophic eruption in 1883 and Vesuvius, whose eruption in AD79 caused destruction of Pompeii and Herculaneum in 79 AD.
Both eruptions claimed thousands of lives. In modern times, Mount St. Helens and Mount Pinatubo have erupted catastrophically, with lesser losses of lives; the possible existence of stratovolcanoes on other terrestrial bodies of the Solar System has not been conclusively demonstrated. The one feasible exception are the existence of some isolated massifs on Mars, for example the Zephyria Tholus. Stratovolcanoes are common at subduction zones, forming chains and clusters along plate tectonic boundaries where oceanic crust is drawn under continental crust or another oceanic plate; the magma forming stratovolcanoes rises when water trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust is released into mantle rock of the asthenosphere above the sinking oceanic slab. The release of water from hydrated minerals is termed "dewatering", occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths; the water freed from the rock lowers the melting point of the overlying mantle rock, which undergoes partial melting and rises due to its lighter density relative to the surrounding mantle rock, pools temporarily at the base of the lithosphere.
The magma rises through the crust, incorporating silica-rich crustal rock, leading to a final intermediate composition. When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. There, the low pressure allows water and other volatiles dissolved in the magma to escape from solution, as occurs when a bottle of carbonated water is opened, releasing CO2. Once a critical volume of magma and gas accumulates, the plug of the volcanic vent is broken, leading to a sudden explosive eruption. In recorded history, explosive eruptions at subduction zone volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, such as Mount St. Helens, Mount Etna and Mount Pinatubo erupt with explosive force: the magma is too stiff to allow easy escape of volcanic gases; as a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty magma. Following the breaching of the vent and the opening of the crater, the magma degasses explosively.
The magma and gases blast out with full force. Since 1600 CE, nearly 300,000 people have been killed by volcanic eruptions. Most deaths were caused by pyroclastic flows and lahars, deadly hazards that accompany explosive eruptions of subduction-zone stratovolcanoes. Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine ash, fragmented lava and superheated gases that can travel at speeds in excess of 160 km/h. Around 30,000 people were killed by pyroclastic flows during the 1902 eruption of Mount Pelée on the island of Martinique in the Caribbean. In March to April 1982, three explosive eruptions of El Chichón in the State of Chiapas in southeastern Mexico, caused the worst volcanic disaster in that country's history. Villages within 8 km of the volcano were destroyed by pyroclastic flows, killing more than 2,000 people. Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards. On June 15, Mount Pinatubo spewed an ash cloud 40 km into the air and produced huge pyroclastic surges and lahar floods that devastated a large area around the volcano.
Pinatubo, located in Central Luzon just 90 km west-northwest from Manila, had been dormant for 6 centuries before the 1991 eruption, which ranks as one of the largest eruptions in the 20th century. In 1991, Japan's Unzen Volcano, located on the island of Kyushu about 40 km east of Nagasaki, awakened from its 200-year slumber to produce a new lava dome at its summit. Beginning in June, repeated collapse of this erupting dome generated ash flows that swept down the mountain's slopes at speeds as high as 200 km/h. Unzen is one of more than 75 active volcanoes in Japan; the eruption of Mount Vesuvius in 79 smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and lava flows. Although death toll is estimated between 13,000 and 26,000 remains, the exact number still remains unknown. Vesuvius is recognized as one of the most dangerous volcanoes, due to its
Not to be confused with: Town of Mount Charleston, Nevada. Mount Charleston named Charleston Peak, at 11,916 feet, is the highest mountain in both the Spring Mountains and Clark County, in Nevada, United States, it is the eighth-highest mountain in the state. Well separated from higher peaks by large, low basins, it is the most topographically prominent peak in Nevada, the eighth-most-prominent peak in the contiguous United States, it is one of eight ultra-prominent peaks in Nevada. It is located about 35 miles northwest of Las Vegas within the Mount Charleston Wilderness, within the Spring Mountains National Recreation Area of the Humboldt-Toiyabe National Forest. Mount Charleston is a year-round getaway for Las Vegas's residents and visitors, with a number of hiking trails and a modest ski area; the mountain, snow-capped more than half the year, can be seen from parts of the Las Vegas Strip when looking toward the west. Mount Charleston has nearly 200 camp sites and over 150 picnic areas, some of which are RV-accessible.
