The Great Crack is one of the most conspicuous features of the Southwest Rift Zone of Hawaii’s Kilauea Volcano. (Halliday) It is an extensive network of cracks, fissures and cones. It spans 8 miles in length, measures 50 feet in width and plunges down to a depth of 66 feet.
Hawaiian Volcano Observatory geologists believe that the crack formed as magma intruded into the rift zone causing the surface to spread, not from the island falling apart. While the exact time of its formation remains uncertain, research indicates that it might have occurred gradually over time. (NPS)
In 1823, an eruption caused lava to surge out from the lower section of the Great Crack and flow for about 6 miles into the ocean, destroying one small coastal village at Mahuka Bay.
English missionary William Ellis witnessed the aftermath of the eruption. “Messrs (William) Ellis, (Asa) Thurston, (Artemas) Bishop and (Joseph) Goodrich made a tour round the island of Hawai‘i, examining its various districts, conversing with the natives, and preaching the gospel 130 different times.” (History of ABCFM) They were looking for suitable sites for mission stations.
Of this, Ellis wrote, “The people of Kearakomo also told us, that, no longer than five moons ago, Pele had issued from a subterranean cavern, and overflowed the low land of Kearaara, and the southern part of Kapapala.”
“The inundation was sudden and violent, burnt one canoe, and carried four more into the sea. At Mahuka, the deep torrent of lava bore into the sea a large rock, according to their account, near a hundred feet high, which, a short period before, had been separated by an earth quake from the main pile in the neighbourhood ….”
“We exceedingly regretted our ignorance of this inundation at the time we passed through the inland parts of the above-mentioned districts, for, had we known of it then, we should certainly have descended to the shore, and examined its extent and appearance.”
“We now felt convinced that the chasms we had visited at Ponahohoa, and the smoking fissures we afterwards saw nearer Kirauea, marked the course of a stream of lava, and thought it probable, that though the lava had burst out five months ago, it was still flowing in a smaller and less rapid stream.” (Ellis)
A hundred years later, geologist Harold Stearns officially named it the ‘Keaiwa Flow,’ which was a name the residents of Ka‘ū had been using informally back then. (NPS)
“The Keaiwa flow of 1823 from Kilauea welled up in the Great Crack and spread out seaward as a thin flow, in places only a few inches thick. The absence of cinders or driblet cones in or along the crack indicates that the usual fire fountains of Hawaii did not play during this eruption.”
“Lining the Great Crack in many places are lava balls that appear to be bombs, but that do not owe their form to projection.” (Stearns)
Beginning at roughly 2,300 feet in elevation, the lower extent of the Southwest Rift Zone is quite unlike any other on the island. Faulting activity here has consolidated into a feature named The Great Crack. It is just that, a single large crack that runs unbroken for more than 10 miles before finally reaching the coastline. (Coons)
“The Great Crack is one of a number of open cracks that fissure the southwest rift zone, a belt 1-2 miles wide extending southwestward from Kilauea to the sea.”
“Throughout most of its length the Great Crack has the general appearance of a steep-sided trench 20 to 30 feet wide. A few yards north of the head of the Keaiwa flow the crack breaks up into many smaller ones.”
“There are also graben areas [an elongated block of the earth’s crust lying between two faults and displaced downward] which seem to have been produced by the separation of the fissure into two cracks for a short distance and the later collapse of the narrow slices thus formed, with the subsidence of the magma.”
“In other places the graben is due to the collapse along the walls bordering the fissure when the region settled down after the extrusion of the lava. In a few places, especially near the sea, the Great Crack decreases in width to about 2 feet, and it finally dies out in echelon fashion at the coast. The cracks beyond the area of extravasation are only a few inches wide.”
“The Great Crack … differs from the others only in its continuity; it can be traced continuously for about 8 miles, and before it was buried by the flow of 1920 it must have been traceable still farther toward Halemaumau.”
“However, the mere fact that the Great Crack is continuous does not necessarily indicate that it was all opened at one time. There is ample evidence to show that it belongs to a system of fissures from which lava has poured out again and again.” (Stearns)
The Great Crack “is the result of crustal dilation from magmatic intrusions into the rift zone and not from the seaward movement of the south flank. There is no evidence that the Great Crack is getting bigger at this time or that the island is tearing apart along this seam.”
“Where the crack is narrow enough that opposing walls can be compared, matching features fit together like pieces of a jigsaw puzzle. This suggests that a simple widening caused the crack. Opposite walls also have no vertical offset, so south flank subsidence did not influence the formation of the crack.”
“The total breakaway of the south flank block of Kīlauea … is not taking place at this time.” (USGS)
Notable features in the Great Crack are caves. Most of the floor of the open crack is littered with breakdown, but there are occasional gaps where cave entrances and pit craters lead to greater depths within the Great Crack System. It is believed there are more than 20 of these.
“The National Park Service has acquired a nearly 2,000-acre Big Island property containing a chasm known as ‘The Great Crack.’ The oceanfront property adjacent to Hawaii Volcanoes National Park was purchased for $1.95 million in a recent foreclosure sale”.
“The park has been interested in the property northeast of Pahala for more than five decades, said Ben Hayes, the park’s director of interpretation.” (Associated Press, 2018)
The National Park is working to create a long-term plan for managing the Great Crack area. The park is exploring future public use options for these areas, with a community meeting in Fall 2023 to learn from local residents about the site’s resources and past uses. (NPS)
Leave your comment here: