The Hawai’ian-Emperor Seamount Chain
The Hawai’ian Islands are the southern and easternmost of a string of islands and seamounts that stretch from their location in the north-central Pacific Ocean to the Bering Sea. The entire string is called the Hawai’ian–Emperor seamount chain. A seamount is a mountain, in this case, a volcano, that does not rise above sea level
The current Hawai’ian island chain stretches from the Big Island in the east, 1500 miles to Kure Atoll in the west. Many of the older islands/atolls, such as Kure are coral reefs that have grown on top of an extinct volcano after it moved off the hotspot. As they continue to move north with the Pacific plate, the coral will die in the colder waters, and the islands will erode to become seamounts. The island chain includes Midway, the only island in the chain that is not part of the State of Hawai’i.
All the mounts are volcanic, having formed over a hotspot in the magma below the crust. The magma heated at this hotspot forces its way up through the oceanic crust of the Pacific Tectonic Plate. The result is a string of volcanoes that form over the hot spot and become extinct as the plate moves.
Geologists are uncertain how or why hotspots form, though there are several hypotheses. Unlike the volcanoes of such things as the Ring of Fire around the Pacific Plate, they are independent of tectonic plate boundaries. Two other well-known locations of hotspots are the Yellowstone Caldera and Iceland.
Iceland is different, as it is also part of the mid-Atlantic ridge, which is a plate boundary. This confuses the geology of Iceland a little, but the presence of both the ridge and the hotspot explain why it’s a high island, while the rest of the Atlantic ridge is well below sea level. All three of these hotspots are volcanically active.
Two other well-known locations of hotspots are the Yellowstone Caldera and Iceland.
Iceland is different, as it is also part of the mid-Atlantic ridge, which is a plate boundary. This confuses the geology of Iceland a little, but the presence of both the ridge and the hotspot explain why it’s a high island, while the rest of the Atlantic ridge is well below sea level. All three of these hotspots are volcanically active.
About 700 miles west of Kure Atoll, the Hawai’ian-Emperor chain turns northward. The chain stretches an additional 1500 miles to the Bering sea for a total of about 35000 miles. It’s currently uncertain whether the hotspot moved or the Pacific plate changed direction about 50 million years ago to form the bend.
The north-trending seamount chain is called the ‘Emperor’ chain as most of the seamounts are named after former Emperors of Japan.
The Big Island of Hawai’i, which is still over the hotspot, is only about a million years old and is still building. The oldest of the seamounts, the far northern Meiji Guyot, is between 85 and 81 million years old, which places it in the mid to late Cretaceous. Because the hotspot’s age is uncertain, it’s uncertain whether there were older seamounts that have already been subducted, or whether Meiji Guyot is the first of the chain to form over the hotspot.
Unless the Pacific plate changes direction, the seamounts and islands will eventually be subducted at the Kuril-Kamchatka Trench, located between the Kamchatka Peninsula and Meiji Guyot. We can expect the Big Island to undergo subduction in about 90 million years.
If you’re interested in volcanoes and undersea geology, there’s plenty to research left to do on these geologic features.
There are currently four active volcanoes on the Island of Hawai’i and one more on Maui. Between 1912 and 2012, there were almost 50 Kīlauea eruptions, 12 Mauna Loa eruptions, and one Hualālai intrusion of magma, a sort of low-key eruption.
Mauna Kea last erupted about 4,000 years ago. Kama‘ehuakanaloa (formerly Lō‘ihi Seamount), the submarine volcano located off the south coast of Kīlauea, erupted twice between 1950 and 1996.
The Island of Maui has one active volcano, Haleakalā, which has erupted at least 10 times during the past 1,000 years.
Kīlauea
Kīlauea, the youngest and most active volcano on the Island of Hawai‘i, erupted almost continuously from 1983 to 2018 at Pu‘u‘ō‘ō and other vents along the volcano’s East Rift Zone. From 2008 to 2018, there was a lava lake within the Halema‘uma‘u crater at the volcano’s summit. In 2018, Kīlauea experienced the largest lower East Rift Zone eruption and summit collapse in at least 200 years. Several summit eruptions since December 2020 have generated lava lakes that have been slowly filling in the collapsed area, including the Halema‘uma‘u crater. The most recent eruption as of August 2023 was September 29, 2021 – December 13, 2022.
Kīlauea appears as a bulge on the southeastern flank of Mauna Loa. For many years it was thought to be a satellite, not a separate volcano. New research shows that Kīlauea has its own magma system, more than 60 km deep in the earth.
