Kīlauea Iki

Early warning signs of the impending eruption included outward tilting at the summit region and increased seismicity.[4][3][8] Tiltmeter measurements between November 1957 and February 1959 indicated that magma was migrating towards the summit, causing swelling of the ground surface.[4] Swelling ceased and deflation of the summit began after several earthquakes occurred on February 19, 1959.[4] Slow deflation continued until a swarm of earthquakes in mid-August 1959 led to resumption of rapid swelling that continued until the eruption in November.[4][8] Most of these earthquake swarms were at a depth of 40-60 km and likely related to upward magma movement from the mantle.[3] By early November, more than 1,000 earthquakes were being recorded each day and tiltmeter measurements indicated swelling 3 times faster than previous rates.[4][8]

Lava fountaining at Kilauea Iki on December 11th, 1959

Lava fountaining is characteristic of Hawaiian eruptions and the 1959 eruption of Kilauea Iki produced some of the highest lava fountains ever observed in Hawaii.[3][9] At the beginning of the eruption, the fountain height was only 30 m, but this increased over the next several days to between 200 and 300 m.[5] On November 21, the fountain went from 210 meters tall to a few gas bubbles in less than 40 seconds.[5] Some of the fountains were extraordinarily high, with the 15th episode producing a fountain reaching nearly 580 m (1,900 ft), among the highest ever recorded.[5][9] After the end of each eruption episode, lava drained back into the vent which may have acted as a coolant for the underlying material, resulting in the triggering of the next episode of lava fountaining.[10]

Magma Budget from USGS

Tourists trekking along a well-worn path through the crater landscape, May 1999

Lava drainback is common during eruptions at Kilauea and occurs when magma erupts at the surface, forming a lava lake and then draining back below ground.[11][8] During the Kilauea Iki eruption, the level of the lava lake would rise until it reached the erupting vent partway up the crater wall, where lava drainback would begin.[6][4][11] The first episode had 31 million cubic meters of lava flow into Kīlauea Iki with 1 million cubic meters draining back.[8] During the following episodes, a total of 71 million cubic meters of lava was ejected during a month-long eruption that stopped on December 20, 1959.[8] Only 8 million cubic meters of lava remained, with 63 million cubic meters of lava draining back into the Kīlauea magma reservoir.[8] Often the lava drainback had a higher rate of flow than the eruptions.[8]

With every filling and draining of the lava lake, a 'black ledge' was formed along the rim of the crater which marked the level of the lava lake during each eruption episode.[6][8] During lava drainbacks, a giant counter-clockwise whirlpool would form.[4]

Samples collected from the first episode of the eruption were composed of two different kinds of magma.[3][12] The first variant was identical to previous magmas erupted in the 1954 Kilauea caldera eruption and the second variant had a composition different from anything seen at previous eruptions, with a high ratio of CaO to MgO.[3] Subsequent eruption episodes produced samples that were a mixture of the two variants plus some additional amount of olivine.[12] The reason for two different magma compositions may be two magma storage areas beneath Kilauea Iki that had higher olivine concentrations at the bottom.[12] At the beginning of the eruption, both magma sources provided material to the surface, while later eruption episodes at the single vent on the west side of the caldera contained a mixture of the two magmas.[12][3] Additionally, the later eruption episodes were sourced from deeper sections of the magma chambers, resulting in higher concentrations of olivine.[12][10]