The village of Mount Charleston lies at its base to the east. The state of Nevada issues license plates with the caption "Mt. Charleston" and an image of the peak in the background. Sales of the plate supports the natural environment of the Mount Charleston area through grants administered by the Nevada Division of State Lands. According to the Federal Writers' Project, Mount Charleston was named for Charleston, South Carolina by southern sympathizers. Near its summit are the remnants of a 1955 plane crash. A CIA C-54 Military Air Transport Service plane crashed near the peak on November 17, 1955 during a blizzard; the plane was on route from Groom Lake to nearby Area 51 to work on a secret U-2 plane development. Fourteen men were on board. There are still remains from the plane that can be hiked to just off the main southern loop trail to the peak. A memorial featuring the propeller from the downed aircraft was installed at the Spring Mountains Visitor Gateway in 2015, it was Nevada’s first national memorial and the first on U.
S. Forest Service land. Charleston Peak is a popular destination for hikers; the summit offers panoramic views from the Sierra Nevada, Death Valley, Las Vegas. There are two well-marked and well-maintened trails to the summit: South Loop Trail and North Loop/Trail Canyon; the trails can be combined as a loop. Both approaches involve a strenuous 16-mile+ round trip with over 4000 feet of climbing; the hike takes all day. The hike is most accessible in the snow-free months of fall. List of Ultras of the United States Carpenter 1 Fire "Charleston Peak". SummitPost.org
Mount Shishaldin is a moderately active volcano on Unimak Island in the Aleutian Islands chain of Alaska. It is the highest mountain peak of the Aleutian Islands; the most symmetrical cone-shaped glacier-clad large mountain on earth, the volcano's topographic contour lines are nearly perfect circles above 6,500 feet. The lower north and south slopes are somewhat steeper than western slopes; the volcano is the westernmost of three large stratovolcanoes along an east–west line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." The upper 6,600 ft is entirely covered by glacial snow and ice. In all, Shishaldin's glacial shield covers about 35 square miles, it is flanked to the northwest by 24 monogenetic parasitic cones, an area blanketed by massive lava flows. The Shishaldin cone is less than 10,000 years old and is constructed on a glacially eroded remnant of an ancestral somma and shield. Remnants of the older ancestral volcano are exposed on the west and northeast sides at 4,900 to 5,900 ft elevation.
The Shishaldin edifice contains about 120 square miles of material. A steady steam plume rises from its small summit crater, about 500 ft across and breached along the north rim. In 1967, Shishaldin Volcano was designated as a National Natural Landmark by the National Park Service; this volcano has had many recorded eruptions during the 19th and 20th centuries, a couple reports of volcanic activity in the area during the 18th century may have referred to Shishaldin as well. Therefore, the volcano's entire recorded history is spotted with reports of activity. AVO has 24 confirmed eruptions at Shishaldin, making it the volcano with the third most confirmed eruptions. However, Shishaldin has the most eruptions in Alaska, but half of the eruptions are unconfirmed, with the most recent one being in January 2015. Mount Shishaldin's most recent eruptions were in 1995–96 and 1999. Since the 1999 eruption, it has maintained seismic activity having low-magnitude volcanic earthquakes every 1–2 minutes. During this period of non-eruptive seismic activity, it has been puffing steam, with puffs occurring about every 1–2 minutes.
There were reports in 2004 of small quantities of ash being emitted with the steam. The Alaska Volcano Observatory monitors the volcano for more hazardous activity with seismometers and satellite images. Visual observations are rare, because of the remote location of the volcano; the first recorded ascent of Shishaldin was by G. Peterson and two companions. Given the straightforward nature of the climbing, it is possible that an earlier ascent occurred, either by native Aleuts, Russians, or other visitors. Shishaldin is a popular ski descent for local climbers. Due to its remoteness, Shishaldin is not climbed by outsiders. List of mountain peaks of North America List of mountain peaks of the United States List of mountain peaks of Alaska List of Ultras of the United States List of volcanoes in the United States "Shishaldin". Global Volcanism Program. Smithsonian Institution. Petersen, Tanja.
