What is the difference between criteria and caldera

Cartoons, which are drawn approximately to scale, are intended to show the depressions just after formation, and thus do not show post-eruption sediments or caldera resurgent features. See Table 1 for examples across the spectrum. Table 1. Volcanic depression types on spectrum from hydrothermal explosion craters to large explosive calderas.

An idealized explosive caldera end-member Figure 1 ; Table 1 forms by subsidence during withdrawal of a few to thousands of cubic kilometers of magma during sustained high-discharge-rate eruption. Deposits around calderas can include widely dispersed fallout beds, but the bulk of the products are usually preserved in ignimbrites that are relatively massive and poorly sorted.

Juvenile components in the form of pumice coarse-ash to block sizes and vitric ash medium to fine ash sizes dominate the deposits. Although lithic-rich domains can be abundant in proximal facies co-ignimbrite lag breccias; Druitt, ; Walker, , in local concentrated zones, and as isolated clasts throughout the extent of an ignimbrite, the lithics are overall a minor component compared to juvenile particles.

Calderas range from several kilometers to several tens of kilometers in diameter, with subsidence depths from a few m to a few kilometers Acocella, Beneath the surface expressions of calderas are thick accumulations of intracaldera ignimbrite, often exceeding 1 km thickness, with interstratified breccias and megabreccias associated with caldera collapse Lipman, , Intrusions include dikes, sills, and stocks. Many calderas, especially the larger ones, have some sort of structural or eruptive resurgence during the tens of thousands of years after collapse that results in a raised central portion not shown in Figure 1.

Most calderas are related to magmatic systems that have life spans of hundreds of thousands to a million years, and result from multiple, hours- to days-long caldera-forming eruptions.

However, a given caldera forms during a single eruptive episode, as does a maar-diatreme recognizing that many caldera clusters are the products of multiple, overlapping calderas formed during different episodes. Both maars and calderas are produced by volcanic and hypabyssal intrusive processes, but typically also contain sedimentary deposits that are characteristic of steep-sided, closed basins.

Many volcanoes that are identified as maars included eruptive phases with little or no involvement of external water, and with sustained discharge of mainly juvenile material.

This magmatic volatile-driven activity may occur in either early or late phase of a maar-forming event, or may alternate repeatedly with phreatomagmatic phases e. Often it is preserved as scoria lapilli fallout horizons within tephra ring sequences, and can be traced to distances that exceed the main tephra ring deposits that were mainly emplaced by pyroclastic surges and ballistics. The fallout beds are characteristic of sustained Hawaiian, violent Strombolian to sub-Plinian eruption columns.

For example, the ultrapotassic Albano multiple maar hosted repeated cycles of eruptive activity through 35 kyrs, reaching estimated maximum column height of 18—21 km and corresponding peak magma discharge rate up to 2.

Most volcanoes of this type involve relatively mafic magmas, for which the criteria to assess the phreatomagmatic vs. In some examples scoria cones, produced mainly by Strombolian activity, and lavas are preserved on maar crater floors e. These record ascent of magma batches through a diatreme with minimal interaction with groundwater; however, the main landforms—maars and tephra rings and underlying diatremes—were produced by discrete phreatomagmatic explosions.

Although magmatic volatile-driven, sustained eruption played a role, these examples are near the maar end-member. In other examples Table 1 , usually involving the eruption of more silicic magmas, sustained activity becomes more significant and may prevail even though their landforms are similar to those of end-member maar-diatremes. Commonly, trachytic and phonolitic examples in central Italy have tephra rings and maar-like craters, and their deposits are dominated by fine-grained, moderately to highly vesicular juvenile clasts and very few lithic clasts, most of which were emplaced ballistically.

Except for the relatively fine-grained nature of the deposits, typical indicators of phreatomagmatic explosions and fragmentation, such as high lithic contents and blocky, poorly vesicular ash grains with quench cracks, may be lacking. This brings ambiguity to interpretation of magma fragmentation and eruption mechanisms.

Silicic examples include both tuff ring and maar-like systems, such as Averno 2 in the Campi Flegrei with 0. Wider depressions are transitional to calderas. Laacher See depression Eifel, Germany , about 3 km in diameter, is identified by Freundt and Schmincke as a maar, despite the unusually high volume 16 km 3 of loose deposits and dispersal of phonolitic tephra, and the dominance of deposits from inferred magmatic volatile-driven vs.

