Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified (sometimes referred to as frozen lava lakes). Not to be confused with crater lakes, lakes of water that form in a volcanic crater or caldera.
Formation
Lava lakes can form in three ways :
- From one or more vents in a crater that erupts enough lava to partially fill the crater; or
- When lava pours into a crater or broad depression and partially fills the crater; or
- Atop a new vent that erupts lava continuously for a period of several weeks or more and slowly builds a crater progressively higher than the surrounding ground.
Behaviors
Lava lakes occur in a variety of volcanic systems, ranging from the basaltic Erta Ale lake in Ethiopia and the basaltic andesite volcano of Villarrica, Chile, to the unique phonolitic lava lake at Mt. Erebus, Antarctica. Lava lakes have been observed to exhibit a range of behaviours. A "constantly circulating, apparently steady-state" lava lake was observed during the 1969-1971 Mauna Ulu eruption of Kīlauea, Hawaiʻi.
By contrast, a lava lake at the 1983-1984 Puʻu ʻŌʻō eruption of Kilauea displayed cyclic behaviour with a period of 5–20 minutes; gas "pierced the surface" of the lake, and the lava rapidly drained back down the conduit before the onset of a new phase of lake activity. The behaviour observed is influenced by the combined effects of pressure within the reservoir, exsolution and decompression of gas bubbles within the conduit and, potentially, exsolution of bubbles within the magma reservoir. Superimposed upon this is the effect of bubbles rising through the liquid, and coalescence of bubbles within the conduit. The interactions of these effects can create either a steady-state recirculating lake, or a lake level that periodically rises and then falls.
Notable examples
Persistent lava lakes are a rare phenomenon. Only a few volcanoes have hosted persistent or near-persistent lava lakes during recent decades :
- Ambrym, Vanuatu
- Mount Erebus, Ross Island, Antarctica
- Erta Ale, Ethiopia
- Kīlauea, Big Island, Hawaiʻi
- Masaya volcano, Nicaragua
- Mount Michael, Saunders Island, South Sandwich Islands
- Mount Nyiragongo, Democratic Republic of the Congo
- Mount Yasur, Vanuatu
The lava lakes at Ambrym volcano disappeared after a large eruption in December 2018.
For many years, Kīlauea had two persistent lava lakes: one in the Halemaʻumaʻu vent cavity within the summit caldera, and another within the Puʻu ʻŌʻō cone located on the east rift zone of the volcano. In May 2018, both of these lava lakes disappeared as a result of increased activity in Kīlauea's east rift zone. The lava lake at Halemaʻumaʻu returned in December 2020, after Kīlauea's first eruption in over two years. The lava lake solidified after the eruption ended in May 2021, but returned again when eruptive activity at Halemaʻumaʻu resumed on September 29, 2021. The lava lake is still active as of September 2022.
Nyiragongo's lava lake has usually been the largest and most voluminous in recent history, reaching 700 meters wide in 1982, although Masaya is believed to have hosted an even larger lava lake at the time of the Spanish conquest, being 1,000 meters wide in 1670. The lava lake at Masaya came back in January 2016.
In addition to the aforementioned persistent lava lakes, a certain number of occurrences of temporary lava lakes (sometimes called lava ponds or lava pools, depending on their size and nature) have also been observed and are listed in the following table.
Lava lake in Seismic “Songs”
Although there are around 1,350 potentially active volcanoes across the globe, only a handful feature lava lakes. One of those lava lakes resides in a crater of Hawaii’s Kīlauea volcano.
Kīlauea famously erupted in 2018, leading to the collapse of its summit. Preceding this eruption, the volcano showcased other, less dramatic eruptions, but there is still much unknown about what happened within the volcanic system leading up to these events.
New research published in Science Advances turned to Kīlauea’s lava lake for answers. The lake gives a direct window into the magma, said Josh Crozier, lead author of the new paper and a researcher now at the U.S. Geological Survey’s (USGS) California Volcano Observatory.
“A lava lake is like opening a manhole in the sewer system: We can see the pressure that’s built up and how fast it is flowing,” Crozier said. “Once something physically disturbs the magma chamber or the lava lake, it sloshes around, and we can measure that with seismometers.”
The researchers carefully examined resonant signals collected by the Hawaiian Volcano Observatory from 2008 to 2018, which allowed them to deduce what was happening inside the volcano without directly probing the hazardous and extreme environment. Crozier and coauthor Leif Karlstrom, an Earth scientist at the University of Oregon, focused on “very long period” (VLP) signals, at frequencies below 5 hertz. These “much gentler and resonant shakings” are produced by other seismic signals made by volcanoes, according to USGS. The authors found that the resonance characteristics encoded in the seismic signals collected around Kīlauea are determined by the shape and properties of the volcano’s magma chamber, like temperature and gas content.
The volcano’s “plumbing system,” which keeps fresh magma coming into the lava lake, produces a seismic resonance somewhat analogous to the musical sound produced by a drum, said Karlstrom. “If you hit a drum, how long does it last before the sound stops? That’s determined by the shape of the drum and what’s inside,” Karlstrom, who is also a musician, said. “In the case of volcanoes, we’re using seismic displacement—not sound” to provide information about the volcano’s inner dynamics and characteristics.
The different kinds of seismic signals can be compared to various instruments in the “song” of information coming from a volcano, said Crozier. “That’s the thing we are still working on to understand,” he said. “We’ve now been given data on it-we can kind of see the score now, instead of just hearing some nice noises.”
Although volcanologists have historically made successful eruption forecasts, such as the warning that went out during the 2018 Kīlauea eruption, there are big errors in current models. Changing signals heralding the buildup of gas or new magma coming in from the depths of the volcano could be considered to be like choruses in the song of the seismic signals coming from the volcano. Crozier : “Some volcanoes are pop songs where there is a predictable structure, and others might be more complicated,” he said. Both Crozier and Karlstrom explicitly said this study is not going to lead to new ways to predict volcanic eruptions overnight, but eventually, it could help scientists make more informed interpretations of the volcano’s seismic signals.
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