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Types of collapse calderas. Three main types of collapse calderas can be defined, 1 summit caldera : those formed at the top of large volcanoes, 2 classic caldera : semi-circular to irregular-shaped large structures, several km in diameter and related to relatively large-volume pyroclastic products, and 3 graben caldera : explosive volcano-tectonic collapse structures from which large-volume, ignimbrite-forming eruptions occurred through several fissural vents along the graben master faults and the intra-graben block faults.
These in turn can collapse at least with three styles: 1 Piston: when the collapse occurs as a single crustal block; 2 Trap-door: when collapse occurs unevenly along one side while the opposite side remains with no collapse; 3 Piece-meal: when collapse occurs as broken pieces of the crust on top of the magma chamber.
Caldera -formation is one of the most awe-inspiring and powerful displays of nature's force. Resultant deposits may cover vast areas and significantly alter the immediate topography. Post-collapse activity may include resurgence, unrest, intra- caldera volcanism and potentially the start of a new magmatic cycle, perhaps eventually leading to renewed collapse.
Since volcanoes and their eruptions are the surface manifestation of magmatic processes, calderas provide key insights into the generation and evolution of large-volume silicic magma bodies in the Earth's crust. Despite their potentially ferocious nature, calderas play a crucial role in modern society's life. Collapse calderas host essential economic deposits and supply power for many via the exploitation of geothermal reservoirs, and thus receive considerable scientific, economic and industrial attention.
Calderas also attract millions of visitors world-wide with their spectacular scenic displays. To build on the outcomes of the calderas workshop in Tenerife Spain and to assess the most recent advances on caldera research, a follow-up meeting was proposed to be held in Mexico in The multi-disciplinary workshop was attended by more than 40 scientist from North, Central and South America, Europe, Australia and Asia.
Searching for patterns in caldera unrest. The ultimate goal of volcanology is forecasting eruptions. This task is particularly challenging at calderas , where unrest is frequent, affects wider areas and its evidence is often masked by the activity of hydrothermal systems.
A recent study has compiled a database on caldera unrest, derived from seismicity, geodetic, gravity, and geochemical monitoring data at calderas worldwide, from to Here we exploit this database, searching for the most recurring features of unrest and, in turn, its possible dynamics. In particular, we focus on a the duration of unrest at calderas ; b recurring patterns in unrest; c unrest episodes culminating in eruptions, including time-predictability or size-predictability and a multivariate regression analysis.
Our analysis suggests that magma may withstand only a limited period of "eruptability," before becoming stored in the upper crust. Calderas and mineralization: volcanic geology and mineralization in the Chianti caldera complex, Trans-Pecos Texas. This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas.
Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some and denied by others. Steven and others have demonstrated that calderas provide an important setting for mineralization in the San Juan volcanic field of Colorado.
Mineralization is not found in all calderas but is apparently restricted to calderas that had complex, postsubsidence igneous activity. A comparison of volcanic setting, volcanic history, caldera evolution, and evidence of mineralization in Trans-Pecos to those of the San Juan volcanic field, a major mineral producer, indicates that Trans-Pecos Texas also could be an important mineralized region.
The Chianti caldera complex in Trans-Pecos Texas contains at least two calderas that have had considerable postsubsidence activity and that display large areas of hydrothermal alteration and mineralization. Abundant prospects in Trans-Pecos and numerous producing mines immediately south of the Trans-Pecos volcanic field in Mexico are additional evidence that ore-grade deposits could occur in Texas.
Stress evolution during caldera collapse. The mechanics of caldera collapse are subject of long-running debate. Particular uncertainties concern how stresses around a magma reservoir relate to fracturing as the reservoir roof collapses, and how roof collapse in turn impacts upon the reservoir.
We used two-dimensional Distinct Element Method models to characterise the evolution of stress around a depleting sub-surface magma body during gravity-driven collapse of its roof.
These models illustrate how principal stress orientations rotate during progressive deformation so that roof fracturing transitions from initial reverse faulting to later normal faulting. They also reveal four end-member stress paths to fracture, each corresponding to a particular location within the roof. Analysis of these paths indicates that fractures associated with ultimate roof failure initiate in compression i.
