May 24 marks the one-year anniversary of key events in the 2018 Kilauea eruption.
Its most notable event? The reactivation of fissure 8 with intermittent spattering while fissures 7 and 21 were producing two ‘a‘ā flows.
It is also the 50th anniversary of another important event on Kīlauea’s East Rift Zone: the start of the 1969‒1974 Mauna Ulu eruption.
Fifty years ago, on May 24, 1969, the opening fissure of the Mauna Ulu eruption broke ground where Kīlauea’s east rift and the Koa‘e fault zone intersect. This fissure behaved similarly to fissures 17, 20, and 22 of the 2018 eruption with 30-m- (100-ft-) tall lava fountains emerging from a linear crack. This style of eruption is classic to Hawaii and is thus called “Hawaiian fountaining” in volcanology textbooks around the world.
At Mauna Ulu, the fissure system stretched 4.5 km (3 mi) from east to west and cut straight through ‘Ālo‘i and Ala‘e pit craters within Hawaiʻi Volcanoes National Park.
On the first day of the Mauna Ulu eruption, the western fountaining zone erupted for 18 hours. The eastern zone erupted for 36 hours, but not much is known about that activity because the Chain of Craters Road was cut by the western fountains, making the eastern fountains visible only in the far distance.
The five-year-long Mauna Ulu eruption was preceded by a series of East Rift Zone fissure eruptions that occurred in 1960, 1961, 1962, 1963 (2), 1965 (2), 1968 (2), and February 1969, each lasting between 1 and 15 days.
This eruption produced invaluable scientific advancements in volcano science, including an improved scientific understanding of how pāhoehoe and ‘a‘ā form.
Mauna ulu provided the first detailed observations of pillow lava forming underwater. The development of large lava flow fields, the formation of lava tubes, and the origin of tree molds were also documented.
The Mauna Ulu eruption was the largest, most voluminous, and best documented eruption recorded at Kīlauea in the 20th century, until 1983 when the next long-lived eruption began.