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103-496: The area was named after the dominating geological feature Kohala Mountain , the oldest of Hawaiʻi Island's five major volcanic mountains. The current districts cover the north and western sides of the mountain, 20°7′55″N 155°47′38″W  /  20.13194°N 155.79389°W  / 20.13194; -155.79389 . It was one of the five ancient divisions of the island called moku . The natural habitats in Kohala range across

206-778: A correlation with age of the forming lava, with in the case of the Hawaiian chain, steepness increasing with age, as later lavas tend to be more alkali so are more viscous, with thicker flows, that travel less distance from the summit vents. In height they are typically about one twentieth their width. Although the general form of a "typical" shield volcano varies little worldwide, there are regional differences in their size and morphological characteristics. Typical shield volcanoes found in California and Oregon measure 3 to 4 mi (5 to 6 km) in diameter and 1,500 to 2,000 ft (500 to 600 m) in height, while shield volcanoes in

309-413: A landslide destroyed the northeast flank of the volcano, reducing its height by over 1,000 m (3,300 ft) and traveling 130 km (81 mi) across the sea floor . This huge landslide may be partially responsible for the volcano's foot-like shape. Marine fossils have been found on the flank of the volcano, far too high to have been deposited by standard ocean waves . Analysis indicated that

412-545: A far greater distance than those of other eruptive types before solidifying, forming extremely wide but relatively thin magmatic sheets often less than 1 m (3 ft) thick. Low volumes of such lavas layered over long periods of time are what slowly constructs the characteristically low, broad profile of a mature shield volcano. Also unlike other eruptive types, Hawaiian eruptions often occur at decentralized fissure vents , beginning with large "curtains of fire" that quickly die down and concentrate at specific locations on

515-442: A flat crater floor surrounded by cones and fault scarps, the main caldera is affected relatively little by erosion from water. Most of Kohala's summit groundwater ends up in either Waipi'o or Honokane Nui; the enormous amount of water routed through these valleys results in a large amount of water erosion , which causes the valley walls to frequently collapse, accelerating valley development. This abundance of surface water inspired

618-457: A further 13 km (8 mi) below the waterline and into the crust, approximately 80,000 km (19,000 cu mi) of rock. Kīlauea , another Hawaiian shield volcano, is one of the most active volcanoes on Earth, with its most recent eruption occurring in 2021. The Galápagos Islands are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, about 1,100 km (680 mi) west of Ecuador. They are driven by

721-399: A primary factor in the development of the largest valleys, the dike complex plays another important role —that of creating and maintaining the water table . Hawaiian lava is extremely permeable and porous . Rainwater easily seeps into the lava, creating a large lens of fresh water below the island surface. In most places, the top of the water table is just a few feet from sea level, as

824-583: A prominent feature on these volcanoes and account for their seemingly random volcanic structure. They are fueled by the movement of the Pacific Plate over the Hawaii hotspot and form a long chain of volcanoes, atolls , and seamounts 2,600 km (1,616 mi) long with a total volume of over 750,000 km (179,935 cu mi). The chain includes Mauna Loa, a shield volcano which stands 4,170 m (13,680 ft) above sea level and reaches

927-425: A series of stone paths that divided the farmed area into plots of variable size. These structures are unique because although many people used such systems at the time, Kohala has some of the few to survive. The leeward slopes of Kohala were used for sugarcane plantations in the late 19th century. The trip from the fields to the mills and then boats was mechanized by steam locomotive in 1883. Several plantations on

1030-440: A single point. The main shield then forms, burying the smaller ones formed by the early eruptions with its lava. Icelandic shields are mostly small (~15 km (4 cu mi)), symmetrical (although this can be affected by surface topography), and characterized by eruptions from summit calderas. They are composed of either tholeiitic olivine or picritic basalt . The tholeiitic shields tend to be wider and shallower than

1133-415: A thick layer of ferns and mosses carpeting the floor, which act as sponges, absorbing water from rain and passing much of it through to the groundwater in aquifers below; when feral animals like pigs trample the covering, the forest loses its ability to hold in water effectively, and instead of recharging the aquifer, it results in a severe loss of topsoil , much of which ends up being dumped by streams into

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1236-406: A very high ratio of the species present being found nowhere else on Earth. Only about 2.5% of the world's rainforest is cloud rainforest, making it a unique habitat as well. The mountain supports approximately 155 native species of vertebrates , crustaceans , mollusks , and plants . A diverse complexion of fungi , liverwort , and mosses further add to the variety. In fact, up to a quarter of

1339-469: A wide rainfall gradient in a very short distance - from less than 5 inches (130 mm) a year on the coast near Kawaihae to more than 150 inches (3,800 mm) year near the summit of Kohala Mountain, a distance of just 11 miles (18 km). Near the coast are remnants of dry forests , and near the summit is a cloud forest , a type of rainforest that obtains some of its moisture from "cloud drip" in addition to precipitation. This precipitation allowed