We also report on how mechanical and geometric conditions in the roof affect pre-failure unloading and post-failure reloading of the reservoir. In particular, the models show how residual friction within a failed roof could, without friction reduction mechanisms or fluid-derived counter-effects, inhibit a return to a lithostatically equilibrated pressure in the magma reservoir.
Many of these findings should be transferable to other gravity-driven collapse processes, such as sinkhole formation, mine collapse and subsidence above hydrocarbon reservoirs. Composite Calderas : The Long and Short of it. Calderas formed in supereruptions are normally linked to a single magma body. However, caldera formation, regional tectonics, and multiple magma bodies may interact to form composite structures with complex geometries.
Three examples of composite caldera styles from New Zealand and Japan show field, geophysical, geochemical and isotopic evidence to suggest that current models for the size, shape and evolution of calderas may be too simplistic. In our examples, multiple separate magma bodies distributed in either space or time, or both, may play a significant role in composite caldera formation. Multiple, clustered collapse events incremental in time: Akan caldera in Hokkaido appears to be a single, rectangular shaped caldera.
New gravity data shows that the caldera is actually a daisy-chain of 3 distinct collapse structures that can be correlated, using lithic componentry, to 3 major geochemical groups in the eruptive products.
Multiple, clustered collapse events in a single eruption sequence: Shikotsu caldera in Hokkaido was originally thought to have formed following the eruption of a single large zoned magma chamber.
However, the caldera -related deposits are characterized by several geochemically distinct pumice types that can not have been accommodated in a single magma system. Our studies suggest that the variations in pumice compositions are consistent with multiple distinct magma bodies feeding coeval eruptions from several vent sources within an area that collapsed to form a single caldera.
Paired calderas with linking eruption-related regional faulting: Rotorua and Ohakuri calderas in New Zealand are 30 km apart and formed in close succession during a complex but virtually continuous eruption sequence at ca. Origin of calderas : discriminating between collapses and explosions. Directory of Open Access Journals Sweden. Full Text Available Origins of calderas may differ according to their subsurface structure that may be characterized by high or low density deposits that may be observed as high or low gravity anomalies, respectively.
Coincidently, these four calderas are all low-gravity-anomaly type. These results are confirmed by results of drillings at some other calderas. Then, caldera formation of both types is discussed: High-gravity-anomaly-type calderas are expected to originate from subsidence of high-density ejecta into the summit magma reservoir. On the calderas of this type, the genetic eruptions believed to be accompanied by subsidences were not actually observed, and consequently three examples are mentioned only briefly.
The low-gravity-anomaly-type calderas are discussed from standpoint of both the models of collapses and explosions. It is also emphasized that dynamic pressure ofexplosions is an important factor in the caldera formation, not only volume of the ejecta.
To confirm the possibility that volcanic ejecta and edifices collapse into magma reservoirs, we discuss stress propagation from a depleted reservoir upward towards the Earth surface. Formation mechanisms of large calderas of this type are speculated; large calderas measuring about 20 km across may develop by successive merging of component calderas over a long period of times.
A Kamchatka caldera under enlargement during the Holocene period is interpreted by successive merging of five component calderas. Caldera resurgence driven by magma viscosity contrasts. Calderas are impressive volcanic depressions commonly produced by major eruptions. Equally impressive is the uplift of the caldera floor that may follow, dubbed caldera resurgence, resulting from magma accumulation and accompanied by minor eruptions.
Why magma accumulates, driving resurgence instead of feeding large eruptions, is one of the least understood processes in volcanology. Here we use thermal and experimental models to define the conditions promoting resurgence. Thermal modelling suggests that a magma reservoir develops a growing transition zone with relatively low viscosity contrast with respect to any newly injected magma.
Experiments show that this viscosity contrast provides a rheological barrier, impeding the propagation through dikes of the new injected magma, which stagnates and promotes resurgence. In explaining resurgence and its related features, we provide the theoretical background to account for the transition from magma eruption to accumulation, which is essential not only to develop resurgence, but also large magma reservoirs.
