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Evidence in the Cassia Hills of Idaho reveals 12 catastrophic eruptions

And other newly released GSA Bulletin articles

Geological Society of America


IMAGE: Figure 1 from Knott et al. is a map of the Cassia Hills in southern Idaho (C in inset) showing main canyons and locations mentioned in the text. view more

Credit: GSA Bulletin and Thomas R. Knott et al.

Boulder, Colo., USA - Ancient super-eruptions west of Yellowstone, USA, were investigated by an international initiative to examine the frequency of massive volcanic events. Yellowstone famously erupted cataclysmically in recent times, but these were just the latest of a longer succession of huge explosive eruptions that burned a track from Oregon eastward toward Yellowstone during the past 16 million years.

The Cassia Hills of southern Idaho preserve evidence of twelve catastrophic large-scale explosive eruptions, which left widespread glassy deposits fused to the landscape. Each deposit preserves subtly distinctive magnetic, mineralogical, and chemical characteristics that allow them to be traced great distances.

Painstaking work by Thomas R. Knott and colleagues has revealed records of previously undiscovered large-scale eruptions, which caused Earth's crust in the area to subside by more than three kilometers, leaving a deep volcanic basin along the Snake River Plain. These older volcanic eruptions were hotter and probably more frequent than the Yellowstone eruptions.


Mid-Miocene record of large-scale Snake River-type explosive volcanism and associated subsidence on the Yellowstone hotspot track: The Cassia Formation of Idaho, USA
T.R. Knott et al., Department of Geology, University of Leicester, LE1 7RH, UK. This article is OPEN ACCESS online at

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Other recently published GSA BULLETIN articles (see below) cover such topics as

    1. Ghost glaciers;
    2. Holocene climate change in California; and
    3. How garnets mark an earlier collision for the southern Rocky Mountains.

Glacial history and landscape evolution of southern Cumberland Peninsula, Baffin Island, Canada, constrained by cosmogenic 10Be and 26Al
L.B. Corbett et al., Department of Geology and School of Natural Resources, University of Vermont, Burlington, Vermont 05405, USA. This article is online at

Most of Earth's glaciers and ice sheets are erosive, leaving behind ample evidence of their presence on the landscape. But in isolated areas at high latitude, glacial ice can be non-erosive if the basal temperature remains cold enough. Here, we investigate non-erosive glaciers that used to exist on Baffin Island, Canada. So-called "ghost glaciers" leave no physical traces on the landscape, so we resort to chemical evidence to study them. Non-erosive glacial ice has preserved subglacial landscapes for millions of years on Baffin Island, allowing ancient land surfaces to persist over many glacial-interglacial cycles. These ancient surfaces may hold valuable information about high-latitude climate changes over long time durations.

Climate-change versus landslide origin of fill terraces in a rapidly eroding bedrock landscape: San Gabriel River, California
D. Scherler et al., Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, California 91125, USA. This article is online at

In the North Fork of the San Gabriel River, an arid bedrock landscape in the San Gabriel Mountains, California, a series of prominent fill terraces have previously been interpreted as a typical example of how landscapes respond to climate change. Dirk Scherler and colleagues suggest instead that the terraces are a consequence of the sudden supply of unconsolidated material to upstream reaches by one of the largest known landslides in the San Gabriel Mountains. New 10Be-derived surface exposure ages from the landslide deposits, previously assumed to be early to middle Pleistocene in age, indicate at least three Holocene events at about 8-9 thousand years ago, 4-5 thousand years ago, and ~0.5-1 years ago, with the earliest event predating the terrace formation. The authors infer that the lack of a continuous soil cover and the limited storage of hillslope sediments in steep and arid bedrock landscapes limits the potential for climatic changes to cause significant valley aggradation by fluvial deposition, as seen in other landscapes.

Redefining the Metamorphic History of the Oldest Rocks in the Southern Rocky Mountains
R.F. Arnoff et al., Earth, Atmospheric, and Planetary Sciences Department, Purdue University, West Lafayette, Indiana 47907, USA. This article is online at

Our paper proves that rocks in the southern Rocky Mountains collided with North America ~150 million years later than previously thought. We employed a new age dating technique that reveals when the mineral garnet -- occasionally a gem mineral -- grew in these rocks. This is the first time this technique has been applied to rocks of this region. Our garnet ages support the hypothesis that a newly recognized mountain belt, the Picuris orogen, existed in the southwestern U.S. during the Proterozoic era. This result changes geologists' understanding of how North America formed one and a half billion years ago.

