Hawaiʻi is an island state built completely of volcanoes old and new. Hot and fluid magma circulating in the planet’s mantle seeps up to and through the crust as a plume and emerges on the seafloor in the middle of the Pacific Plate, where it methodically builds up a shield volcano. The plate is moving north/northwest and subducting under Japan/Russia at a rate of about 5-10 centimeters a year. So, like a great, slow, patient conveyor belt, the plate drifts over the “hot spot” of the mantle plume and volcanoes are built, one after the other.
Eventually the drift of the plate pulls the volcano off of the hot spot that formed it, and eruptions gradually cease. At that point, erosion and settling pick up speed and, just as steadily and constantly, the volcano is worn down to sea level, and then under sea level, too. Formerly high-standing volcanoes that are now under the waves are called “seamounts”, and they stretch nearly to Japan on the northeast end of the Hawaiian chain. The line of old seamounts and young volcanoes is nearly 4,000 miles long, and at the south/southeast end you find the youngest on Hawaiʻi Island, home to Kīlauea and Mauna Loa volcanoes. Jump just one island back to Maui, and there stands Haleakalā. These three volcanoes have been very active in the recent past and all three are within national park boundaries.
When the first people arrived to the present day Main Hawaiian Islands, those islands which are the youngest and tallest above the waves, they employed their immense powers of observation to note that the chain had an older/younger, smaller/larger flow to it. Stories rose from this understanding, powerful myths and legends about Pele, the volcano deity, who travelled the islets and islands from northeast to southwest, finally settling into the great summit caldera of Kīlauea.
Kīlauea is the youngest of the currently active Hawaiian volcanoes that has built above sea level (the steadily growing Loʻihi Seamount off of the southeast coast of Hawaiʻi Island still has a way to go before its summit emerges into the air). As of this writing, a Kīlauea summit eruption that began in September, 2021, is ongoing, albeit in fits and starts. In 2018, an eruption along the volcano’s Lower East Rift Zone on the flank rearranged the topography of much of the Puna District and displaced about 2,000 residents. For a long stretch of human years, 1983 to 2018, it was possible, and common, to walk or hike out to the slow-moving lava flows sliding down to the sea from the Puʻu ʻŌʻō vent on the volcano’s East Rift Zone flank. The summit of Kīlauea is contained within Hawaiʻi Volcanoes National Park and is generally accessible unless there is an immediate threat there. Volcanologists rate the overall threat potential from Kīlauea as “very high”.
The vast curve of Mauna Loa dominates the views from East and South Hawaiʻi. It, alone, makes up over half of Hawaiʻi Island. When measured from the seafloor, Mauna Loa’s actual height is nearly 56,000ft. Its last eruption was in November of 2022, and its eruptive history is well enough understood to also place it in the “very high” threat potential category. Eruptions of Mauna Loa are big events, effusing many times the volume of lava produced at Kīlauea, and sometimes at startling speeds. As Hawaiʻi Island has developed, many more residents are potentially impacted by the next eruption of Mauna Loa, so volcanologists are continuously monitoring it via sensors on the ground and satellite data.
Haleakalā Volcano, the larger of the two volcanoes that make up the island of Maui, has had at least 10 eruptions in the past 1,000 years, but the last eruption is thought to have happened sometime between A.D. 1400-1600. That lava flow can be visited in the Natural Area Reserve along the southern coast of the island. A common misconception is that there is a crater at the summit of Haleakalā, the way there is at Mauna Loa and Kīlauea volcanoes. However, erosion has long since removed the original summit, and what remains is a Z-shaped erosional valley with steep walls and cinder cones studding its floor. While the volcano is being monitored at all times, the current alert level is green/normal, with no indications of change any time soon.
Questions about the geology of Hawaiian volcanoes? Email
Volcano and geology books are here: https://shop.hawaiipacificparks.org/collections/geology
Hawaiʻi maps are here: https://shop.hawaiipacificparks.org/collections/maps