Similarly, deposits associated with identified calderas often show some evidence of significant phreatomagmatic explosions. Detailed studies of eruptive products of calderas such as Askja Iceland; Self and Sparks, ; Carey et al.

In these and other cases, the presence of very fine-grained fallout beds with abundant accretionary lapilli might indicate water-assisted fragmentation, although there is uncertainty associated with the attribution of phreatomagmatic origin based mainly on the high degree of magma fragmentation Palladino and Taddeucci, ; Dellino et al.

Latera volcano Vulsini Volcanic District, Italy is an example that had several caldera-forming eruptions, each of which produced ignimbrites with volumes on the order of several cubic kilometers. Such cases record volumetrically minor phases in individual caldera-forming eruptions that are otherwise dominated by sustained discharge of juvenile material e. The main process responsible for caldera formation in all of these cases was syn-eruptive subsidence over a large magma reservoir.

Although phreatomagmatic activity played a role, these volcanoes are near the caldera end-member. We suggest that it is important to think about maar-diatremes and explosive calderas in the context of a spectrum of behaviors. Such a framework highlights key problems that, from our perspective, should be major topics of research in the volcanological community.

MFCI is favored by: 1 low melt viscosity mafic rather than silicic magmas because a large viscosity contrast between melt and water acts against premixing; 2 small magma batches, which more easily premix and are emplaced rapidly into the hypabyssal environment with minimal time for degassing and crystallization; 3 low overall magma fluxes which favor the intrusion of small batches of magma and do not overwhelm available water; and 4 low melt vesicularity Zimanowski et al. All of these conditions are most likely to be met in small, monogenetic, mafic volcanoes and indeed most maars that approach end-member behavior are of that type.

Valentine et al. Mafic monogenetic volcanoes often do not have shallow magma reservoirs but are fed by magmas that ascend from depths of tens of kilometers to the surface, which reduces the role of surface subsidence due to magma withdrawal, although subsidence can occur by post-eruptive compaction of diatreme fill.

Explosive calderas involve large volumes of magma that evolves in long-lived crustal reservoirs with country rock roofs that subside, mainly bounded by faults e. Melt viscosity is normally relatively high, and bubbles that form as magma ascends are coupled with the melt, promoting in turn the formation of pumice and ash during sustained high-flux discharge that is very different from the discrete explosions caused by MFCI. All of these aspects in fact act against magma-water interaction within the context of MFCI, and we urge caution in applying concepts such as optimal magma-water ratios and the classical ash morphology criteria e.

Is the process feasible up to phreatoplinian scale? Is magma vesiculation, which might reduce the magmastatic pressure at a given depth in a conduit by reducing the mixture density so that it falls below the local hydrostatic pressure, important in allowing for mixing of phreatic water into a conduit with active magma flow?

Although extra fragmentation by interaction with externally derived water is often inferred e. This is a major and difficult-to-address gap in our understanding that deserves focused research. Volcanic depressions that fall toward the middle of the spectrum Figure 1 have different combinations of components of the end-members. Maar-diatremes that were formed by repeated discrete explosions but that preserve evidence for a component of subsidence due to magma withdrawal probably formed above shallow, relatively short-lived decades?

Questions that need to be addressed to understand this intermediate case include the mechanisms of formation and magma evolution within shallow sills, and mechanisms and rates of leakage from them. Other intermediate systems appear to have had longer-lived magma reservoirs, which occasionally leaked small batches of magma that formed end-member type maars.

In such cases the magma reservoir itself may act as a filter that promotes conditions for phreatomagmatic explosions above it, as magma ascending from depth in higher-flux batches is mostly trapped in the reservoir. The maars can form at different locations above the reservoir and their depressions may overlap to form a larger composite depression that also has a subsidence component produced by episodes of sustained, magmatic volatile-driven discharge. If caldera-bounding faults formed during such an event, subsequent low-flux leaks may be focused along the faults, producing the type of phreatomagmatic circum-caldera deposits at Latera caldera, described above.

Again, the mechanisms and rates of leakage from the shallow reservoirs is a key problem to address. Products of sustained-discharge eruptions that are inferred to have also had significant magma-water interaction are subject to the same cautions raised above for calderas.

