Failure to Launch: Andes, Lava Coulée, and Chao Baby!

       Geologists from

Heidelberg University have discovered deposits of magma in the Andes sufficient to have set off a super-eruption but which, in fact, did not. 

     Researchers discovered that magma volumes of supervolcanic proportions have been continuously accumulating in the Altiplano-Puna region of the Andes since the last super-eruption nearly 2.9 million years ago. 

     These magmas, however, did not reach the surface to trigger a catastrophic eruption but instead slowly cooled at depth and hardened into plutonic rock, similar to the area we discussed in Russia two weeks ago. The results of the research were published in the journal Geology.

       
      Unlike the pluton they describe, the Chao volcano in northern Chile with a lava coulée (or flow) approximately 14.5 km long in the center of the image above flowed at the surface. The composition of the lava matches that of deposits of adjacent supervolcanic calderas. Chao erupted about 75,000 years ago, but zircon crystals in the lava were already forming in a subterranean magma reservoir for nearly three million years.

     "A supervolcanic eruption spews out more than 1,000 cubic kilometers of magma, which accumulated over time in reservoirs close the earth's surface," explains Dr. Axel Schmitt.

       "In turn, these reservoirs are fed from deeper layers in the earth's crust and the underlying mantle. During an eruption, the overlying rock layers collapse into the empty magma chamber and form depressions, known as calderas, of up to 100 kilometers in diameter." Schmitt indicates that there have been at least seven super-eruptions in the Altiplano-Puna region within the last ten million years, the most recent one about 2.9 million years ago. We don't understand why no further major eruptions have occurred since then and whether the region can now be considered inactive for such events.

      Using samples from five small lava domes in northern Chile and southeast Bolivia, the researchers investigated the most recent eruptions whose chemical composition matches the supervolcanic magmas from the region. They determined the age of very small zircon crystals from these lava flows with the aid of a high-spatial-resolution mass spectrometer. 

      "The mineral zircon forms almost exclusively in magmas, so its age reveals when those magmas were present under the volcano," explains Schmitt. "The astonishing result was that the ages of the zircons measured from all five of the smaller volcanoes extended continuously from the time of the eruption 75,000 years ago back to the last supervolcanic eruption."

     Dr. Schmitt reports that model calculations demonstrated that zircon formation is only possible over such long durations if the inflow of magma amounted to approximately one cubic kilometer over 1,000 years, which is unusually high for a relatively small volcano. The volcanologist explains that the lack of a major volcanic eruption does not necessarily indicate that magmatic activity has come to a complete halt. Perhaps the rise in magma from deeper regions merely slowed during the last 2.9 million years, forming a pluton.

      "However, our results also show that a relatively small increase in the long-term magma recharge from about one to five cubic kilometers in 1,000 years would recreate conditions favoring a catastrophic supervolcanic eruption. A new super-eruption in the Altiplano-Puna region would be possible, but only after a long lead time," said Dr.Schmitt.

Have you ever seen anything so (lava) coulée?
Steph