Kamaʻehuakanaloa Seamount (previously known as Lōʻihi) is an active submarine volcano about off the southeast coast of the island of Hawaii. The top of the seamount is about below sea level. This seamount is on the flank of Mauna Loa, the largest subaerial active shield volcano on Earth. Kamaʻehuakanaloa is the newest volcano in the Hawaiian–Emperor seamount chain, a string of volcanoes that stretches about northwest of Kamaʻehuakanaloa. Unlike most active volcanoes in the Pacific Ocean that make up the active plate margins on the Pacific Ring of Fire, Kamaʻehuakanaloa 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, Kamaʻehuakanaloa is the only Hawaiian volcano in the deep submarine preshield stage of development.
Kamaʻehuakanaloa began forming around 400,000 years ago and is expected to begin emerging above sea level about 10,000–100,000 years from now. At its summit, Kamaʻehuakanaloa Seamount stands more than above the seafloor, making it taller than Mount St. Helens was before its catastrophic 1980 eruption. A diverse microbial community resides around Kamaʻehuakanaloa's many hydrothermal vents.
In the summer of 1996, a swarm of 4,070 earthquakes was recorded at Kamaʻehuakanaloa. At the time this was the most energetic earthquake swarm in Hawaii recorded history. The swarm altered of the seamount's summit; one section, Pele's Vents, collapsed entirely upon itself and formed the renamed Pele's Pit. The volcano has remained relatively active since the 1996 swarm and is monitored by the United States Geological Survey (USGS). The Hawaii Undersea Geological Observatory (HUGO) provided real-time data on Kamaʻehuakanaloa between 1997 and 1998. Kamaʻehuakanaloa's last known eruption was in 1996, before the earthquake swarm of that summer.
Naming The name Kamaʻehuakanaloa is a Hawaiian language word for "glowing child of Kanaloa", the god of the ocean. This name was found in two Hawaiian mele from the 19th and early twentieth centuries based on research at the Bishop Museum and was assigned by the Hawaiʻi Board on Geographic Names in 2021 and adopted by the U.S. Geological Survey. From 1955 to 2021 the seamount was called "Lōʻihi", the Hawaiian word for "long", describing its shape. The change to Kamaʻehuakanaloa was made in an effort to be more culturally appropriate given native Hawaiian traditions for naming.
Characteristics Geology
Kamaʻehuakanaloa is a seamount, or underwater volcano, on the flank of Mauna Loa, the Earth's tallest shield volcano. It is the newest volcano produced by the Hawaiʻi hotspot in the extensive Hawaiian–Emperor seamount chain. The distance between the summit of the older Mauna Loa and the summit of Kamaʻehuakanaloa is about , which is, coincidentally, also the approximate diameter of the Hawaiʻi hotspot. Kamaʻehuakanaloa consists of a summit area with three pit craters, a long rift zone extending north from the summit, and a long rift zone extending south-southeast from the summit.
The summit's pit craters are named West Pit, East Pit, and Pele's Pit. Pele's Pit is the youngest of this group and is located at the southern part of the summit. The walls of Pele's Pit stand high and were formed in July 1996 when its predecessor, Pele's Vent, a hydrothermal field near Kamaʻehuakanaloa summit, collapsed into a large depression. The thick crater walls of Pele's Pit – averaging in width, unusually thick for Hawaiian volcanic craters – suggest its craters have filled with lava multiple times in the past.
Kamaʻehuakanaloa's north–south trending rift zones form a distinctive elongated shape, from which the volcano's earlier Hawaiian name "Lōʻihi," meaning "long", derives. The north rift zone consists of a longer western portion and a shorter eastern rift zone. Observations show that both the north and south rift zones lack sediment cover, indicating recent activity. A bulge in the western part of the north rift zone contains three cone-shaped prominences.
Until 1970, Kamaʻehuakanaloa was thought to be an inactive volcano that had been transported to its current location by sea-floor spreading. The seafloor under Hawaii is years old and was produced at the East Pacific Rise, an oceanic spreading center where new sea floor forms from magma that erupts from the mantle. New oceanic crust moves away from the spreading center. Over a period of years, the sea floor under Hawaii moved from the East Pacific Rise to its present location west, carrying ancient seamounts with it. When scientists investigated a series of earthquakes off Hawaii in 1970, they discovered that Kamaʻehuakanaloa was an active member of the Hawaiian–Emperor seamount chain.
Kamaʻehuakanaloa is built on the seafloor with a slope of about five degrees. Its northern base on the flank of Mauna Loa is below sea level, but its southern base is a more substantial below the surface. Thus, the summit is above the seafloor as measured from the base of its north flank, but high when measured from the base of its southern flank. Kamaʻehuakanaloa is following the pattern of development that is characteristic of all Hawaiian volcanoes. Geochemical evidence from Kamaʻehuakanaloa's lavas indicates that Kamaʻehuakanaloa is in transition between the preshield and shield volcano stage, providing clues to the early development of Hawaiian volcanoes. In the preshield stage, Hawaiian volcanoes have steeper sides and a lower level of activity, producing an alkali basalt lava. Continued volcanism is expected to eventually give birth to an island at Kamaʻehuakanaloa. It experiences frequent landslides; the growth of the volcano has destabilized its slopes, and extensive areas of debris inhabit the steep southeastern face. Similar deposits from other Hawaiian volcanoes indicate that landslide debris is an important product of the early development of Hawaiian volcanoes. Kamaʻehuakanaloa is predicted to rise above the surface in 10,000 to 100,000 years.
