Projects - Volatile Transfer

 

Magma recharge and mixing is not only thought to be important in generating the magma diversity we see on Earth, but also responsible for such different processes such as triggering of volcanic eruptions and enrichment of precious metals. The two historic Quizapu eruptions (Chile)  from 1846-47 and 1932 of similar size (4-5 km3) are an excellent natural laboratory to understand the processes drive explosive-effusive transitions and the transfer of chalcophile elements during mixing. While the plinian 1932 eruption (void of significant mafic magma input) represents the “control magma system” that is almost unaffected by magma recharge, the 1846-47 lava eruption is significantly mingled and mixed with mafic magmas. The silicic end-member in both eruptions were identical (67 wt% SiO2) and were part of the same storage system at depth, thus, allowing such direct comparison and derivation of a causal connection between recharge and volatile transfer that itself is tied to eruptive style and precious metal mobility.


Effusive-Explosive Transitions in Eruption Style

So, why did these two eruptions unfolded in such contrasting ways? The 1846-47 eruption affected the local area by covering 50 km2 with lava, while the 1932 eruption spread ash across large parts of the South American continent.

























A careful investigation of magmatic temperatures recorded by minerals in the magma shows that the major difference between these two eruptions was a drastically different eruptive temperature. The magma of the 1846-47 eruption was significantly reheated by over 130 ˚C from 870 to 1000 ˚C leading to enhanced magma degassing and ultimately diminishing the potential for rapid magma expansion and explosive behavior. In contrast, the 1932 magma did not experience extensive magma reheating, gases were trapped longer in the magma during ascent and an explosive eruption was the result.

The effect of temperature has been often under-appreciated in understanding the transition from effusive to explosive volcanism. In the case of 1846-47 Quizapu eruption the heat was provided by hot recharge magma that mixed and mingled with the dacite magma. The 1932 magma shows almost no signs of mafic recharge.

This effect of magma recharge and ensuing reheating is probably also important for other less explosive silicic eruptions (e.g., Unzen, Montserrat, Pinatubo, Nisyros) that show extensive magma mingling with recharge magma. In some cases, hot pre-eruptive magmatic temperatures have been documented, but they have not been connected to the volcano’s eruptive behavior.


What happens as two magma physicochemically as two magmas mix?


Relevant publication:

Ruprecht P., Bachmann O. (2010). Pre-eruptive reheating during magma mixing at Quizapu volcano and the implications for the explosiveness of silicic arc volcanoes. Geology 38: 919-922, doi: 10.1130/G31110.1.

Magma RECHARGE - a FACILITATOR FOR EFFUSIVE ERUPTIONS AND SULFUR MOBILITY?

Figure


Reheating in the dacite is accomplished as the hot recharge magma exchanges sensitive heat during mixing and mingling. Additional heat is provided from the recharge magma through latent heat production as the magma crystallizes significantly (a). Diffusive heat transfer from the hot  recharge magma occurs on short length scale (b) as the magma mingling produces vesiculated crystallized mafic enclaves distributed only centimeters apart.

Photos: Quizapu Crater in the evening light. The area is covered by the 1932 dacitic plinian eruption. The topography still shows the lava flows from an earlier activity at Quizapu. In 1846-47 4-5 km3 of similar magma to 1932 erupted as effusive lavas. How can very similar magmas erupt so different? Find the answer here.

Quizapu crater at sunsetResearch.htmlshapeimage_2_link_0