1442-461: Is Nyamuragira . Eruptions at the shield volcano are generally centered within the large summit caldera or on the numerous fissures and cinder cones on the volcano's flanks. Lava flows from the most recent century extend down the flanks more than 30 km (19 mi) from the summit, reaching as far as Lake Kivu . Erta Ale in Ethiopia is another active shield volcano and one of the few places in

1545-642: Is "to respectfully engage the Island of Hawaiʻi as an extraordinary and vibrant research and learning laboratory for humanity." The land around Kohala is administered as two districts, North Kohala and South Kohala, of the County of Hawaiʻi . The beaches, parks, golf courses, and resorts in South Kohala are called "the Kohala Coast." King Kamehameha I , the first King of the unified Hawaiian Islands ,

1648-454: Is 606 km (234 sq mi) in area and 14,000 km (3,400 cu mi) in volume , and thus constitutes just under 6% of the island of Hawaii. Kohala is a shield volcano cut by multiple deep gorges , which are the product of thousands of years of erosion . Unlike the typical symmetry of other Hawaiian volcanoes, Kohala is shaped like a foot. Toward the end of its shield-building stage 250,000 to 300,000 years ago,

1751-667: Is a shield volcano on the southwestern part of Isabela Island and is one of the most active in the Galapagos, with the last eruption between May and June 2008. The Geophysics Institute at the National Polytechnic School in Quito houses an international team of seismologists and volcanologists whose responsibility is to monitor Ecuador's numerous active volcanoes in the Andean Volcanic Belt and

1854-400: Is a small string of faults on and near the main summit caldera , arranged parallel to the northern coast. The faults were originally regarded to be a direct result of the collapse; however scientists note the fault lines do not go all the way to the coast but are arranged tightly clustered around the caldera. This indicates that the fault lines may have been caused indirectly, possibly due to

1957-468: Is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity ) lava , which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano . Repeated eruptions result in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form. Shield volcanoes are found wherever fluid, low- silica lava reaches

2060-549: Is believed that bogs form in low-lying areas where clay in the soil prevents proper water drainage, resulting in an accumulation of water that impedes the root systems of woody plants . Kohala's bogs are characterized by sedges , mosses of the genus Sphagnum , and oha wai, native members of the bellflower family. Other habitats include rain forest and mesophytic (wet) forests. The same isolation that produced Kohala's unique ecosystem also makes it very vulnerable to invasive species . Alien plants and feral animals are among

2163-531: Is common in Hawaiʻi; most Hawaiian eruptions begin with a so-called "wall of fire" along a major fissure line before centralizing to a small number of points. This accounts for their asymmetrical shape, whereas Icelandic volcanoes follow a pattern of central eruptions dominated by summit calderas , causing the lava to be more evenly distributed or symmetrical. Most of what is currently known about shield volcanic eruptive character has been gleaned from studies done on

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2266-471: Is mostly 260,000 to 140,000 years old, and composed mainly of hawaiite and trachyte . The separation between the two layers is not clear; the lowest layers may actually be in the Pololu section, based on their depositional patterns and low phosphorus content. The time intervals separating the two periods of volcanic evolution were extremely brief, something first noted in 1988. The forest-covered summit of

2369-399: Is relatively smooth and flows with a ropey texture, and ʻaʻā flows which are denser, more viscous (and thus slower moving) and blockier. These lava flows can be anywhere between 2 and 20 m (10 and 70 ft) thick. ʻAʻā lava flows move through pressure— the partially solidified front of the flow steepens because of the mass of flowing lava behind it until it breaks off, after which

2472-441: Is served commercially by Mokulele Airlines. Kohala (mountain) Kohala is the oldest of five volcanoes that make up the island of Hawaii . Kohala is an estimated one million years old—so old that it experienced, and recorded, the reversal of Earth's magnetic field 780,000 years ago. It is believed to have breached sea level more than 500,000 years ago and to have last erupted 120,000 years ago. Kohala

2575-534: Is taken from the German term Schildvulkan , coined by the Austrian geologist Eduard Suess in 1888 and which had been calqued into English by 1910. Shield volcanoes are distinguished from the three other major volcanic types— stratovolcanoes , lava domes , and cinder cones —by their structural form, a consequence of their particular magmatic composition. Of these four forms, shield volcanoes erupt

2678-479: The Galápagos hotspot , and are between approximately 4.2 million and 700,000 years of age. The largest island, Isabela , consists of six coalesced shield volcanoes, each delineated by a large summit caldera. Española , the oldest island, and Fernandina , the youngest, are also shield volcanoes, as are most of the other islands in the chain. The Galápagos Islands are perched on a large lava plateau known as

2781-685: The Mid-Atlantic Ridge , a divergent tectonic plate boundary in the middle of the Atlantic Ocean, Iceland is the site of about 130 volcanoes of various types. Icelandic shield volcanoes are generally of Holocene age, between 5,000 and 10,000 years old. The volcanoes are also very narrow in distribution, occurring in two bands in the West and North Volcanic Zones. Like Hawaiian volcanoes, their formation initially begins with several eruptive centers before centralizing and concentrating at