San Jacinto Peak
San Jacinto Peak is the highest peak of the San Jacinto Mountains, of Riverside County, California. It lies within Mount San Jacinto State Park. Naturalist John Muir wrote of San Jacinto Peak, "The view from San Jacinto is the most sublime spectacle to be found anywhere on this earth!"San Jacinto Peak is one of the most topographically prominent peaks in the United States. It is ranked sixth among peaks in the 48 contiguous states. According to John W. Robinson and Bruce D. Risher, authors of The San Jacintos, "No Southern California hiker worth his salt would miss climbing'San Jack' at least once."Known for its spectacular north escarpment, the peak rises 10,000 feet above San Gorgonio Pass. It plays host to the famous Cactus to Clouds Trail. To the east, the peak towers over the city of Palm Springs; the peak is frequently called Mount San Jacinto. The steep escarpment of its north face, above Snow Creek, climbs over 10,000 feet in 7 miles; this is one of the largest gains in elevation over such a small horizontal distance in the contiguous United States.
From the peak, San Gorgonio Mountain can be seen across the San Gorgonio Pass. Visible below is the Coachella Valley and the Salton Sea. In addition, much of the Inland Empire, including Ontario to the west, can be viewed on a clear day. Mount San Jacinto is one of the "Four Saints," a name used to describe the high points of the four mountains over 10,000 feet named for Catholic saints in Southern California: San Jacinto Peak, Mount San Gorgonio, San Bernardino Peak, Mount San Antonio. To the Cahuilla Indians, the peak was known as I a kitch, meaning "smooth cliffs." It was the home of the meteor and legendary founder of the Cahuilla. In 1878, a Wheeler Survey topographical party led by rancher Charles Thomas of Garner Valley climbed the peak; the Wheeler Survey gave the mountain the name "San Jacinto Peak" The earliest recorded ascent of the peak was made in September, 1874 by "F. of Riverside," according to a description of his ascent in the San Diego Union. The first successful ascent of the difficult northeast escarpment was made in 1931 by Floyd Vernoy and Stewart White of Riverside.
The peak is flanked by Marion Mountain. These peaks were named in 1897 by USGS topographer Edmund Taylor Perkins, Jr. Perkins named Jean Peak for his sweetheart and future bride, Jean Waters of Plumas County, whom he married in 1903, he named Marion Mountain after Marion Kelly, his girlfriend, a teacher for the Indian Bureau at the Morongo Valley Reservation. According to a local legend, Perkins spent the summer of 1897 deciding which woman to marry while he conducted his topographical survey of San Jacinto Peak and its environs. Nearby Cornell Peak is named for the alma mater of geologist Robert T. Hill. Perkins and Hill were camping in Round Valley when Hill remarked that the peak looked like the campanile tower at Cornell. Perkins named the peak Cornell Peak. In 1931 and 1932, the San Jacinto Mountain Chamber of Commerce sponsored a Labor Day footrace from Idyllwild to San Jacinto Peak and back, a distance of 18 miles and 5,300 feet; the 1931 race was won by Tom Humphreys, a Hopi, in 3:36:30.
Humphreys won the race again in 1932 with a time of 3:12. Near the summit of San Jacinto peak is a stone hut, built in 1935 by the Civilian Conservation Corps under the direction of Serbo-Croatian immigrant Alfred Zarubicka, a stonemason known in Idyllwild as "Zubi." San Jacinto Peak is accessible, as many trails penetrate the Santa Rosa and San Jacinto Mountains National Monument. The most popular route starts with a ride on the Palm Springs Aerial Tramway from Valley Station at 2,643 feet near Palm Springs up to Mountain Station at 8,516 feet. From there, one can climb the mountain face via trails. Another route is to hike the Marion Mountain Trail from near the mountain town of Idyllwild. There is a reproducing but introduced population of Sequoiadendrons planted in 1974 located here hundreds of miles from native populations; the Cactus to Clouds Trail involves an arduous climb of 10,700 feet from the desert floor in Palm Springs to the summit at 10,834 feet. This trail has no water sources until 8,500 feet, so early starts are advised to avoid the temperatures which soar above 100 °F.