Anatomy and paleofluid evolution of laterally-restricted extensional fault zones in the Jabal Qusaybah anticline, Salakh Arc, Oman
F. Balsamo et al., NEXT - Natural and Experimental Tectonics Research Group - Department of Physics and Earth Sciences "Macedonio Melloni," University of Parma, Italy. This article is online at

We describe a peculiar type of extensional fault zones developed in the Cretaceous carbonates of the Jabal Qusaybah anticline (Oman), characterized by a complex fault network including strike-slip and extensional fault zones. Extensional faults zones are perpendicular to the fold axis, are best developed in the central sector of the anticlinal crest, and are laterally-restricted by oblique-trending strike-slip fault zones. Fault zones show widespread evidence for dilation in the form dilation breccias and calcite infillings, primarily localized at fault tips, fault overlaps, and interaction zones between strike-slip and extensional fault segments. Relative chronology and geochemical signature of fault-related veins indicate two major stages of faulting and fluid circulation during the growth of the anticline. The implication of our work is that, in this geological setting, the structural position, rather than fault displacement, is the parameter controlling the location of the more dilatants (and permeable) fault segments.

Origin of the Eastern Mediterranean: Neo-Tethys rifting along a cryptic Cadomian suture with Afro-Arabia
D. Avigad et al., Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 9190401 Israel. This article is online at

From the abstract: The Eastern Mediterranean is a land-locked basin, a remnant of the Neotethys Ocean. It was formed in the Permian-Triassic as a result of the drift of the Tauride block from the Afro-Arabian margin of Gondwana. Herein, we show that rather than being a genuine Afro-Arabia crustal fragment, the Tauride block is underlain by late Neoproterozoic Cadomian basement, which differs significantly from the Neoproterozoic "Pan-African" basement of NE Africa from which it was detached.

Stratigraphy and physical parameters of the Plinian phase of the Campanian Ignimbrite eruption
C. Scarpati and A. Perrotta, Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse. Università di Napoli "Federico II." Largo San Marcellino 10, 80138 Napoli, Italy. This article is online at

The interest in this paper result from the iconic role of the Campanian Ignimbrite in the volcanological scientific literature and on the impact of this eruption on human ecosystems (possibly leading the transition from Neanderthal to Sapiens). Our detailed stratigraphy and laboratory analyses allow us to calculate all the main physical parameters acting during the sustained column phase of this eruption. For the first time we present the complete longitudinal variation from the coarse and 10-m-thick proximal (down to 15 km) sequence, through the well stratified pumice lapilli deposit in medial areas (30 to 80 km) to the distal tephra (100s to 1000s km). The calculated magnitude of the sustained column phase is 6.3. The duration of the Plinian phase of this eruption, based on the ratio of two parameters, erupted mass divided by discharge rate, was estimated to be about 20 h (including co-Plinian ash).

Controls on gravel termination in seven distributary channels of the Selenga River delta, Baikal Rift basin, Russia
T.Y. Dong et al., Department of Earth Science, Rice University MS-126, 6100 Main Street, Houston, Texas 77005, USA. This article is online at

Here we provide science regarding the geomorphology of the Selenga River delta, Lake Baikal, Siberia, Russia. Lake Baikal is the deepest and largest lake in the world, and the Selenga River is its largest fresh-water contributor. Our research included in-depth collaborations with Russian science colleagues, and two three-week long field expeditions during the summers of 2013 and 2014. We collected several data sets that were used to evaluate water and sediment movement from the river to the lake, over the delta surface. We combined these data with analytical models to establish the timing and magnitude of sediment transfer, considering century to millennial time scales. The findings included examining how tectonic earthquake events influence the dispersal of gravel dispersal on the delta, and its effect on stratigraphy. This examination is critical to science, because deltaic stratigraphy provides a window into previous (ancient) sedimentary environments, and an opportunity to constrain climates.

Long-lived shield volcanism within a monogenetic basaltic field: the conundrum of Rangitoto Volcano, New Zealand
T. Linnell et al., School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand. This article is online at

Rangitoto volcano is located in the metropolitan area of New Zealand's largest city, Auckland. Previously, it was considered to have erupted in one short episode about 550 years ago. Therefore, it was unlikely to pose a threat to the city in the future. However, drilling through the structure of the volcano reveals an episodic history extending back thousands of years. This gives a completely new prospective on the history of the volcano and its potential to erupt in the future. These types of small basalt volcanoes are common around the world. This study and emerging research elsewhere shows that some of these volcanoes have erupted over significant time periods and erupted different types of magma. Such behavior needs to be considered in assessment of future hazards and risks.


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