2884-734: The Moʻokini Heiau . The heiau is a living spiritual temple, and not just an historic artifact of the Hawaiian culture. The original Kamehameha Statue stands in front of the community center in Kapaʻau, and duplicates are found at Aliʻiolani Hale in Honolulu , and within the U.S. Capitol building's statue gallery in Washington, D.C. The Bond Historic District is located in the North Kohala District, with structures from

2987-512: The 16 smaller streams between Waikoloa Stream and the Wailoa river in Waipi'o Valley. The natural habitats in the Kohala district range across a wide rainfall gradient in a very short distance—from less than 5 in (130 mm) a year on the coast near Kawaihae, to more than 150 in (3,800 mm) a year near the summit of Kohala Mountain, a distance of just 11 mi (18 km). At

3090-421: The 1976–1979 Viking mission . The principal difference between the volcanoes of Mars and those on Earth is in terms of size; Martian volcanoes range in size up to 14 mi (23 km) high and 370 mi (595 km) in diameter, far larger than the 6 mi (10 km) high, 74 mi (119 km) wide Hawaiian shields. The highest of these, Olympus Mons , is the tallest known mountain on any planet in

3193-515: The Bond family's 19th century missionary and homesteading period on the Kohala peninsula. The Bond District has three sections: Points of interest within Kohala include Hapuna Beach State Recreation Area , Puʻukoholā Heiau National Historic Site , and Lapakahi State Historical Park . Major thoroughfares within Kohala include Akoni Pule Highway (Hawaii state route 270) which provides access to Pololū Valley . The Hawaii Belt Road which connects in

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3296-568: The Galapagos Islands. La Cumbre is an active shield volcano on Fernandina Island that has been erupting since April 11, 2009. The Galápagos islands are geologically young for such a big chain, and the pattern of their rift zones follows one of two trends, one north-northwest, and one east–west. The composition of the lavas of the Galápagos shields are strikingly similar to those of the Hawaiian volcanoes. Curiously, they do not form

3399-535: The Galápagos Platform. This platform creates a shallow water depth of 360 to 900 m (1,181 to 2,953 ft) at the base of the islands, which stretch over a 174 mi (280 km) diameter. Since Charles Darwin 's visit to the islands in 1835 during the second voyage of HMS Beagle , there have been over 60 recorded eruptions in the islands, from six different shield volcanoes. Of the 21 emergent volcanoes, 13 are considered active. Cerro Azul

3502-456: The Kohala watershed and to protect it from threats, most especially invasive species. Another project to raise awareness of Kohala's ecosystem is The Kohala Center , an independent, not-for-profit , community-based organization for research and education. It was established as a response to requests by island residents to create an educational and employment opportunity related to Hawaii's natural and cultural significance. The center's mission

3605-661: The Leeward side of the volcano for centuries. The northern part of the island is named after the mountain, with two districts named North and South Kohala. King Kamehameha I , the first King of the Kingdom of Hawaii , was born in North Kohala , near Hawi . Studies of the volcano's lava accumulation rate have put the volcano's age at somewhere near one million years. It is believed to have breached sea level more than 500,000 years ago. Beginning 300,000 years ago,

3708-782: The accumulation of fragmentary material from particularly powerful explosive eruptions, and rarer felsic lava shields formed by unusually fluid felsic magmas. Examples of pyroclastic shields include Billy Mitchell volcano in Papua New Guinea and the Purico complex in Chile ; an example of a felsic shield is the Ilgachuz Range in British Columbia , Canada. Shield volcanoes are similar in origin to vast lava plateaus and flood basalts present in various parts of

3811-770: The actual valley walls at the seashore range from 300 m (1,000 ft) at the Waipiʻo Valley Lookout at the southeastern corner of Kohala mountain, to a high of over 500 m (1,600 ft) in Honopue, then diminishing to less than 150 m (490 ft) at Pololu Lookout at the northern end of the valleys. In the back, deeper in the mountain, all of the valleys have sheer walls well in excess of 1,000 m (3,300 ft). Numerous spectacular waterfalls cascade or fall over these cliffs. Some, such as Hi'ilawe Falls in Waipi'o valley, have single drops exceeding 300 m (1,000 ft). The volcano stayed active well into

3914-494: The base of the volcano 6 km (3.7 mi) inshore. A research team led by University of Hawaii's Gary McMurtry and Dave Tappin of the British Geological Survey found that the fossils had been deposited by a massive tsunami , 61 m (200 ft) above the current sea level. The team dated the fossils and nearby volcanic rock at about 120,000 years old. Based on the rate of Kohala's subsidence over

4017-508: The central Mexican Michoacán–Guanajuato volcanic field average 340 m (1,100 ft) in height and 4,100 m (13,500 ft) in width, with an average slope angle of 9.4° and an average volume of 1.7 km (0.4 cu mi). Rift zones are a prevalent feature on shield volcanoes that is rare on other volcanic types. The large, decentralized shape of Hawaiian volcanoes as compared to their smaller, symmetrical Icelandic cousins can be attributed to rift eruptions. Fissure venting