Hawaiians used the word Kīlauea only for the summit caldera, but geologists and popular usage have used the name for the entire volcano.
About 90 percent of Kīlauea is covered with lava flows less than 1,100 years in age.
Mauna Loa
Mauna Loa is the largest volcano on Earth. Mauna Loa’s submarine flanks descend to the seafloor an additional 5 km (16,400 ft), and the seafloor is pushed down by Mauna Loa’s great mass another 8 km (26,200 ft). This makes the volcano’s summit about 17 km (55,700 ft) above its base. The summit of Mount Everest is only 29,032 feet from its base, a difference of over 26,000 feet.
Mauna Loa makes up about half of the Island of Hawai‘i and by itself amounts to about 85 percent of the area of all the other Hawaiian Islands combined.
In addition to being the largest, Mauna Loa is among Earth’s most active volcanoes, with 34 eruptions since 1843, its first well-documented eruption.
Hualālai
Hualālai, the third most active volcano is comparatively inactive. It has erupted three times in the past 1,000 years. 1801 was the most recent eruption. The lava flow from that eruption is now covered by the Kona International Airport. Lava flows less than 5,000 years old cover about 80 percent of Hualālai.
Hualālai is considered to be in the post-shield stage. Six vents erupted lava between the late 1700s and 1801. The Kona International Airport at Keahole, located only 11 km (7 mi) north of Kailua-Kona, is built atop a recent large lava flow. The oldest dated rocks are from about 128,000 years ago and Hualālai probably grew above sea level before 300,000 years ago. The volume of Hualālai is 12,400 km3 (2,975 mi3). Its area is 751 km2 (290 mi2).
Though Hualālai is not nearly as active as Mauna Loa or Kīlauea, geologic mapping of the volcano shows that 80 percent of Hualālai’s surface has been covered by lava flows in the past 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 more than 6,200 earthquakes rattled the area around Hualālai Volcano for more than a month. The earthquakes were most likely caused by an intrusion of magma beneath the volcano. Two large earthquakes (each about magnitude 6.5) destroyed houses, water tanks, stone fences, and roadways. For these reasons, Hualālai is considered a potentially dangerous volcano that is likely to erupt again.
Mauna Kea
Mauna Kea is the highest volcano on the Island of Hawai‘i. It has not erupted for between 4,500 and 6,000 years. Glaciers appeared on the summit during the recent ice ages, the only known Hawaiian glaciers.
Kama‘ehuakanaloa
Kama‘ehuakanaloa (formerly Lō‘ihi Seamount), is the only known active Hawaiian submarine volcano. It is about 22 miles southeast of Hawai’i. It last erupted in 1996. The volcano’s summit is just over 3,179 ft below sea level.
This seamount rises to 975 m (3,189 ft) below sea level. It generates frequent earthquake swarms with a recent intense swarm in 1996, with more than 4,000 small quakes. No eruptions have been observed, but the results of them have been studied and they are explosive. It is considered to be between the pre-shield and shield stages. Kama‘ehuakanaloa’s volume is 1,700 km3 (407 mi3), and.
The summit of the submarine volcano has a caldera about 2.8 km (1.7 mi) wide and 3.7 km (2.3 mi) long.
Volcanologists don’t know for certain when or if Kama‘ehuakanaloa will breach sea level. If it continues to grow at its past growth rate of 5 m (16.4 ft) per 1000 years it should breach the waves in about 200,000 years.
Haleakalā
Haleakalā is the active volcano on Maui. It was most recently between about 400 and 600 years ago. It has erupted about 10 times in the last 1,000 years. Haleakalā’s last erupted between 1480 and 1600 C.E., and it is expected to erupt in the future. The volcano’s volume is about 30,000 km3 (7,200 mi3), about 97% of the volume below sea level. Its area is 1,470 km2 (570 mi2. The volcano is in its post-shield stage.
The large Haleakalā Crater occupies the summit. The crater opens at the northwest and southeast corners. These openings form large valleys that drain to the coasts.
The oldest lava flow on the volcano is about 1.1 million years old. The volcano began growing about 2 million years ago.
More Information
If you’re interested in more information about the volcanoes of Hawai’i, you can start by visiting the US Geological Survey’s Volcano Observatory website “Active Volcanoes in Hawai’i.”
https://www.usgs.gov/observatories/hvo/active-volcanoes-hawaii