List of highest points in California by county List of Ultras of the United States "Mount San Jacinto State Park". California State Parks. Retrieved 2009-08-17. Mount San Jacinto State Park map. Mount San Jacinto State Park. Retrieved 2015-11-24. "San Jacinto Peak". SummitPost.org. Retrieved 2011-05-07. "Cactus to Clouds Hiking Guide". Mt. San Jacinto Message Board. Archived from the original on 2009-10-25. Retrieved 2009-08-17. "Main page". Riverside Mountain Rescue Unit. Retrieved 2009-08-17. "Forum Index". Mt. San Jacinto Outdoor Recreation. Retrieved 2009-08-17. Howser, Huell. "Mt. San Jacinto – California's Gold". California's Gold. Chapman University Huell Howser Archive
Mauna Kea is a dormant volcano on the island of Hawaii. Its peak is 4,207.3 m above sea level. Most of the mountain is under water, when measured from its oceanic base, Mauna Kea is the tallest mountain in the world measuring over 10,000 m. Mauna Kea is about a million years old, has thus passed the most active shield stage of life hundreds of thousands of years ago. In its current post-shield state, its lava is more viscous. Late volcanism has given it a much rougher appearance than its neighboring volcanoes due to construction of cinder cones, decentralization of its rift zones, glaciation on its peak, weathering by the prevailing trade winds. Mauna Kea last is now considered dormant; the peak is about 38 m higher than its more massive neighbor. In Hawaiian mythology, the peaks of the island of Hawaii are sacred. An ancient law allowed only high-ranking aliʻi to visit its peak. Ancient Hawaiians living on the slopes of Mauna Kea relied on its extensive forests for food, quarried the dense volcano-glacial basalts on its flanks for tool production.
When Europeans arrived in the late 18th century, settlers introduced cattle and game animals, many of which became feral and began to damage the mountain's ecological balance. Mauna Kea can be ecologically divided into three sections: an alpine climate at its summit, a Sophora chrysophylla–Myoporum sandwicense forest on its flanks, an Acacia koa–Metrosideros polymorpha forest, now cleared by the former sugar industry, at its base. In recent years, concern over the vulnerability of the native species has led to court cases that have forced the Hawai'i Department of Land and Natural Resources to eradicate all feral species on the mountain. With its high elevation, dry environment, stable airflow, Mauna Kea's summit is one of the best sites in the world for astronomical observation. Since the creation of an access road in 1964, thirteen telescopes funded by eleven countries have been constructed at the summit; the Mauna Kea Observatories are used for scientific research across the electromagnetic spectrum and comprise the largest such facility in the world.
Their construction on a landscape considered sacred by Native Hawaiians continues to be a topic of debate. Mauna Kea is one of five volcanoes that form the island of Hawaii, the largest and youngest island of the Hawaiian–Emperor seamount chain. Of these five hotspot volcanoes, Mauna Kea is the fourth oldest and fourth most active, it began as a preshield volcano driven by the Hawaii hotspot around one million years ago, became exceptionally active during its shield stage until 500,000 years ago. Mauna Kea entered its quieter post-shield stage 250,000 to 200,000 years ago, is dormant. Mauna Kea does not have a visible summit caldera, but contains a number of small cinder and pumice cones near its summit. A former summit caldera may have been filled and buried by summit eruption deposits. Mauna Kea is over 32,000 km3 in volume, so massive that it and its neighbor, Mauna Loa, depress the ocean crust beneath it by 6 km; the volcano continues to slip and flatten under its own weight at a rate of less than 0.2 mm per year.
