Maars to calderas: end-members on a spectrum of explosive volcanic depressions

Abstract

We discuss maar-diatremes and calderas as end-members on a spectrum of negative volcanic landforms (depressions) produced by explosive eruptions (note-we focus on calderas formed during explosive eruptions, recognizing that some caldera types are not related to such activity). The former are dominated by ejection of material during numerous discrete phreatomagmatic explosions, brecciation, and subsidence of diatreme fill, while the latter are dominated by subsidence over a partly evacuated magma chamber during sustained, magmatic volatile-driven discharge. Many examples share characteristics of both, including landforms that are identified as maars but preserve deposits from non-phreatomagmatic explosive activity, and ambiguous structures that appear to be coalesced maars but that also produced sustained explosive eruptions with likely magma reservoir subsidence. A convergence of research directions on issues related to magma-water interaction and shallow reservoir mechanics is an important avenue toward developing a unified picture of the maar-diatreme-caldera spectrum.

Felsic maar-diatreme volcanoes: a review

“…The diatreme interpretation is retained here due to similarity with other felsic diatremes, lack of reported pumice in the dominant vent fill, and small size relative to many calderas. However, Cerro de Pasco is the largest diatreme reviewed here in detail and is the only one showing clear evidence of a magmatic explosive style for a significant portion of its eruptive history (see below), suggesting that it may indeed be a 'hydrid' between a maar-diatreme and a caldera, of the type proposed by Palladino et al (2015).…”

“…Several writers have stated that felsic maar-diatremes are phreatomagmatic volcanoes (e.g., Sillitoe and Bonham 1984;Sillitoe 1985;Brooker and Jaireth 1995;Carrasco-Núñez and Ort 2012;Lorenz and Suhr 2012;Palladino et al 2015), partly by analogy with their ultramafic to mafic counterparts. Using only evidence summarized in this review and relating to felsic maardiatremes, phreatomagmatism must be the dominant eruptive style to explain the following features: (i) deep diatremes (sometimes over 1 km deep) with abundant lithic clasts, signifying efficient country rock fragmentation; (ii) evidence for water in the eruption column and deposits of the ejecta ring, such as bomb sags, accretionary lapilli, or tuff with soft-sediment deformation; (iii) dense to poorly vesicular juvenile clasts being typical of, or abundant in, the ejecta ring and diatreme; (iv) at Tepexitl, juvenile ash in the 4 phi size fraction being dominated by dense blocky particles with features such as stepped fractures, branching quench cracks, and pitting.…”

“…The smallest calderas overlap in size with the largest felsic maar-diatremes (Nemeth et al 2009;Lorenz and Suhr 2012;Palladino et al 2015). They are both characterized by more or less circular depressions surrounded by a relatively thin package of pyroclastic deposits.…”

Corrigendum: Maars to calderas: end-members on a spectrum of explosive volcanic depressions

“…In the original article (Palladino et al, 2015), there was an error in Figure 1. The vertical axis of the qualitative plot reported erroneously "ratio of juvenile to lithic materials in deposits outside of depression".…”

The effects of the host-substrate properties on maar-diatreme volcanoes: experimental evidence

“…Beneath the crater in the subsurface, a diatreme structure extends downward as a cone-shaped body of fragmented country rocks, juvenile materials and magmatic intrusions (Lorenz 1973(Lorenz , 1986White and Ross 2011 and references therein). Maar-diatremes are an end-member type of explosive volcanic depression (Palladino et al 2015), formed by discrete subsurface explosions that brecciate and eject country rock and juvenile material onto their tephra rings. Although maar-diatremes also typically have important components of subsidence due to explosion processes (e.g., Sweeney and Valentine 2015) and diatreme fill compaction, they are distinguished from explosive calderas, which form almost entirely by subsidence due to magma withdrawal with only minor components of country rock ejection.…”