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

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Time-lapse thermal image movie of Halemaumau Overlook Vent. March 3-10, 2016. Images courtesy of USGS/HVO

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Time-lapse movie of Halemaumau Crater looking Southwest. March 3-10, 2016. Images courtesy of Hawaii Volcanoes National Park

The ongoing eruption at Kīlauea Volcano’s summit began on March 19, 2008. Since that time, Island of Hawai‘i residents have had to cope with the challenges of increased vog and its effects.

KÄ«lauea Volcano’s summit eruption began on March 19, 2008, and continues today. The lava lake is contained within the Overlook crater, which is set within the larger Halema‘uma‘u Crater. In this February 28, 2016, photo, the lava lake surface was just 30 m (100 ft) below the rim of the Overlook crater. Spattering is visible in the southeast portion of the lake. USGS photo.

On the other hand, the glowing lava lake within the summit vent provides a beautiful sight, drawing hundreds of visitors to Hawai‘i Volcanoes National Park nightly. When the lava lake briefly rose and spilled onto the floor of Halema‘uma‘u Crater in April and May 2015, it showed itself as a vivid reminder of Kīlauea’s dynamic nature.

While noting its 8th anniversary this month, it’s also worth reflecting on what Kīlauea’s summit eruption has taught us. One remarkable aspect of the eruption is the lava lake. There are only a few lava lakes on Earth, and the Halema‘uma‘u lava lake is the second largest—only slightly smaller than that in Nyiragongo Volcano in the Democratic Republic of the Congo.

Kīlauea’s lava lake is a rare opportunity to study the volcano’s dynamic magmatic system. So, what have we learned?

Lava lakes are often called “windows” into a volcano’s deep magmatic system, because they literally are part of a direct pipeline from the deep magma chamber to the surface. What happens in the deep magmatic system—like changes in magma supply rate or internal pressure—should be reflected in the lava lake at the surface. USGS Hawaiian Volcano Observatory (HVO) scientists and their collaborators have closely studied Kīlauea’s summit lava lake, and now have several years of detailed observations to test this idea.

Does the summit lava lake actually provide insights into the unseen magmatic system below? Research is still in progress, but results thus far indicate that the answer is “yes and no.”

If you follow HVO’s daily eruption updates, or view Kīlauea’s summit webcams, you can see that the summit lava lake level changes frequently. And if you follow closely, you probably have noticed that when summit tiltmeters show deflationary tilt, the lava lake drops, while inflationary tilt corresponds to a rising lava lake. Tiltmeters essentially measure pressure within the summit magma chamber, and so, inflationary tilt means higher pressure and deflationary tilt indicates lower pressure.

The close relationship between the summit lava lake level and ground tilt is remarkable, because it demonstrates that the lake behaves like a pressure gauge of the deeper magma chamber—akin to a giant liquid barometer. This is an important example of how the lava lake is, indeed, a window into the state of the deep magma chamber.

Now, let’s look at an example of when this “window” idea appears to break down.

The lava lake surface constantly flows from one side of the lake, where magma rises from depth, to the opposite side of the lake, where it sinks. At first glance, this seems to directly show the process of magma circulating between the deep magma chamber and the lake surface, like an enormous lava lamp. While this may be true most of the time, observations show that the lava lake’s surface flow is often interrupted by spattering and rockfalls, which completely change the speed and direction of the lake surface circulation.

Data show that spattering and rockfalls do not seem to have a deep trigger. Instead, they reflect shallow processes near the lava lake’s surface. These sporadic changes in the lake’s circulation are examples of how the lava lake reflects near-surface processes, and do not always indicate processes in the deep magma system.

Beyond these insights, a remaining question is how long the summit eruption will last. Unfortunately, there is no definitive data we can gather to answer this question.

The best we can do is look at Kīlauea’s recent history. A lava lake was frequently present at Kīlauea’s summit for over a hundred years—from the early 1800s into the early 1900s. This persistence suggests that Kīlauea’s summit lava lakes have the potential to last for decades.

With the East Rift Zone’s Pu‘u ‘Ō‘ō eruption reaching its 33rd anniversary in January 2016, Kīlauea Volcano is remarkable among the world’s volcanoes for having two long-term, concurrent eruptions. While having such an active volcano in our backyard presents both benefits and challenges, Kīlauea will likely remain one of Earth’s most outstanding teachers of volcano science for years to come.