Images

A burping driblet spire (hornito) in 'Alae Crater on May 20, 1970. In volcanology, a hornito is a rootless vent developed on, and fed by, a lava flow or lake. There was no recognized deeper vent in 'Alae Crater, so this feature is probably a real hornito.

Today ‘Ālo‘i is unrecognizable except by keen observers.

The only surviving segment of the fissure system active on the first day of the eruption. View looks west and shows the fissure segments, stepping right, and spatter rampart along right (uphill) side of the segments. No spatter rampart formed on the downhill (left) side of the segments, because falling spatter was carried away by lava flows.

 HVO scientist measures the episode 12 lava fountain height at Mauna Ulu from Puʻu Huluhulu on Dec 30, 1969. The Mauna Ulu eruption marks its 51^st anniversary on May 24, 1969.

Tilted slabs of welded spatter blanketed by pumice and spatter erupted on October 20 and, mainly December 30, 1969. Note the contrast between the chaotic terrain in the foreground and the undisturbed bedding in tephra in background. The chaotic area formed as moving lava upended the tephra beds. Photo taken in March 1970.

Viewing platform for visitors on rim of Mauna Ulu crater. March 22, 1973. This platform, established in 1972, was open to the public until late on the night of November 4, 1973. Then rising lava level prompted closure, and lava engulfed the platform early the next morning.

Fallout on flank of Pu'u Huluhulu from inclined fountain of October 20, 1969. The high vertical fountain was briefly diverted toward Pu'u Huluhulu when a blockage developed at the vent. Observers at the viewing platform (on the left-most peak on the skyline) scrambled to escape, but after several minutes the fountain righted itself.

Lava fountain of October 20, 1969 with viewing platform on top of Pu'u Huluhulu. The viewing platform has a stone wall facing the fountain; it can be reached by a national park trail. The platform was occupied by HVO geologists during fountaining episodes, from which the height of the fountains was measured and photos and movies taken.

Dome fountain of episode 10, October 10-13, 1969. Photo taken on October 11. This dome fountain is about 20 m (65 ft) high. Symmetrical dome fountains such as this are rare.

The graben that opened on August 4, 1969, is in lower left, near the spillover.

Tallest fountain of the eruption, 540 m (1770 ft) on September 6, 1969. Photo from '?lo'i Crater. Lava flows during this fountaining episode filled 'Alae Crater.

Photo taken on September 1, 1969. The mound was broken up and later buried by lava flows.

Same area as that shown in previous photo but a day later, showing how rapidly the vent configuration can change during active spattering. August 16, 1969.

Small spattering fountain about 8 m (25 ft) high at Mauna Ulu on August 15, 1969. Episodes of high fountains occurred on August 5 and 22, but low-level activity such as this, as well as that shown in the previous three images, was almost constant between the episodes of high fountaining in 1969.

Lava falls higher than American Falls at Niagara begin to fill 'Alae Crater on August 5, 1969, following the catastrophic draining on August 4. Renewed fountaining at Mauna Ulu sent lava shown in the photo into 'Alae, starting to refill the crater. Photo taken from same location as the preceding image.

Graben that drained some of the lava out of 'Alae on August 4, 1969. Photo taken on September 24, 1969. The graben, more than 10 m (30 ft) wide and locally more than 70 m (230 ft) deep, extended 800 m (2,600 ft) east-northeast from 'Alae. and a trough reached 700 m (2,300 ft) farther. It was an older structure but was reactivated during the draining.

East end of 'Alae Crater after catastrophic draining on August 4, 1969. The entire crater was nearly full of lava erupted in February 1969 and later by Mauna Ulu, most recently on August 3.

West end of 'Alae Crater, showing exhumed mezzanine, after catastrophic draining on August 4, 1969.

Close-up of right side of lava pool shown in previous image a few seconds later, showing early stage of gas-piston draining. Pond level has already dropped several meters. During the next 30 seconds the pond level dropped 25-30 m (80-100 ft) as gas escaped from the pond, creating a void immediately filled by the draining lava.

Pool of lava filling a basin 150 m (500 m) wide at the summit of Mauna Ulu on July 29, 1969. This image and the next two illustrate a process called gas pistoning. The pool is fed by lava rising 50 m (160 ft) in 15 minutes up a fissure 3-7 m (10-25 ft) wide. Bubbling is just starting above the fissure, leading to draining shown in the next image.

Same view as in previous image, but about 20 seconds later. Now lava is now falling into the fissure, destroying sheets of crust in the process. When the draining was over, lava level had dropped about 50 m (160 ft). Once draining was complete, lava level again began to slowly rise as it was pushed upward by expanding gas bubbles.