4120-514: The coast are remnants of dry forests , and near the summit lies a cloud forest , a type of rainforest that obtains much of its moisture from "cloud drip" in addition to precipitation . These large cloud forests dominate its slopes. This biome is rare, and contains a disproportionate percentage of the world's rare and endemic species. The soil at Kohala is nitrogen-rich , facilitating root growth . The happy combination of small trees, bushes, ferns, vines, and other forms of ground cover keep

4223-451: The extents of the volcano have not been confirmed. Although Tamu Massif was initially believed to be a shield volcano, Sanger and his colleagues acknowledged in 2019 that Tamu Massif is not a shield volcano. Shield volcanoes feature a gentle (usually 2° to 3°) slope that gradually steepens with elevation (reaching approximately 10°) before flattening near the summit, forming an overall upwardly convex shape. These slope characteristics have

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4326-630: The first of Kohala's three massive irrigation diversion "ditches", the Upper Hamakua Ditch, although the water was initially used for transporting ("fluming") sugarcane to the mills rather than irrigation. Surface water supplies, however, were not stable enough for the large scale plantation economy developing in Hamakua and North Kohala, so later ditches tapped the spring fed base flows of the valleys and larger gulches. Only Waimanu Valley escaped with none of its tributaries tapped, along with

4429-401: The flanks of the volcano. North of Kohala's summit the volcano's northwest–southeast trending rift zone separates rainfall into two streams, going southeast, into Waipiʻo Valley, or northwest, into Honokane Nui Valley. When the volcano was still active, vertical sheets of magma, arranged in what is known as dikes , forced their way out of the magma reservoir and intruded into the rift zone, which

4532-416: The formation of these mountainside valleys, as illustrated by later Pololu lava flows, which covered the north and northwestern end of Kohala volcano and often flowed into Pololu Valley . Recent seafloor mapping seems to show that the valley extends a short way beyond the seashore, then terminates at what may be the headwall of the great landslide found off the northeast coast of Kohala. In addition to being

4635-404: The fossils had been deposited by a massive tsunami approximately 120,000 years ago. Because it is so far from the nearest major landmass, the ecosystem of Kohala has experienced geographic isolation , resulting in a unique ecosystem. There are several initiatives to preserve this ecosystem against invasive species. Crops, especially sweet potato (Ipomoea batatas) , have been cultivated on

4738-399: The fresh water lens is floating on salt water. Unlike porous lava flows, however, dikes cool underground into dense rock with few cracks and vesicles . The dikes act as impermeable vertical walls through which groundwater cannot flow. Deep layers of ash compact into impermeable layers between lava flows, preventing percolation of the rainwater. Rainwater that would ordinarily seep right through

4841-410: The general mass behind it moves forward. Though the top of the flow quickly cools down, the molten underbelly of the flow is buffered by the solidifying rock above it, and by this mechanism, ʻaʻā flows can sustain movement for long periods of time. Pāhoehoe flows, in contrast, move in more conventional sheets, or by the advancement of lava "toes" in snaking lava columns. Increasing viscosity on the part of

4944-472: The greatest threats to the local ecology. Plants like the kahili ginger (Hedychium gardnerianum) and the strawberry guava (Psidium cattleinum) displace native species. Prior to human settlement, many major organisms such as conifers and rodents never made it onto the island, so the ecosystem never developed defenses against them, leaving Hawaii vulnerable to damage by hoofed animals , rodents, and predation . Kohala's native Hawaiian rain forest has

5047-419: The ground gets trapped in the dike "reservoirs," located well above sea level. The groundwater is confined to a flow along the dike until it finds a means to escape. In Kohala, the numerous dikes near the summit inhibit groundwater from seeping downslope to the northeast, where it naturally wants to go. Rather, the Kohala dike complex guides it northwest or southeast, down the axis of the rift zones, just like

5150-573: The height of the volcano above the sea floor , the "true" height of Mauna Loa from the start of its eruptive history is about 17,170 m (56,000 ft). Mount Everest , by comparison, is 8,848 m (29,029 ft) in height. In 2013, a team led by the University of Houston 's William Sager announced the discovery of Tamu Massif , an enormous extinct submarine volcano, approximately 450 by 650 km (280 by 400 mi) in area, which dwarfs all previously known volcanoes on Earth. However,

5253-504: The higher elevations and distribute it to the then-extensive sugarcane industry. In 1905, after 18 months and the loss of 17 lives, the Kohala Ditch, a vast network of flumes and ditches, measuring 22 mi (35 km) in length, was completed. It has since come into use by ranches, farms, and homes. A portion of the ditch became a tourist attraction until it was damaged by the 2006 Kiholo Bay earthquake , centered just southwest of

