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Pondering out of doors the caldera: Working out basaltic eruptions at Yellowstone

Pondering out of doors the caldera: Working out basaltic eruptions at Yellowstone
April 22, 2025



Yellowstone Caldera Chronicles is a weekly column written by way of scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Cole Messa and Ken Sims, from the College of Wyoming, and Mark Stelten, geologist with the U.S. Geological Survey and deputy scientist-in-charge of the Yellowstone Volcano Observatory.

The Basalts of Heat River and Shotgun Valley, which erupted about 1.17 million years in the past after the formation of Henrys Fork Caldera in southeast Idaho.  Photograph by way of Brandi Lawler, College of Wyoming, August 8, 2018.

Virtual elevation style of Yellowstone Nationwide Park and neighborhood, appearing the site of the calderas shaped all the way through every of Yellowstone’s 3 most up-to-date volcanic cycles. The youngest caldera-forming eruption produced Yellowstone Caldera (inexperienced line), positioned inside Yellowstone Nationwide Park. Henrys Fork Caldera (blue line), used to be shaped because of Yellowstone’s 2d caldera-forming eruption, roughly 1.3 million years in the past, and has since been crammed in with basaltic lava flows that purpose the flat, low-relief topography in that area. Determine changed from Christiansen et al. (2007).

The Yellowstone Plateau Volcanic Box has produced 3 caldera-forming eruptions during the last 2.1 million years, together with the Huckleberry Ridge Tuff (2.1 million years in the past), the Mesa Falls Tuff (1.3 million years in the past), and the Lava Creek Tuff that produced Yellowstone caldera 631,000 years in the past. Between those huge eruptions, a large number of lava flows and domes erupted inside the calderas produced by way of those huge eruptions. Even if maximum eruptions at Yellowstone have a tendency to be rhyolite in composition—prime in silica and really viscous, which is why eruptions will also be very explosive and likewise produce thick lava flows—those magmas constitute the top product of a big magmatic machine that extends from ~4 km intensity to the bottom of the crust (~40 km). Actually, rhyolite is handiest found in important amounts between roughly 4 km and 15 km intensity in crust, while the remainder of the magmatic machine is most probably ruled by way of basalt, which comes from deeper within the Earth, is decrease in silica content material, and is a lot more fluid.

Map of Yellowstone caldera appearing the distribution of rhyolites erupted after the formation of Yellowstone caldera and basalts erupted out of doors the caldera.

Geologists have lengthy recognized that enormous, shallow rhyolite magma our bodies like that at Yellowstone want a big provide of warmth to stay stay lively and now not freeze forged. This warmth supply is most definitely associated with the delivery of scorching, basaltic magmas from deep within the crust to shallower parts of the crust the place rhyolite is living. Moreover, an inflow of warmth from deeply sourced basalts is also required to “high” the rhyolite machine for an eruption. In different phrases, the inflow of warmth into the shallow crust may cause the share of liquid magma within the magmatic machine to extend, most likely resulting in an eruption.To check those concepts and higher perceive the function that the deeper, basaltic a part of the magmatic machine performs in priming eruptions within the shallow, rhyolitic phase, a analysis staff representing a collaboration between the College of Wyoming’s Top-Precision Isotope Laboratory (WILD) and the USGS Volcano Science Heart just lately measured eruption ages the use of the argon relationship methodology on suite of samples accrued from all through the Henrys Fork Caldera area, positioned simply west of provide day Yellowstone caldera close to town of Island Park, Idaho. Henrys Fork Caldera is house to a lot of Yellowstone’s basaltic process and has long past most commonly unresearched since mapping efforts by way of the past due Dr. Robert L. Christiansen have been finished in 2001. The brand new eruption ages, coupled with box mapping efforts, published that Henrys Fork Caldera is house to more than one episodes of basaltic lava float process over the last 1.3 million years. Importantly, every of those episodes coincides with a length of recognized rhyolite eruptive process within the Yellowstone area. This alignment of eruption timing led the researchers to signify that sessions of volcanic unrest at Yellowstone are characterised by way of an build up in process within the decrease, basaltic portion of the magmatic machine that gives the warmth vital to spur the shallow, rhyolitic portion of the magmatic machine into rising and/or erupting. Those sessions of higher process within the decrease portion of the magmatic machine are manifested at the floor as sessions the place a large number of basaltic magmas erupt out of doors the caldera, whilst rhyolites, which can be much less dense, “block” the basalt from emerging the place a rhyolite magma chamber is provide—specifically within the space of Yellowstone caldera—however would possibly erupt themselves. This explains why Yellowstone caldera is characterised by way of a large number of episodes of rhyolite lava float process that correlate in time with basaltic process out of doors the caldera. Every other putting conclusion from the brand new analysis is the identity of a basalt eruption this is simply 35,000 years previous positioned within the Henrys Fork Caldera area. Up to now, it used to be concept that the youngest eruption within the area used to be the rhyolite lava of the Pitchstone Plateau about 70,000 years in the past, whilst the youngest recognized basalt float used to be 120,000 years previous. The brand new outcome implies that this 35,000 yr previous basalt is now the youngest Yellowstone eruption recognized. The more youthful age signifies that basaltic process stays conceivable west of Yellowstone Nationwide Park, and that the deeper, basaltic portion of Yellowstone magmatic machine has been lively for the reason that remaining recognized eruption of rhyolite at Yellowstone. The brand new analysis used to be printed within the magazine Geology: “New 40Ar/39Ar Eruption Ages Divulge an Vital Temporal Dating Between Mafic and Silicic Volcanism within the Yellowstone Plateau Volcanic Box.” 

The Pinehaven Basalt, which erupted in Henrys Fork Caldera, southeast Idaho, about 35,000 years in the past.  Photograph by way of Brandi Lawler, College of Wyoming, August 6, 2018.

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