Active geologic processes associated with the Yellowstone hotspot are fundamental in shaping the landscapes of the greater Yellowstone ecosystem GYE , a high volcanic plateau flanked by a crescent of still higher mountainous terrain. The processes associated with the Yellowstone hotspot are volcanism, faulting, and uplift and are observed in the When the violent energy of a volcano is unleashed, the results are often catastrophic.

The risks to life, property, and infrastructure from volcanoes are escalating as more and more people live, work, play, and travel in volcanic regions.

Since , 45 eruptions and 15 cases of notable volcanic unrest have occurred at 33 U. Although no eruptions of lava or volcanic ash have occurred for many thousands of years, future eruptions are likely. In the next few hundred years, The cataclysmic eruption of Mount St. Helens Lipman and Mullineaux, in southwestern Washington ushered in a decade marked by more worldwide volcanic disasters and crises than any other in recorded history.

Volcanoes killed more people over 28, in the 's than during the 78 years following eruption of Mount Pelee Kenneth Pierce studied the geology and geomorphology of the greater Yellowstone area for nearly his entire career with the U. Geological Survey. From to present, Dr. Pierce has mapped glacial deposits, pioneered Quaternary dating techniques, conducted research on the Yellowstone Hot Spot, studied the geothermal areas, explored the geology of archaeological sites.

A caldera is a large, usually circular volcanic depression formed when magma is withdrawn or erupted from a shallow underground magma reservoir. It is often difficult to visualize how calderas form. This simple experiment using flour, a balloon, tubing, and a bicycle pump, provides a helpful visualization for caldera formation.

Giant ash cloud from the eruption of Mount Pinatubo, towering above farms and agricultural lands in the Philippines. Skip to main content. Search Search. Natural Hazards. Learn more: Caldera systems--a worldwide family that is more than just Yellowstone! A personal commentary: Why I dislike the tern "supervolcano" and what we should be saying instead. Apply Filter. Is Yellowstone overdue for an eruption? When will Yellowstone erupt?

Yellowstone is not overdue for an eruption. Volcanoes do not work in predictable ways and their eruptions do not follow predictable schedules.

In terms of large explosions, Yellowstone has experienced three at 2. This comes out What type of eruption will Yellowstone have if it erupts again? The most likely explosive event to occur at Yellowstone is actually a hydrothermal explosion —a rock-hurling geyser eruption—or a lava flow. Hydrothermal explosions are very small; they occur in Yellowstone National Park every few years and form a crater a few meters across.

Every few thousand years, a hydrothermal explosion will form a crater as What was the largest volcanic eruption in the 20th century? The world's largest eruption of the 20th century occurred in at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6th. This nascent rift [ 44 , 45 ], at the origin of the Cameroon Volcanic Line in general and of Mount Bambouto and its respective caldera system in particular, is of the extensional type and their code is EXT.

A Pre-caldera regional dome occurred through a tumescence that created numerous concentric faults. These fissures favored a pre-caldera magmatic activity that further contributed to the building of the Bambouto stratovolcano. Its code is therefore STR. The collapse of the Caldera of Mount Bambouto occurred at the beginning of the sequence of eruptions that contributed to their formation.

Their code is A. In the Mount Bambouto, this volcanic activity is dominated by the presence of several eruptive vents, notably on the ramparts, the eastern floor of the caldera and the NE slope of the volcano. On the other hand, the ramparts of the Mount Bambouto Caldera are threatened by growing urbanization and agro-pastoral activity, particularly to the south and east of the caldera.

Its boundaries are therefore slightly destroyed. Its code is PD. Through the mode of outcropping of different rocks in the caldera of Mount Bambouto, all types of dynamism extrusive, effusive, explosive exist in the caldera.

These are therefore polygenic volcanoes marked by long periods of activity and varied dynamisms, resting and erosion phases during different tectonic episodes [ 46 ]. In addition, the diversity of rocks is indicative of the high degree of magma differentiation induced here by the fractional crystallization process [ 21 , 47 , 48 ].

