Mount Tarawera's explosive 1886 eruption may have been spurred by “nanolite” crystals. Credit: Rod Hil Getty Images
塔拉威拉山（Mount Tarawera）1886年的爆发性喷发可能是由“纳诺石”晶体引起的。图片来源：Rod Hil Getty Images
Volcanoes that are thought to be mild-mannered, releasing steady lava flows, can sometimes erupt explosively without warning—as New Zealand's Mount Tarawera did in June 1886, causing widespread damage and death. Geologists have long wondered why volcanoes make this sudden and dangerous transition, says earth scientist Danilo Di Genova of the University of Bayreuth in Germany.
火山被认为是温和的，释放出稳定的熔岩流，有时会在没有预警的情况下爆发性爆发-就像新西兰的塔拉威拉山（Mount Tarawera）在1886年6月所做的那样，造成广泛的破坏和死亡。德国拜罗伊特大学的地球科学家达尼洛·迪格诺瓦（Danilo Di Genova）说，地质学家一直想知道为什么火山会发生这种突然而危险的转变。
Di Genova and his colleagues propose in Science Advances that such a catastrophic switch may begin with crystal grains called nanolites, which can form in rising magma and are only about 1/100th the size of an average bacterium. The researchers say these grains make magma more viscous, preventing volcanic gases from escaping the molten rock. This builds up pressure, setting the stage for a violent explosion.
Di Genova和他的同事在《科学进展》中提出，这种灾难性的转变可能始于被称为纳米晶的晶粒，这种晶粒可以在上升的岩浆中形成，其大小仅为平均细菌大小的1/100左右。研究人员说，这些颗粒使岩浆更加黏稠，防止火山气体逸出熔融岩石。这会增加压力，为猛烈爆炸做好准备。
The team then examined how nanolites form in a comparatively runny type of magma that becomes basalt when it cools. Such low-viscosity magma usually allows gases to escape easily, leading to smooth lava flows. The researchers produced nanolites in the laboratory by melting basalt and then cooling it rapidly. The cooling process is critical: during eruptions, magma loses heat as it rises toward the top of a vent. The study found nanolites will form only if the heat loss rate is just right, Di Genova explains.
利用电子显微镜和光谱成像工具，科学家们在活火山的火山灰中发现了纳米岩，包括意大利的埃特纳火山和印度尼西亚的坦波拉。
“Magma is a multicomponent system, mainly made by silicon and oxygen,” Di Genova says. “It has other elements such as aluminum, calcium and iron, the last of which seems to be the most important element in forming nanolites.” Most of the nanolites are iron oxide crystals with traces of aluminum, he adds. And because iron is found in all magmas, such crystals can form in various magma types.
然后，研究小组研究了纳米流岩如何在一种相对流淌的岩浆中形成，这种岩浆在冷却时变成玄武岩。这种低粘度的岩浆通常使气体容易逸出，从而导致熔岩流顺畅。研究人员在实验室中通过熔化玄武岩然后将其快速冷却来生产纳米晶。冷却过程至关重要：在喷发期间，岩浆会朝着通风口顶部上升而散失热量。Di Genova解释说，该研究发现，仅当热量损失率合适时，纳米晶才会形成。
Next the researchers created an artificial magma to show that nanolites boost viscosity. They used silicon oil (which is as viscous at room temperature as basalt magma is during an eruption), adding glass spheres to mimic nanolites in shape and size. The team found that even at relatively low concentrations nanoparticles tend to clump together, disrupting the free flow of the liquid. In a real volcano, this sudden increase in the magma's viscosity would trap bubbles of escaping gas. Eventually enough pressure would build to push out blobs of magma all at once rather than in a steady stream—resulting in an explosion.
Di Genova说：“岩浆是一种多组分系统，主要由硅和氧制成。” “它还含有铝，钙和铁等其他元素，最后一种似乎是形成纳米晶的最重要元素。” 他补充说，大多数纳米石是具有微量铝的氧化铁晶体。而且由于在所有岩浆中都发现了铁，因此可以以各种岩浆类型形成这种晶体。
“This is an exciting study that addresses a question we have had for a long time,” says Columbia University geologist Einat Lev, who was not involved in the new research. “It will be important and challenging to figure out how to incorporate this information in future volcanic models.”
接下来，研究人员创建了一个人造岩浆，以表明纳米晶可以提高粘度。他们使用了硅油（在室温下，其粘度与喷发时玄武岩岩浆一样黏稠），并添加了玻璃球以模仿形状和大小的纳米晶。研究小组发现，即使在相对较低的浓度下，纳米颗粒也趋于聚集在一起，从而破坏了液体的自由流动。在真正的火山中，岩浆黏度的这种突然增加会捕获逸出气体的气泡。最终，将形成足够大的压力，以一次全部而不是源源不断地喷出岩浆，从而导致爆炸。
Using electron microscopy and spectroscopic imaging tools, the scientists found nanolites in the ashes of active volcanoes, including Mount Etna in Italy and Tambora in Indonesia.
哥伦比亚大学的地质学家埃纳特·列夫（Einat Lev）说：“这是一项令人兴奋的研究，它解决了我们长期以来遇到的一个问题。” “弄清楚如何将这些信息纳入未来的火山模型将是重要且具有挑战性的。”