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5356-468: The largest volcanic features on Earth. The summit of the largest subaerial volcano in the world, Mauna Loa , lies 4,169 m (13,678 ft) above sea level , and the volcano, over 60 mi (100 km) wide at its base, is estimated to contain about 80,000 km (19,000 cu mi) of basalt. The mass of the volcano is so great that it has slumped the crust beneath it a further 8 km (5 mi). Accounting for this subsidence and for

5459-435: The last 780,000 years. Radiometric dating ranged mostly from 450,000 to 320,000 years ago, although several pieces strayed lower; this indicated a period of eruptive history at the time. Kohala was devastated by a massive landslide between 250,000 and 300,000 years before present . Debris from the slide was found on the ocean floor up to 130 km (81 mi) away from the volcano. Twenty kilometers wide at

5562-401: The lava flows that formed it; however, the northwest shoreline boasts some of the highest seacliffs on Earth. Events during and after its eruptions give the volcano several unique geomorphic features, some possibly resulting from the ancient collapse and landslide. The volcano is shaped like a foot; the northeast coast is prominently indented across 20 km (12 mi) of shoreline. There

5665-641: The lava or shear stress on the part of local topography can morph a pāhoehoe flow into an ʻaʻā one, but the reverse never occurs. Although most shield volcanoes are by volume almost entirely Hawaiian and basaltic in origin, they are rarely exclusively so. Some volcanoes, such as Mount Wrangell in Alaska and Cofre de Perote in Mexico, exhibit large enough swings in their historical magmatic eruptive characteristics to cast strict categorical assignment in doubt; one geological study of de Perote went so far as to suggest

5768-543: The least viscous lavas. Whereas stratovolcanoes and lava domes are the product of highly viscous flows, and cinder cones are constructed of explosively eruptive tephra , shield volcanoes are the product of gentle effusive eruptions of highly fluid lavas that produce, over time, a broad, gently sloped eponymous "shield". Although the term is generally applied to basaltic shields, it has also at times been applied to rarer scutiform volcanoes of differing magmatic composition—principally pyroclastic shields , formed by

5871-411: The life cycle of Hawaiian volcanoes. The United States Geological Survey has assessed the extinct Kohala as a low-risk area. The volcano is in zone 9 (bottom risk), while the border of the volcano with Mauna Kea is zone 8 (second lowest), as Mauna Kea has not produced lava flows for 4,500 years. Kohala, like other shield volcanoes, has a shallow surface slope due to the low viscosity of

5974-719: The most prominent ones are situated along the Snake River in Idaho and the Columbia River in Washington and Oregon, where they have been measured to be over 1 mi (2 km) in thickness. Calderas are a common feature on shield volcanoes. They are formed and reformed over the volcano's lifespan. Long eruptive periods form cinder cones, which then collapse over time to form calderas. The calderas are often filled up by progressive eruptions, or formed elsewhere, and this cycle of collapse and regeneration takes place throughout

6077-543: The mountain slope. Instead, the rainwater flows down laterally and empties into the back of what have thus become the largest valleys (Waipiʻo and Honokane Nui). The leeward northwestern slope of Kohala has few stream valleys cut into it, the result of the rain shadow effect, as the dominant trade winds bring most of the rainfall to the northeastern slope of the volcano. The seven windward valleys of Kohala are, from southeast to northwest, Waipiʻo, Waimanu, Honopue, Honokea, Honokane Iki, Honokane Nui, and Pololu. The size of

6180-553: The mountain were consolidated into the Kohala Sugar Company by 1937. At the peak of its production, the company had 600 employees, 13,000 acres (20 sq mi) of land, and a capacity of 45,000 t (99,000,000 lb) of raw sugar per year. In 1975 the company finally closed down. Kohala supports a very complex hydrological cycle . In the early part of the 20th century, this was exploited by building surface irrigational channels designed to capture water at

6283-504: The mountain. The Hawaii County Department of Water Supply relies on streams from Kohala to supply water to the population of the island. With increasing demand, the original surface channels have been supplemented by deep wells designed to channel groundwater for domestic use. In 2003 the Kohala Watershed Partnership was formed, a voluntary group of private land owners and state managers, designed to help manage

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6386-513: The nearby Mauna Kea and reappears further southeast in the Hilo Ridge , as indicated by the relationship between collected lava samples. In addition, the two features align to one another more closely than does the ridge to Mauna Kea, of which it was once thought to constitute a part. The bulk of the ridge is built of volcanic rock with reverse magnetic polarity, evidence that the volcano is at least 780,000 years old. Older lava dated from

6489-461: The northeast coast to be developed into sugarcane plantations , including one founded by Rev. Elias Bond used to fund his church and girls' seminary. The Kohala Historical Sites State Monument includes Moʻokini Heiau , a National Historic Landmark . King Kamehameha I , the first King of the unified Hawaiʻian Islands, was born in North Kohala west of Hāwī , at the ancient site called

6592-421: The ocean. There is evidence of pre-modern agriculture on the leeward slopes of Kohala. From 1400 to 1800, the principal crop grown at Kohala was sweet potato (Ipomoea batatas) , although there is also evidence of yams (Dioscorea sp.) , taro (Colocasia esculenta) , bananas (Musa hybrids) , sugarcane (Saccharum officinarum) , and gourds of the family Cucurbitaceae . The optimal rainfall level for

