Time-lapse movie of Halemaumau Overlook Vent. The electronic tilt graph shows the radial tilt at Uwekahuna (UWE), on the northwest rim of KÄ«lauea’s caldera, and PuÊ»u ʻŌʻō (POC), on the north flank of PuÊ»u ʻŌʻō cone, as recorded by continuously operating electronic tiltmeters. Positive changes often indicate inflation of the magma storage areas beneath the caldera, but may also result from heavy rainfall or, occasionally, instrumental malfunctions. The Y-axis is in microradians, an angular measure in parts per million; for example, one microradian represents the tilt of a 1-km-long bar, one end of which is lifted up or down 1 mm. April 23-30, 2015. Images courtesy of USGS/HVO

Time-lapse thermal image movie of Halemaumau Overlook Vent. April 23-30, 2015. Images courtesy of USGS/HVO

Time-lapse movie of Halemaʻumaʻu Overlook Vent from Hawaiian Volcano Observatory. April 23-30, 2015. Images courtesy of USGS/HVO

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

An early morning view of the lava lake with a recent overflow onto the floor of Halemaʻumaʻu Crater. Photo taken Thursday, April 29, 2015 courtesy of USGS/HVO

Over the past week, lava has risen within the Halema‘uma‘u Overlook crater (active vent at the summit of Kīlauea) and overflowed onto the floor of the larger Halema‘uma‘u Crater. As a result, visitation to Hawai‘i Volcanoes National Park has skyrocketed. This is understandable because it’s the first time that a lake of lava within Halema‘uma‘u Crater has been visible from Park visitor overlooks since 1974.

The Overlook crater opened on March 19, 2008, but until this week, only the gas plume and nighttime glow from the vent had been visible. Over the years, the vent opening enlarged as parts of its rim spalled off and dropped dramatically into the lava lake. Today, the opening is about 160 m (175 yds) wide and about 220 m (240 yds) long, and the lava lake within it slowly circulates—ascending in the north and descending in the south.

This is the 16th lava lake hosted in Halema‘uma‘u Crater since the explosions of May 1924, which doubled the crater’s width and increased its depth to about 410 m (450 yds).

From 1924 to 1934, seven lava lakes occurred in Halema‘uma‘u, each lasting from 2 to 33 days. After 1934, Kīlauea Volcano was completely inactive until June 27, 1952, when an active lava lake reoccupied Halema‘uma‘u for 136 days. Four more short-lived lava lakes popped up in the crater in 1954 and 1961. Accumulation of lava from these 11 lakes decreased the depth of Halema‘uma‘u Crater to 170 m (186 yds).

In early November 1967, another lava lake was created by an eruption that occurred in phases over a period of 251 days. By the time the eruption ended on July 13, 1968, Halemaʻumaʻu Crater had been filled with another 100 m (110 yds) of lava.

The 1967–1968 eruption produced perched lava lakes or ponds. These are bodies of circulating lava that build their own rims, much like an above-ground swimming pool. The 1967–1968 eruptive phases typically started with lava erupting from, and covering most of, the Halema‘uma‘u Crater floor before being confined within its perched boundaries. The rest of the eruptive phase would consist of stationary and migrating spattering sources, or low lava fountains, within the perched circulating lava lake.

Not long after the 1967–1968 summit eruption ended, activity picked up in Kīlauea’s upper East Rift Zone, where, in 1969, the Mauna Ulu eruption began. Twenty-nine months later, Mauna Ulu activity waned and Kīlauea’s summit started to inflate rapidly. On August 14, 1971, a brief fissure eruption occurred in the east summit caldera. This was followed in September by a 5-day eruption in the Southwest Rift Zone and within Halema‘uma‘u Crater, where lava fountains filled a broad ring along the outer edges of the crater before the summit activity ceased.

This textbook example of a perched lava lake that formed within the Pu‘u ‘Ō‘ō crater in May 2011 shows what could happen with Kīlauea’s current summit lava lake if overflows of the Overlook crater vent continue. Lava overflowing the vent rim could build a levee around the lake, increasing the height of the vent rim and resulting in a perched lava lake within Halema‘uma‘u Crater. USGS photo.

But changes within Halema‘uma‘u Crater were not only due to lava filling. By the end of the September 1971 eruption, the central part of the floor, still covered with 1968 lava, had dropped 45 m (49 yds), leaving a 150-m- (165-yd-) wide bench of lava about halfway up the crater walls. The bench is now narrower, but can still be seen about halfway up the walls of Halema‘uma‘u Crater.

In February 1972, eruptive activity resumed at Mauna Ulu in Kīlauea’s upper East Rift Zone and continued until late July 1974. This was followed by three brief eruptions at the summit and upper Southwest Rift Zone of Kīlauea. The second of these eruptions included a fissure that crossed the floor of Halema‘uma‘u Crater on September 19, 1974. But unlike the September 1971 eruption, the September 1974 eruption remained within Kīlauea Caldera.

The 1974 fissure erupted for less than half a day, but lava covered the Halema‘uma‘u Crater floor—except for the tops of three high spatter cones formed in the 1967–1968 eruption—before the lava level dropped about 7 m (8 yds). The current floor of Halema‘uma‘u Crater is what remains of the September 1974 eruption.

Today’s Overlook crater lava lake (2008 to present) in the floor of Halema‘uma‘u Crater has already outlasted all other Halema‘uma‘u lava lakes since 1924. Will it continue to build a perched lava lake on the Halema‘uma‘u Crater floor? Or will the lava lake collapse back into the crater in response to another rift zone breakout? Whatever happens, USGS Hawaiian Volcano Observatory scientists will be closely watching and documenting the activity.

Time-lapse movie of Halemaumau Overlook Vent from the West Rim of Halemaumau Crater. April 27-30, 2015. Images courtesy of USGS/HVO