What's been driving Hawaii's lava fountains?

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In most cases, hotspot-driven volcanism is relatively sedate, with lava flowing down mountainsides slowly enough that people can walk out of its way. But in a number of locations—Mount Etna, Hawaii, Iceland—lava gets expelled in dramatic fountains that can reach several hundred meters in height. Right now, we’re not sure what powers them.

在大多数情况下，由热点驱动的火山活动相对平稳，熔岩沿山坡流下的速度足够慢，人们可以步行避开。但在一些地方——如埃特纳火山、夏威夷和冰岛——熔岩会以壮观的喷泉形式喷发，高度可达数百米。目前，我们尚不确定是什么力量驱动了这些喷泉。

However, thanks to a recent set of eruptions at the Kilauea volcano, we have some of the best documentation yet of erupting lava fountains. In a recent edition of Science, researchers from the US Geological Survey describe what we’ve seen and compare it with what we might expect based on our best ideas about what powers these fountains of molten rock.

然而，多亏了基拉韦厄火山最近的一系列喷发，我们获得了迄今为止关于熔岩喷发最详尽的记录之一。在最近一期的《科学》杂志中，美国地质调查局的研究人员描述了我们所观察到的现象，并将其与我们基于现有理论对熔岩喷泉驱动机制的预期进行了对比。

Years of fountains: With three active volcanic regions that engage in fountaining, there has been a steady flow of dramatic videos of red-hot molten rock spouting from the Earth. But Kilauea has had only three fountaining episodes since 1823, even though it’s the youngest and most active volcano in Hawaii. That activity has led to intensive study, and we have a good idea of the volcano’s structure.

多年的喷发：由于有三个活跃的火山区会产生喷泉现象，源源不断的视频记录下了炽热的熔岩从地球喷涌而出的壮观景象。但自1823年以来，基拉韦厄火山仅发生过三次喷泉事件，尽管它是夏威夷最年轻、最活跃的火山。这种活动引发了深入研究，使我们对该火山的结构有了很好的了解。

Previous work has identified a couple of lava residues within a few kilometers of the surface, and the volcano had 35 separate data-gathering stations set up on Kilauea, including “seismic, infrasound, geodetic, gas, and visual and thermal cameras.” Following a major eruption in 2018 that partly drained one of the underground lava reservoirs, there were indications that it was being steadily refilled.

先前的研究在距离地表几公里的范围内确定了几处熔岩残留物，并且在基拉韦厄火山上设置了35个独立的数据采集站，包括“地震、次声、大地测量、气体以及视觉和热成像摄像机”。在2018年一次大规模喷发导致其中一个地下熔岩库部分排空后，有迹象表明它正在稳步回填。

Starting in 2019, however, the refill accelerated, and the local peak inflated at a rate of more than 22 cm a year. Then, in 2023, that doubled to 57 cm a year, and spread to a nearby caldera. In 2024, a large series of earthquakes accompanied the opening of a vent, and a 900-meter-long fissure opened, sending fountains as high as 160 meters into the sky over the course of 13 hours.

然而，从2019年开始，回填速度加快，当地山峰以每年超过22厘米的速度隆起。随后，在2023年，这一速度翻倍至每年57厘米，并蔓延至附近的火山口。2024年，一系列大规模地震伴随着喷口的开启，一条900米长的裂缝裂开，在13小时内将高达160米的熔岩喷泉送入天空。

Less than a day after that subsided, a second eruption followed. As of last month, 52 additional fountain eruptions had occurred, the most violent of which spewed lava over 400 meters into the air. What have we learned from all of this? Perhaps the most significant finding was that we could predict when a fountaining eruption was likely to happen.

在喷发平息不到一天后，第二次喷发随之而来。截至上个月，又发生了52次喷泉喷发，其中最猛烈的一次将熔岩喷射到400多米的高空。我们从这一切中学到了什么？也许最重要的发现是，我们能够预测喷泉喷发何时可能发生。

Each eruption caused rapid deflation of the summit of Kilauea and was followed by the relatively slow refilling of the Halemaʻumaʻu magma reservoir. The USGS recognized that consecutive eruptions occurred when the summit tilt reached similar levels. While the precise tilt that was associated with eruptions tended downward over time, the difference between consecutive eruptions was relatively small.