6695-433: The original size and shape of the volcano, as the southeast flank has been buried by volcanic lava flows from nearby Mauna Kea and Mauna Loa . However, based on a sharp increase of incline on the submarine slope of the volcano at a depth of 1,000 m (3,300 ft), scientists estimate that in its prime the portion of Kohala that was above the water was more than 50 km (31 mi) wide. Geologists estimate that

6798-462: The past 475,000 years, it was estimated that the fossils were deposited at a height of about 500 m (1,600 ft), well out of reach of storms and far above the normal sea level at the time. The timing corresponds with the last great landslide of nearby Mauna Loa . Researchers hypothesize that the underwater landslide from the nearby volcano triggered a gigantic tsunami, which swept up coral and other small marine organisms, depositing them on

6901-549: The picritic shields. They do not follow the pattern of caldera growth and destruction that other shield volcanoes do; caldera may form, but they generally do not disappear. Bingöl Mountains are one of the shield volcanoes in Turkey . In East Africa, volcanic activity is generated by the development of the East African Rift and from nearby hotspots. Some volcanoes interact with both. Shield volcanoes are found near

7004-402: The plants in the forest are mosses and ferns . These work to capture the water from clouds, in turn providing microhabitats for invertebrates and amphibians , and their predators. Estimates on the water capacity of the forest range from 320 to 1,600 US gal/acre (3,000 to 15,000 L/ha). The mountain is also home to several bogs , which exist as breaks in the cloud forests. It

7107-423: The rate of eruption slowly decreased over a long period of time to a point where erosion wore the volcano down faster than Kohala rebuilt itself through volcanic activity. Decreasing eruptions combined with increasing erosion caused Kohala to slowly weather away and subside into the ocean. The oldest lava flows that are still exposed at the surface are just under 780,000 years old. It is difficult to determine

7210-506: The rift and off the coast of Africa, although stratovolcanoes are more common. Although sparsely studied, the fact that all of its volcanoes are of Holocene age reflects how young the volcanic center is. One interesting characteristic of East African volcanism is a penchant for the formation of lava lakes ; these semi-permanent lava bodies, extremely rare elsewhere, form in about 9% of African eruptions. The most active shield volcano in Africa

7313-570: The same volcanic "line" associated with most hotspots. They are not alone in this regard; the Cobb–Eickelberg Seamount chain in the North Pacific is another example of such a delineated chain. In addition, there is no clear pattern of age between the volcanoes, suggesting a complicated, irregular pattern of creation. How the islands were formed remains a geological mystery, although several theories have been proposed. Located over

7416-434: The sea rapidly in the form of destructive floods, is fed gradually to the springs and to the underground artesian basins where it is held for use over a much longer interval... C S Judd, Superintendent of Forestry in Hawaiʻi, 1924 The forest lies perpendicular to the prevailing trade winds, a characteristic that leads to frequent cloud formation and abundant rainfall. Thus the rain forests carpeting Kohala are vital to

7519-424: The seafloor. The Hawaiian and Galápagos shields, and other hotspot shields like them, are constructed of oceanic island basalt. Their lavas are characterized by high levels of sodium , potassium , and aluminium . Features common in shield volcanism include lava tubes . Lava tubes are cave-like volcanic straights formed by the hardening of overlaying lava. These structures help further the propagation of lava, as

7622-420: The shoreline, the landslide cut back to the summit of the volcano, and is partially, if not largely, responsible for the volcano losing 1,000 m (3,300 ft) in height since then. The famous sea cliffs of the windward Kohala shoreline stand as evidence of the massive geologic disaster, and mark the topmost part of the debris from this ancient landslide. There are also several other unique features found on

7725-402: The site of one of the longest-lasting rift eruptions in known history. The Hawaiian shield volcanoes are not located near any plate boundaries ; the volcanic activity of this island chain is distributed by the movement of the oceanic plate over an upwelling of magma known as a hotspot . Over millions of years, the tectonic movement that moves continents also creates long volcanic trails across

7828-427: The soil porous and allow the water to percolate more easily into underground channels. The foliage of the trees breaks the force of rain and prevents the impact of soil by raindrops. A considerable portion of the precipitation is let down to the ground slowly by this three-story cover of trees, bushes, and floor plants and in this manner the rain, falling on a well-forested area, is held back and instead of rushing down to

7931-588: The southern end of the Akoni Pule Highway to Kona in the south and Hāmākua to the east. The Kohala Mountain Road (250) provides a link between Waimea and the Kohala CDP's of Halaʻula, Hāwī, and Kapaʻau. Kohala has two small airports. Upolu Airport is on Upolu Point at the northern tip of the island. Waimea-Kohala Airport is south of the town of Waimea, Hawaii County, Hawaii . Waimea Airport