Much of its mass lies east of its present summit. Mauna Kea stands 4,207.3 m above sea level, about 38 m higher than its neighbor Mauna Loa, is the highest point in the state of Hawaii. Measured from its base on the ocean floor, it rises over 10,000 m greater than the elevation of Mount Everest above sea level. Like all Hawaiian volcanoes, Mauna Kea has been created as the Pacific tectonic plate has moved over the Hawaiian hotspot in the Earth's underlying mantle; the Hawaii island volcanoes are the most recent evidence of this process that, over 70 million years, has created the 6,000 km -long Hawaiian Ridge–Emperor seamount chain. The prevailing, though not settled, view is that the hotspot has been stationary within the planet's mantle for much, if not all of the Cenozoic Era. However, while Hawaiian volcanism is well understood and extensively studied, there remains no definite explanation of the mechanism that causes the hotspot effect. Lava flows from Mauna Kea overlapped in complex layers with those of its neighbors during its growth.
Most prominently, Mauna Kea is built upon older flows from Kohala to the northwest, intersects the base of Mauna Loa to the south. The original eruptive fissures in the flanks of Mauna Kea were buried by its post-shield volcanism. Hilo Ridge, a prominent underwater rift zone structure east of Mauna Kea, was once believed to be a part of the volcano; the shield-stage lavas that built the enormous main mass of the mountain are tholeiitic basalts, like those of Mauna Loa, created through the mixing of primary magma and subducted oceanic crust. They are covered by the oldest exposed rock strata on Mauna Kea, the post-shield alkali basalts of the Hāmākua Volcanics, which erupted between 250,000 and 70–65,000 years ago; the most recent volcanic flows are hawaiites and mugearites: they are the post-shield Laupāhoehoe Volcanics, erupted between 65,000 and 4,000 years ago. These changes in lava composition accompanied the slow reduction of the supply of magma to the summit, which led to weaker eruptions that gave way to isolated episodes associated with volcanic dormancy.
The Laupāhoehoe lavas are more viscous and contain more volatiles than the earlier tholeiitic basalts.
Types of volcanic eruptions
Several types of volcanic eruptions—during which lava and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are 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. There are three different types of eruptions; the most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity; the third eruptive type is the phreatic eruption, driven by the superheating of steam via contact with magma. Within these wide-defining eruptive types are several subtypes; the weakest are Hawaiian and submarine Strombolian, followed by Vulcanian and Surtseyan.
The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions. Subglacial and phreatic eruptions are defined by their eruptive mechanism, vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index, an order of magnitude scale ranging from 0 to 8 that correlates to eruptive types. Volcanic eruptions arise through three main mechanisms: Gas release under decompression causing magmatic eruptions Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions Ejection of entrained particles during steam eruptions causing phreatic eruptionsThere are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels tephra. Effusive eruptions, are characterized by the outpouring of lava without significant explosive eruption. Volcanic eruptions vary in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are not dangerous.
On the other extreme, Plinian eruptions are large and dangerous explosive events. Volcanoes are not bound to one eruptive style, display many different types, both passive and explosive in the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either; some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones, some of the strongest Surtseyan eruptions develop along fracture zones. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years, but Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was triggered by magma that took a nonstop route from the mantle over just a few months. The Volcanic Explosivity Index is a scale, for measuring the strength of eruptions, it is used by the Smithsonian Institution's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows.
It operates in a way similar to the Richter scale for earthquakes, in that each interval in value represents a tenfold increasing in magnitude. The vast majority of volcanic eruptions are of VEIs between 0 and 2. Volcanic eruptions by VEI index Magmatic eruptions produce juvenile clasts during explosive decompression from gas release, they range in intensity from the small lava fountains on Hawaii to catastrophic Ultra-Plinian eruption columns more than 30 km high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii. Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of fluid basalt-type lavas with low gaseous content; the volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the broad form of a shield volcano.
Eruptions are not centralized at the main summit as with other volcanic types, occur at vents around the summit and from fissure vents radiating out of the center. Hawaiian eruptions begin as a line of vent eruptions along a fissure vent, a so-called "curtain of fire." These die down. Central-vent eruptions, meanwhile take the form of large lava fountains, which can reach heights of hundreds of meters or more; the particles from lava fountains cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments. If eruptive rates are high enough, they may form splatter-fed lava flows. Hawaiian eruptions are extremely long lived. Another Hawaiian volcanic feature is the formation of active lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock. Flows from Hawaiian eruptions are basal