Post-supereruption recovery at Toba Caldera. Large calderas , or supervolcanoes, are sites of the most catastrophic and hazardous events on Earth, yet the temporal details of post-supereruption activity, or resurgence, remain largely unknown, limiting our ability to understand how supervolcanoes work and address their hazards.
Since the supereruption, Toba has been in a state of resurgence but its magmatic and uplift history has remained unclear. The major stratovolcano north of Toba, Sinabung, shows strong geochemical kinship with Toba, and zircons from recent eruption products suggest Toba's climactic magma reservoir extends beneath Sinabung and is being tapped during eruptions.
Geomorphological classification of post- caldera volcanoes in the Buyan-Bratan caldera , North Bali, Indonesia. A landform of the post- caldera volcanoes Lesung, Tapak, Sengayang, Pohen, and Adeng in the Buyan-Bratan caldera on the island of Bali, Indonesia can be classified by topographic interpretation. The Tapak volcano has three craters, aligned from north to south. Lava effused from the central crater has flowed downward to the northwest, separating the Tamblingan and Buyan Lakes.
This lava also covers the tip of the lava flow from the Lesung volcano. Therefore, it is a product of the latest post- caldera volcano eruption. The Lesung volcano also has two craters, with a gully developing on the pyroclastic cone from the northern slope to the western slope. Lava from the south crater has flowed down the western flank, beyond the caldera rim.
Lava distributed on the eastern side from the south also surrounds the Sengayang volcano. The Adeng volcano is surrounded by debris avalanche deposits from the Pohen volcano. Based on these topographic relationships, Sengayang volcano appears to be the oldest of the post- caldera volcanoes, followed by the Adeng, Pohen, Lesung, and Tapak volcanoes.
Coarse-grained scoria falls around this area are intercalated with two foreign tephras: the Samalas tephra A. The source of these scoria falls is estimated to be either the Tapak or Lesung volcano, implying that at least two volcanoes have erupted during the Holocene period. Lithium deposits hosted in intracontinental rhyolite calderas. Lithium Li is classified as a technology-critical element due to the increasing demand for Li-ion batteries, which have a high power density and a relatively low cost that make them optimal for energy storage in mobile electronics, the electrical power grid, and hybrid and electric vehicles.
Given that many projections for Li demand exceed current economic reserves and the market is dominated by Australia and Chile, discovery of new domestic Li resources will help diversify the supply chain and keep future technology costs down. Here we show that lake sediments preserved within intracontinental rhyolite calderas have the potential to host Li deposits on par with some of the largest Li brine deposits in the world.
We compare Li concentrations of rhyolite magmas formed in a variety of tectonic settings using in situ SHRIMP-RG measurements of homogenized quartz-hosted melt inclusions. Rhyolite magmas that formed within thick, felsic continental crust e. When the Li-enriched magmas erupt to form calderas , the cauldron depression serves as an ideal catchment within which meteoric water that leached Li from intracaldera ignimbrite, nearby outflow ignimbrite, and caldera -related lavas can accumulate.
Additional Li is concentrated in the system through near-neutral, low-temperature hydrothermal fluids circulated along ring fractures as remnant magma solidifies and degasses. Li-bearing hectorite and illite clays form in this alteration zone, and when preserved in the geological record, can lead to a large Li deposit like the 2 Mt Kings Valley Li deposit in the McDermitt Caldera , Nevada. Because more than large Cenozoic calderas occur in the western United States that formed on eruption.
Petrological cycles and caldera -forming events. Many caldera -forming events can be framed within broad petrological cycles; volcanic stratigraphy typically defines a trend from mafic to more silicic magmas with time, culminating in the catastrophic evacuation of an upper crustal reservoir filled with the silicic magma, followed by a return to the eruption of more mafic magmas shortly after caldera collapse.
Understanding how such cycles develop has clear implications for characterizing the current state of an active system.
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