8034-400: The sudden release of stress during the event. Mauna Kea causes the trade winds to divert around it, increasing wind to super-enhanced flow over the Kohala ridge and orographic lift brings most of the rainfall to the northeastern slope of Kohala. The windward side of Kohala mountain is dissected by multiple, deeply eroded stream valleys in a southwest–northeast alignment, cutting into

8137-499: The supply of groundwater on the island. The role of Kohala's ecosystem in supporting water flow has long been recognized. As early as 1902, US Forester E. M. Griffith wrote "Forest protection means not only increasing the rainfall, but more important still, conserving the water supply. The future welfare and agricultural prosperity of the Hawaiian Islands depends upon the preservation of the forest." Before humans arrived,

8240-463: The surface of a rocky planet. However, they are most characteristic of ocean island volcanism associated with hot spots or with continental rift volcanism. They include the largest active volcanoes on Earth, such as Mauna Loa . Giant shield volcanoes are found on other planets of the Solar System , including Olympus Mons on Mars and Sapas Mons on Venus . The term 'shield volcano'

8343-414: The surface water. On the other hand, the three smaller valleys between the large ones - Honopue, Honokea, and Honokane Iki - as well as the many smaller gulches which are not yet valleys, are deprived of groundwater by the orientation of the rift zone and its dikes. Without the large amount of water that is received by the bigger valleys, these valleys grow far more slowly. Due to its topography as essentially

8446-1082: The surface wells up), such as the Hawaiian–Emperor seamount chain and the Galápagos Islands , or over more conventional rift zones, such as the Icelandic shields and the shield volcanoes of East Africa. Although shield volcanoes are not usually associated with subduction , they can occur over subduction zones. Many examples are found in California and Oregon, including Prospect Peak in Lassen Volcanic National Park , as well as Pelican Butte and Belknap Crater in Oregon. Many shield volcanoes are found in ocean basins , such as Kīlauea in Hawaii, although they can be found inland as well—East Africa being one example of this. The largest and most prominent shield volcano chain in

8549-440: The surrounding heat, and hit the ground still hot, accumulating into spatter cones . If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long-lived; Puʻu ʻŌʻō , a cinder cone of Kīlauea , erupted continuously from January 3, 1983, until April 2018. Flows from Hawaiian eruptions can be divided into two types by their structural characteristics: pāhoehoe lava which

8652-496: The sweet potato lies between 30 and 50 inches (76–127 cm) per year. A combination of factors makes the rainfall at Kohala variable both from location to location and from year to year. In addition, Kohala is buffeted by strong winds, which are directly correlated to soil erosion; ancient farmers utilized a series of earthen embarkments and stone walls to protect their crops. This technique has been shown to reduce wind by at least 20–30 percent. In addition to walls, there are

8755-420: The term "compound shield-like volcano" instead. Most mature shield volcanoes have multiple cinder cones on their flanks, the results of tephra ejections common during incessant activity and markers of currently and formerly active sites on the volcano. An example of these parasitic cones is at Puʻu ʻŌʻō on Kīlauea —continuous activity ongoing since 1983 has built up a 2,290 ft (698 m) tall cone at

8858-549: The third largest valley, has its drainage almost exclusively from the north side of the summit, and as a result is a deep, long, narrow bottomed valley with little habitable floodplain. The remaining valleys derive all their water from the lower northeastern slopes of the volcano, and as a result are smaller. In addition, there are innumerable gulches of various depths which have not yet reached sea level and began to form flood plains, becoming valleys. Still, some of these are more than 300 m (1,000 ft) in depth. The depth of

8961-415: The toe of the ridge was estimated to be roughly between 1.1 and 1.2 million years old. Geologists have classified the volcano's lava flows into two units. The Hawi Volcanic layers were deposited in the postshield stage of the volcano's life, and the younger Pololu Volcanics were deposited in the volcano's shield-building stage. The rock in the younger Hawi section, which overlies the older Pololu flows,

9064-428: The valleys reflects the amount of drainage they have been able to capture; Waipiʻo, the largest, at some point drained Waimanu Valley as well, and the former headwaters of Waimanu are now one of its branches. Waimanu valley, cut off from its headwaters to the summit and left with Wai'ilikahi as its main tributary, still had managed to form a substantial floodplain, although less than half the size of Waipiʻo. Honokane Nui,

9167-460: The volcano consists of many cones which generated lava from its two rift zones between 240,000 and 120,000 years ago. Kohala completed its shield-building stage 245,000 years ago and has been in decline ever since. Potassium-argon dating indicates that the volcano last erupted about 120,000 years ago in the late Pleistocene . Kohala is currently in transition between the postshield and erosional Hawaiian volcanic stages in

9270-516: The volcano was once about twice its current size. The volcano is so old that it experienced, and recorded, a reversal of magnetic polarity (a change in the orientation of Earth's magnetic field so that the positions of the North and South poles interchange) that happened 780,000 years ago. Fifty flow units in the top 140 m (460 ft) of exposed strata in the Pololu section are of normal polarity, indicating that they were deposited within

