| Hualālai | |
|---|---|
 North face of Hualālai as seen from Waimea |
|
| Elevation | 8,271 ft (2,521 meters)[1] |
| Location | Hawaiʻi, USA |
| Range | Hawaiian Islands |
| Prominence | 2,473 m[1] |
| Coordinates | 19°41′32″N 155°52′02″W / 19.69222°N 155.86722°W[1] |
| Topo map | USGS Hualālai |
| Type | Shield volcano |
| Volcanic arc/belt | Hawaiian-Emperor seamount chain |
| Age of rock | 128,000 years[1] |
| Last eruption | 1801[1] |
| Pronunciation | Hawaiian: [huəˈlaːlei] |
Hualālai (pronounced [huəˈlaːlei] in Hawaiian) is a dormant shield volcano on the island of Hawaiʻi in the Hawaiian Islands. Its peak is 8,271 ft (2,521 m) above sea level. Hualālai is one of five volcanoes on Hawaii island and it lies roughly due west of the saddle between the much higher volcanoes Mauna Kea and Mauna Loa. Hualālai forms the backdrop to the town of Kailua-Kona, which is built on the southwestern slope of this mountain, where most Kona coffee is grown.
Contents |
Structure
The Island of Hawaiʻi is built from five separate shield volcanoes that erupted somewhat sequentially, one overlapping the other. These are (from oldest to youngest):
- Kohala (extinct)
- Mauna Kea (dormant)
- Hualālai (dormant)
- Mauna Loa (active, partly within Hawaiʻi Volcanoes National Park)
- Kīlauea (very active; part of Hawaiʻi Volcanoes National Park)
Hualālai is built from a well-defined rift zone that trends approximately N50°W across its summit and a less well-defined rift zone that trends northward from a point 3 mi east of the summit.[2] The oldest dated rocks on the mountain surface are about 128,000 years before present (0.1 Mya). It is estimated that the volcano appeared above sea level some 300,000 years ago (0.3 Mya; USGS).[1]
Over 100 cinder and spatter cones are arranged along the rift zones. There is no summit caldera, just a collapse crater (~ 0.3 mile across) at the top of a small lava shield.[1] Much of the southern slope (above the town of Kailua-Kona) consists of lava flows covered by a layer of volcanic ash from 10 cm (a few inches) to a meter (3 ft) thick. Hualālai appears to have entered the late stage of the eruptive cycle of Hawaiian volcanoes
Hualalai is a shield volcano located on Hawaii. The summit of Hualalai is 2,521 m. (8,271 ft.) above sea level.[1] This volcano is farthest west of the five volcanoes on Hawaiian. The last eruption of Hualalai was in 1800-1801 along the northwest rift zone. When it erupted six vents opened up. It is on a hot spot in the middle of the Pacific plate. Hualalai grew above sea level approximately 300,000 years ago[2] and is in the post-shield stage of its development.[1]
Recent eruptions
Six vents erupted lava between the late 1700s and 1801, two of which generated lava flows that poured into the sea along the west coast of the island. The Keāhole-Kona Airport, located only 11 km (7 mi) north of Kailua-Kona, is built atop the smaller Huehue flow (1801) just north of Keāhole Point.[3]
Although Hualālai is not nearly as active as nearby Mauna Loa or Kīlauea, geologic mapping of the volcano shows that 80 percent of Hualālai's surface is covered by lava flows no older than about 5,000 years. In the past few decades, when most of the resorts, homes, and commercial buildings were built on the flanks of Hualālai, earthquake activity beneath the volcano has been low. In 1929, however, an intense swarm of earthquakes lasting more than a month was most likely caused by magma rising to near the surface. For these reasons, Hualālai is considered a potentially dangerous volcano that is likely to erupt again sometime in the next 100 years.[1]
Lava stratigraphy
The USGS has divided the exposed lava flows and tephra erupted by Hualalai volcano during the last 112,000 years into 419 rock units of eight chronostratigraphic age groups. These are summarised in the table below:
| Age Group | Age (years B.P.) | Rock type | Surface area (percent) | Number of rock units | Location of exposures | Comments |
|---|---|---|---|---|---|---|
| 8 | less than 200 | alkali basalt | 6 | 3 | northwest flank | Vent cinder deposits with black pahoehoe basalt lava flows formed during AD 1800-1801 eruption. Five vents along NW rift zone. Abundant xenoliths of ultramafic plutonic rocks. |
| 7 | 200-700 | alkali basalt | 3 | 4 | southern flank | Vent lava spatter and lava flows, cinders and tuff at Waha Pele. Spatter cone erupted pahoehoe and aa basalt lava flows. Cone collapsed causing violent phreatic eruptions of tuff. Lava flow eruption resumed building larger cone, with eruption of long aa lava flows. |
| 6 | 750-1,500 | alkali basalt | 8 | 14 | mostly central summit area and southeast flank | Dark grey to black vent lava spatter (including a 650 metre long spatter rampart), cinders, aa and pahoehoe basalt lava flows, including Hualalai's longest lava flow (22 km). Collapse of vents produced pit craters. Hawaiian, Strombolian and sub-Plinian activity. |
| 5 | 1,500-3,000 | alkali basalt | 38 | 49 | mostly northern flank | Spatter deposits, aa and pahoehoe basalt lava flows. Very active 2,400-1,900 years B.P. |
| 4 | 3,000-5,000 | alkali basalt | 25 | 98 | mostly northern flank and summit | Spatter deposits, aa and pahoehoe basalt lava flows. |
| 3 | 5,000-10,000 | alkali basalt with minor amounts of picritic basalt, hawaiite and ankaramite | 15 | 185 | mostly southern flank and summit | Spatter deposits, extensively weathered aa and pahoehoe lava flows. |
| 2 | 10,000-25,000 | alkali basalt with minor amounts of picritic basalt, hawaiite and ankaramite | 5 | 63 | northeastern and southwestern flanks | Lava spatter, cinders, extensively weathered aa and pahoehoe lava flows and palagonite tuff. Spatter and cinders contain abundant xenoliths of mafic and ultramafic plutonic rocks. |
| 1 | more than 100,000 | trachyte | less than 1 | 3 | northeastern flank | Trachyte cone of Puu Waawaa (current prominence approximately 430 metres). Block and aa trachyte lava flow of Puu Anahulu and trachyte pyroclastic deposits. 5.5 km3 in volume, the largest-volume single eruption on Hawaii (Big island). K-Ar age is 106,000 ± 6,000 years B.P. |
References
- ^ a b c d e f g h i j "Hualālai, Hawaiʻi's Third Active Volcano". USGS. http://hvo.wr.usgs.gov/volcanoes/hualalai/main.html.
- ^ a b Macdonald, G.A.; A. T. Abbott (1970). Volcanoes in the Sea. Univ. of Hawaiʻi Press. pp. 441.
- ^ "Fishponds versus lavaflows". USGS. 1997. http://hvo.wr.usgs.gov/volcanowatch/1997/97_07_25.html.
- ^ Moore. R. B. and Clague, D.A. (1991) Geologic Map of Hualalai Volcano, Hawaii; USGS Miscellaneous Investigations Series, Map I-2213, 1:50,000
External links
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