每次喷发都会导致基拉韦厄山顶迅速塌陷，随后是哈雷茂茂岩浆库相对缓慢的回填。美国地质调查局发现，当山顶倾斜度达到相似水平时，连续的喷发就会发生。虽然与喷发相关的精确倾斜度随时间呈下降趋势，但连续喷发之间的差异相对较小。

This pattern ultimately helped the organization issue alerts when eruptions were likely to occur, which was especially useful because there were no clear seismic signals immediately before fountains restarted. What’s driving this? What have the eruptions told us about the mechanism that drives fountain formation?

这种模式最终帮助该机构在喷发可能发生时发布警报，这一点特别有用，因为在喷泉重新开始前并没有明显的地震信号。是什么驱动了这一切？这些喷发告诉了我们关于驱动喷泉形成的机制是什么？

One leading idea is that pressure within a magma reservoir keeps water mixed with other materials until it reaches a shallow enough depth to exit as steam. That fragments the magma, which allows it to ascend more rapidly, which allows more steam to escape, and so on until there’s a jet of material near the surface.

一个主要的观点是，岩浆库内的压力使水与其他物质混合，直到它到达足够浅的深度，以蒸汽的形式排出。这会使岩浆破碎，从而使其上升得更快，进而让更多的蒸汽逸出，如此循环，直到在地表附近形成物质喷流。

The alternative posits that things are driven by the release of carbon dioxide from the magma, which forms a magma/gas “foam” at the roof of the magma chamber. Once this reaches a critical point, the gas escapes, driving magma with it until the supply in the magma chamber is exhausted. The new data doesn’t provide a clear picture.

另一种观点认为，这是由岩浆中释放的二氧化碳驱动的，二氧化碳在岩浆房顶部形成岩浆/气体“泡沫”。一旦达到临界点，气体就会逸出，带动岩浆一起喷出，直到岩浆房内的供应耗尽。新数据并没有提供清晰的结论。

It clearly doesn’t favor the formation of a carbon dioxide foam, because the levels of the gas remained low throughout the eruption cycle. Sulfur dioxide levels rose during eruptions and dropped afterward, but remained high throughout the entire period. Levels of this chemical are associated with gases escaping from magma, so this implies that more of it goes on during eruptions, but it also occurs continuously between them.

它显然不支持二氧化碳泡沫形成的理论，因为在整个喷发周期中，该气体的水平一直很低。二氧化硫水平在喷发期间上升，之后下降，但在整个期间一直保持在高位。这种化学物质的水平与从岩浆中逸出的气体有关，这意味着喷发期间逸出量更多，但在喷发间隙也持续存在。

So the evidence leans toward the steam-driven eruption model, but it’s unclear why a process that is occurring throughout the cycle suddenly triggers fountains when it rises a bit. The other bit of information from the chemistry of the eruption is from magnesium oxide, which provides an indication of the temperature of the magma.

因此，证据倾向于蒸汽驱动的喷发模型，但不清楚为什么一个在整个周期中都在进行的进程，在稍微增强时会突然触发喷泉。来自喷发化学成分的另一个信息来自氧化镁，它提供了岩浆温度的指示。

It fluctuated throughout the eruption cycle, consistent with a cycle in which eruptions deplete a reservoir, which is then refilled with hot material. In contrast, other oxides rose over time, suggesting that the newly arriving material has a distinct chemical composition. Despite the wealth of nearby sensors, the researchers acknowledged it would be nice to have more data.

它在整个喷发周期中波动，这与喷发消耗岩浆库、随后又被热物质回填的循环相一致。相比之下，其他氧化物随时间上升，表明新到达的物质具有独特的化学成分。尽管附近有大量的传感器，研究人员承认，如果能有更多的数据会更好。

Sampling of gas levels is typically done at infrared wavelengths and, as you can probably imagine, there was a lot going on in the infrared during a fountaining eruption. And, because of the height of some of the fountaining, it wasn’t necessarily safe to install more monitoring hardware. One camera notably sacrificed itself in order to bring us images of red-hot, semi-molten rock falling from the sky.

气体水平的采样通常在红外波段进行，正如你所能想象的那样，在喷泉喷发期间，红外波段存在大量干扰。而且，由于一些喷泉的高度，安装更多的监测硬件并不一定安全。值得注意的是，有一台摄像机为了给我们带来炽热的半熔融岩石从天而降的图像而“牺牲”了自己。

While Kilauea has proven itself as a spectacular lab for studying volcanic activity, it hasn’t yet proven ready to give up all its secrets.