9373-472: The volcano's lifespan. Interactions between water and lava at shield volcanoes can cause some eruptions to become hydrovolcanic . These explosive eruptions are drastically different from the usual shield volcanic activity and are especially prevalent at the waterbound volcanoes of the Hawaiian Isles . Shield volcanoes are found worldwide. They can form over hotspots (points where magma from below

9476-442: The volcano's rift zones. Central-vent eruptions, meanwhile, often take the form of large lava fountains (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments; however, when the air is especially thick with pyroclasts , they cannot cool off fast enough because of

9579-423: The volcano, all marks made by the decimating collapse. Kohala is thought to have last erupted 120,000 years ago. However, several samples of a more recent date have been obtained. Two samples collected about 120 m (390 ft) apart, obtained from Waipiʻo Valley on the volcano's east flank in 1977, were dated reliably to 60,000 years. Another double set of samples, collected from the western part in 1996,

9682-433: The volcanoes of Hawaiʻi Island , by far the most intensively studied of all shields because of their scientific accessibility; the island lends its name to the slow-moving, effusive eruptions typical of shield volcanism, known as Hawaiian eruptions . These eruptions, the least explosive of volcanic events, are characterized by the effusive emission of highly fluid basaltic lavas with low gaseous content . These lavas travel

9785-534: The walls of the tube insulate the lava within. Lava tubes can account for a large portion of shield volcano activity; for example, an estimated 58% of the lava forming Kīlauea comes from lava tubes. In some shield volcano eruptions, basaltic lava pours out of a long fissure instead of a central vent, and shrouds the countryside with a long band of volcanic material in the form of a broad plateau . Plateaus of this type exist in Iceland, Washington, Oregon, and Idaho;

9888-447: The western face of Kohala. Mauna Loa, an active volcano, has since repaired its flank. Marine geologist Tappin believes that a "future collapse on this volcano, with the potential for mega-tsunami generation, is almost certain." Kohala had two active rift zones , a characteristic common to Hawaiian volcanoes. The double ridge, shaped axially , was active in both the shield and postshield stages. The southeast rift zone passes under

9991-474: The wildlife population at Kohala and on the rest of the island was isolated from other species, as it was separated from the nearest major landmass by over 2,000 mi (3,200 km) of open water. The early colonizers of Kohala came by wind, storm or floating on the ocean. Successful colonizations occur on the magnitude of once every 35,000 years. The 2,000 successful ancestors that arrived at Kohala evolved into about 8,500 to 12,500 unique species, resulting in

10094-724: The world is the Hawaiian–Emperor seamount chain, a chain of hotspot volcanoes in the Pacific Ocean. The volcanoes follow a distinct evolutionary pattern of growth and death. The chain contains at least 43 major volcanoes, and Meiji Seamount at its terminus near the Kuril–Kamchatka Trench is 85 million years old. The youngest part of the chain is Hawaii, where the volcanoes are characterized by frequent rift eruptions, their large size (thousands of km in volume), and their rough, decentralized shape. Rift zones are

10197-686: The world with a permanent lava lake, which has been active since at least 1967, and possibly since 1906. Other volcanic centers include Menengai , a massive shield caldera, and Mount Marsabit in Kenya. Shield volcanoes are not limited to Earth; they have been found on Mars , Venus , and Jupiter's moon, Io . The shield volcanoes of Mars are very similar to the shield volcanoes on Earth. On both planets, they have gently sloping flanks, collapse craters along their central structure, and are built of highly fluid lavas. Volcanic features on Mars were observed long before they were first studied in detail during

10300-436: The world. These are eruptive features which occur along linear fissure vents and are distinguished from shield volcanoes by the lack of an identifiable primary eruptive center. Active shield volcanoes experience near-continuous eruptive activity over extremely long periods of time, resulting in the gradual build-up of edifices that can reach extremely large dimensions. With the exclusion of flood basalts, mature shields are

10403-780: Was born near Upolu Point , the northern tip of Kohala. The site is within Kohala Historical Sites State Monument . The original Kamehameha Statue stands in front of the community center in Kapaʻau , and replicas of the statue are found at Aliʻiōlani Hale in Honolulu , and in Emancipation Hall at the United States Capitol Visitor Center in Washington, D.C. Shield volcano A shield volcano

10506-552: Was measured to be 80,000 years in age. The samples have been treated with skepticism by the scientific community, and their ages have been directly challenged. The rocks collected from the west site have not been tested by subsequent experiments. The lava samples collected from the eastern site were allegedly found under a Mauna Loa lava flow, which had been previously dated to 187,000 years. The Kohala lava flows could be as young as 120,000 years although they may be even younger. In 2004, unidentified marine fossils were found at

10609-403: Was weakened by the collapse. As the dikes forced their way up, they formed fractures and faults parallel to the rift zone. The exertion caused by the dikes produced a series of faults along its length, forming horsts and grabens ( fault blocks ). Northeast of the Kohala summit, where the most rainfall occurs, the faulted structure prevents summit rainwater from naturally flowing northeast down

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