The island of Hawaii (commonly called the "Big Island") is the currently active volcanic center of the
Hawaiian Islands formed over the
Hawaii hotspot. Two of the active volcanoes on the Big Island are
Kīlauea and
Mauna Loa with a newer submarine volcano forming the
Kamaʻehuakanaloa Seamount (formerly Lōʻihi) to the southeast of the island. Continued growth of the southeastern part of the island is accompanied by major slumping and southeastward movement of the flanks of the two volcanoes. This flank displacement is linked to extension within the rift zones associated with both of the active volcanoes, the Mauna Loa and Kīlauea rifts. From the interpretation of
seismic reflection data, it has been proposed that the southeastward displacement takes place on a
decollement surface near the top of the
oceanic crust. The slumping is thought to affect only the upper part of the flank as the amount of shortening observed in the toe thrust zone is much larger than that observed in the extensional faults associated with the slumps, but matches well with estimates of extension within the volcanic rift systems.
Hilina Slump The Hilina Slump is the largest of the active slumps around the Hawaiian islands. The '' to the slump is formed by the Hilina extensional fault system, which is known to have moved in both the 1868 event and the
1975 Kalapana earthquake.
Earthquake A firsthand description of the events was written by
Frederick S. Lyman, a goat and sheep rancher at Keaīwa near the epicenter of the events. A sequence of
foreshocks began on March 27, with tremors every few minutes. They increased steadily in intensity, including one on March 28 that had an estimated magnitude of 7.1. The sequence continued until 4 p.m. on April 2, when the mainshock occurred. and was probably triggered by the earlier event. The aftershock sequence has continued for over 140 years until the present day. The aftershock frequency fits a modified
Omori (power law) for the first few decades and an exponential function thereafter. == Damage ==