Age and growth
Radiometric dating was used to determine the age of rock samples from Kamaʻehuakanaloa. The Hawaii Center for Volcanology tested samples recovered by various expeditions, notably the 1978 expedition, which provided 17 dredge samples. Most of the samples were found to be of recent origin; the oldest dated rock is around 300,000 years old. Following the 1996 event, some young breccia was also collected. Based on the samples, scientists estimate Kamaʻehuakanaloa is about 400,000 years old. The rock accumulates at an average rate of per year near the base, and near the summit. If the data model from other volcanoes such as Kīlauea holds true for Kamaʻehuakanaloa, 40% of the volcano's mass formed within the last 100,000 years. Assuming a linear growth rate, Kamaʻehuakanaloa is 250,000 years old. However, as with all hotspot volcanoes, Kamaʻehuakanaloa's level of activity has increased with time; therefore, it would take at least 400,000 years for such a volcano to reach Kamaʻehuakanaloa's mass. As Hawaiian volcanoes drift northwest at a rate of about a year, Kamaʻehuakanaloa was southeast of its current position at the time of its initial eruption.
Activity Kamaʻehuakanaloa is a young and fairly active volcano, although less active than nearby Kīlauea. In the past few decades, several earthquake swarms have been attributed to Kamaʻehuakanaloa, the largest of which are summarized in the table below. The volcano's activity is now known to predate scientific record keeping of its activity, which commenced in 1959. Most earthquake swarms at Kamaʻehuakanaloa have lasted less than two days; the two exceptions are the 1990-1991 earthquake, lasting several months, and the 1996 event, which was shorter but much more pronounced. The 1996 event was directly observed by an ocean bottom seismometer (OBS), allowing scientists to calculate the depth of the earthquakes as to below the summit, approximating to the position of Kamaʻehuakanaloa's extremely shallow magma chamber. This is evidence that Kamaʻehuakanaloa's seismicity is volcanic in origin.
The low-level seismic activity documented on Kamaʻehuakanaloa since 1959 has shown that between two and ten earthquakes per month are traceable to the summit. Earthquake swarm data have been used to analyze how well Kamaʻehuakanaloa's rocks propagate seismic waves and to investigate the relationship between earthquakes and eruptions. This low level activity is periodically punctuated by large swarms of earthquakes, each swarm composed of up to hundreds of earthquakes. The majority of the earthquakes are not distributed close to the summit, though they follow a north–south trend. Rather, most of the earthquakes occur in the southwest portion of Kamaʻehuakanaloa. The largest recorded swarms took place on Kamaʻehuakanaloa in 1971, 1972, 1975, 1991–92 and 1996. The nearest seismic station is around from Kamaʻehuakanaloa, on the south coast of Hawaii. Seismic events that have a magnitude under 2 are recorded often, but their location cannot be determined as precisely as it can for larger events. In fact, HUGO (Hawaii Undersea Geological Observatory), positioned on Kamaʻehuakanaloa's flank, detected ten times as many earthquakes as were recorded by the Hawaiian Volcano Observatory (HVO) seismic network.
1996 earthquake swarm + Major events Year(s) Summary Evidence of eruption in early 1996, and large, well-recorded earthquake swarm in the summer. Started on February 25, 1996, and lasted until August 9, 1996. An Ocean Bottom Observatory (OBO) device positioned on the seamount to track a recent earthquake swarm collected evidence of deflation, possibly due to magma withdrawal. Possible eruption, occurred on September 20, 1986 (one day). Nine events of magnitude 3 or greater, measuring between 3.0 and 4.2, were recorded from November 11, 1984, to January 21, 1985. Eruption possible, but uncertain. Prominent earthquake swarm from August 24, 1975, to November 1975. Possible eruption from September 17, 1971, to September 1972. Dates for older eruptions retrieved through Isotope dating. Eruption uncertain. An earthquake swarm on Kamaʻehuakanaloa in 1952 was the event that first brought attention to the volcano, previously thought extinct. Confirmed ancient eruption Confirmed ancient eruption Confirmed ancient eruption, most likely on the east flank This table indexes only possible volcanic eruptions and major events. Kamaʻehuakanaloa has also been the site of multiple earthquake swarms occurring on a nearly semi-annual basis.
The largest amount of activity recorded for the Kamaʻehuakanaloa seamount was a swarm of 4,070 earthquakes between July 16 and August 9, 1996. This series of earthquakes was the largest recorded for any Hawaiian volcano to date in both amount and intensity. Most of the earthquakes had moment magnitudes of less than 3.0. "Several hundred" had a magnitude greater than 3.0, including more than 40 greater than 4.0 and a 5.0 tremor.
The final two weeks of the earthquake swarm were observed by a rapid response cruise launched in August 1996. The National Science Foundation funded an expedition by University of Hawaiʻi scientists, led by Frederick Duennebier, that began investigating the swarm and its origin in August 1996. The scientists' assessment laid the groundwork for many of the expeditions that followed. Follow-up expeditions to Kamaʻehuakanaloa took place, including a series of crewed submersible dives in August and September. These were supplemented by a great deal of shore-based research. Fresh rock collected during the expedition revealed that an eruption occurred before the earthquake swarm.