1959 Kīlauea Iki Eruption
The 1959 eruption of Kīlauea Iki Crater was a relatively short-lived event and produced some of Kīlauea's most spectacular lava fountains of the 20th century. Most importantly, the eruption provided some of the first measurable data about the magma reservoir system at Kīlauea.
Earthquake swarms & summit tilt precede eruption.
Three months before the Kīlauea Iki eruption, between August 14 and 19, 1959, a swarm of deep earthquakes was recorded on the seismographs at the Hawaiian Volcano Observatory. The earthquakes were located about 55 km (35 mi) below the volcano. By October, tilt surveys of the caldera, using the new water-tube tiltmeter network, indicated that the summit reservoir of Kīlauea was beginning to inflate with new magma. Scientists later concluded that magma began its upward journey during the August swarm from about 55 km (35 mi) below the volcano.
Another series of earthquakes—shallow tiny events beneath the caldera—began in mid-September near Halema‘uma‘u Crater. By November 1, more than 1,000 tiny earthquakes were being recorded per day. Scientists conducted another caldera tilt survey during the second week of November and discovered it was swelling at least three times faster than during the previous months. Magma was moving into the summit reservoir at a high rate.
During the afternoon of November 14, earthquakes beneath the caldera suddenly increased about tenfold in both number and intensity. For five hours, the entire Kīlauea summit region shook as seismic tremor signaled magma was forcing its way from the summit reservoir toward the surface.
Eruption begins with a line of lava fountains that narrows to single vent.
An erupting fissure of small lava fountains broke through the south wall of Kīlauea Iki Crater at 8:08 p.m. By 9:30 p.m., the fissure system was 900 m (985 yd) long, and the fountains grew from 15 to 30 m (50 to 100 ft) high. Lava cascaded down the steep forested slopes about 100 m (330 ft) to the bottom of the crater, where it pooled in a growing pond of lava.
In the first 24 hours, activity decreased and then eventually ceased at the outermost fissure vents. By nightfall on November 15, only a single vent on the west side of the fissure remained active. As lava fountains along the fissures stopped, the volume of lava erupted by the single vent increased, and fountain heights rose to 60 m (200 ft) by November 16.
Increased eruption rate forms a cinder cone and deep lava lake.
By early morning on November 17 cinder, spatter, and pumice (tephra) from the growing lava fountain were falling onto the south rim of Kīlauea Iki Crater, the downwind (leeward) side of the vent. The falling fragments began to build a new cinder cone, eventually named Pu‘u Pua‘i (gushing hill). Tephra and lava from the fountain also fed an ever-deepening lava lake within Kīlauea Iki Crater. Over the next five days, lava fountain heights fluctuated between about 200 and 300 m (650 and 980 ft), with a maximum fountain height of 380 m (1,247 ft).
On November 21, the lake level rose above the vent, so the fountain had to blast through more than a meter (yard) of the overlying lava before shooting skyward. At 7:25 p.m. on November 21, without any apparent warning, the fountain decreased from a height of 210 m (690 ft) to a few gas bubbles in less than 40 seconds. The first, and longest, of 17 explosive episodes was over. At the end of the first episode, the lava lake volume was nearly 31 million cubic meters (about 40 million cubic yards) – enough to fill 12,400 Olympic-size swimming pools. As the fountaining ended, lava from the 98-m- (320-ft-) deep lake began draining back into the vent. Drainback stopped when the lava lake reached the level of the vent.
Lava lake depth and fountain heights fluctuate during next 16 episodes.
The next 16 episodes were similar to the first, except for their smaller volumes of erupted lava and shorter durations. Fountaining lava added tephra to the Pu‘u Pua‘i cone and accumulated in the lava lake, which eventually overtopped the vent. As lava covered the vent, the height of the fountain typically fluctuated wildly before stopping altogether. At the end of several episodes, lava began flowing back into the vent even as the fountain continued. During lava lake drainback events, huge slabs of lake crust were pulled down into the vent, sometimes forming a giant counter-clockwise whirlpool over it.
Highlights of the Eruption:
- Large parts of the steep, unstable face of Pu‘u Pua‘i occasionally slid into the vent or lake. Some parts of the cone were rafted a few hundred meters (yards) east across the lake where today they form topographic highs ("islands") above the surface of the cooled lake.
- On December 17, episode 15 produced lava fountains that were approximately 580 m (1,900 ft) high, the highest recorded in Hawaii during the 20th century.
- The greatest volume of spatter and pumice was produced during the 3rd episode. About 900 m (2,950 ft) south of the vent, about 75 cm (30 in) of tephra was added to the 25 cm (10 in) laid down by episodes 1 and 2. Tephra fragments were carried 16 km (10 mi) downwind.
- The elevation of the vent controlled the level of the lava lake. The largest cone slumps occurred after episode 3, causing the vent geometry to change. At the onset of episode 4, the vent was about 12 m (40 ft) higher, so the lake level rose significantly higher during subsequent episodes. The lake reached its maximum depth (126 m, 413 ft) during episode 8 on December 11.
- With every filling and subsequent draining of the lava lake to vent level, a prominent "black ledge" developed around the margin of the lake like a bathtub ring. The ledge grew toward the lake's center as lava was repeatedly plastered on top and to the sides of the ledge.