The presence of the trachytes in ignimbrites of the study area is an indicator of a relative chronology of the rocks. Indeed, there was an ante-ignimbritic trachytic volcanic phase. This means that there has been in the course of the evolution of the Bambouto volcano, the eruption of trachytic rocks before that of ignimbritic materials [ 49 , 50 ]. The caldera of Mount Bambouto was formed at a well-defined time. The stages of formation of these calderas correspond globally to the model of [ 9 ]: a regional tumescence, a volcanic eruption, a collapse of the caldera, volcanism on the annular fractures and sedimentation.

The present structure of the caldera floor shows that the roof of the magma chamber collapsed piecemeal during its formation. The border faults generally observed on calderas in certain volcanic environments in Cameroon, which are evidence of the different phases of caldera collapse, are difficult to observe in the caldera of Mount Bambouto.

These faults, when identifiable on certain ramparts, present a some stages of collapse Figure 3. In this caldera, the ramparts are often confused with the floor.

The latter constitutes the most dissected floor of all the caldera units studied along the Cameroon Volcanic Line and their arrangement in decreasing steps from west to east, would testify to the multiple collapses that marked its formation [ 51 , 52 ]. On the other hand, in the Eboga and Lefo calderas, where the ramparts are clearly visible from the caldera floor, there are boundary faults marked by about 2—4 stages of collapse [ 29 ].

Post-caldera volcanism has manifested itself on the Mount Bambouto. It is at the origin of numerous doleritic, phonolitic and trachytic protrusions and, cones and maars found on the floor and external slopes of these calderas [ 33 , 51 , 52 , 53 , 54 ].

These post-caldera geomorphological units give the caldera of Mount Bambouto the S and MS types according to [ 14 ]. Mount Bambouto constitutes a stratovolcano [ 20 , 33 ]. This shape results from the geometry of the magma chamber which is the main factor controlling the final morphology of the calderas [ 58 ]. The presence of ignimbrites, tuffs, trachytes and rhyolites in the caldera of the Mount Bambouto qualifies it as an ignimbrite caldera. Ignimbrite calderas are usually over 10 km in diameter and over 1 km in depth, formed after the voluminous deposition of silicic ignimbrites [ 9 , 11 , 59 ].

Their presence in Mount Bambouto is explained by the fact that, considering the ages, this massif is sufficiently old compared to the other massifs, especially Mount Manengouba, because these acid magmas, according to [ 62 ], require a significant period of time for their formation to be elaborated. Calderas are places where several natural hazards occur, including volcanic eruptions and mass movements [ 63 , 64 ].

According to [ 65 ], calderas are destructive volcanic forms because they cause pre-existing reliefs to collapse, unlike post-caldera cones and domes, which are constructive because pre-existing reliefs are put in place. Moreover, the volcanic formations that cover them favor the formation of fertile soils and the development of a plant cover of various species conducive to an agropastoral activity [ 16 ].

These are environments where hydrothermal activities and mineralization processes generally occur [ 57 , 66 , 67 ]. In this respect, it is clear that calderas have a strong educational value as they allow us to understand the complexity of certain craters in volcanic environments around the world.

As such, they allow us to understand the degree of fracturing of the ante-caldera substratum, the superposition of eruptive products and the slices of the flows at the ramparts and the post-eruptive geological processes. Thus, calderas are often the seat of later volcanic activities that leave exceptional geomorphological units with several values suitable for geotourism [ 33 , 51 , 52 , 56 , 73 , 74 , 75 ]. The Caldera of Mount Bambouto is a volcanic unit that formed at a period between Its emplacement model is comparable to that of Cole et al.

Its formation and evolution gave it a rather varied petography and a characteristic structure. Its classification according to the Caldeira DataBase of Geyer and Marti allows us to conclude that its type of collapse is piecemeal. Furthermore, this caldera was formed through a continental rifting of extensional type, and their postcaldera protrusions give them Type-S and Type-MS. Moreover, it is a well-preserved caldera because its ridge lines are well observable. The classification of the caldera of Mount Bambouto made within the framework of this work makes it possible to understand the similarities of this caldera with other calderas around the world on the one hand and to understand part of the global dynamics of the functioning of the Cameroon Volcanic Line on the other hand.

Furthermore, this study contributes to elucidate the origin of the Cameroon Volcanic Line, which is still a subject of discussion among Cameroonian and foreign researchers today. Moreover, through this work, the Mount Bambouto Caldera is promoted next to the world scientific community that is still ignoring his existence. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.

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