Trends in maar crater size and shape using the global Maar Volcano Location and Shape (MaarVLS) database

Abstract

A maar crater is the top of a much larger subsurface diatreme structure produced by phreatomagmatic explosions and the size and shape of the crater reflects the growth history of that structure during an eruption. Recent experimental and geophysical research has shown that crater complexity can reflect subsurface complexity. Morphometry provides a means of characterizing a global population of maar craters in order to establish the typical size and shape of features. A global database of Quaternary maar crater planform morphometry indicates that maar craters are typically not circular and frequently have compound shapes resembling overlapping circles. Maar craters occur in volcanic fields that contain both small volume and complex volcanoes. The global perspective provided by the database shows that maars are common in many volcanic and tectonic settings producing a similar diversity of size and shape within and between volcanic fields. A few exceptional populations of maars were revealed by the database, highlighting directions of future research to improve our understanding on the geometry and spacing of subsurface explosions that produce maars. These outlying populations, such as anomalously large craters (> 3000 m), chains of maars, and volcanic fields composed of mostly maar craters each represent a small portion of the database, but provide opportunities to reinvestigate fundamental questions on maar formation.Maar crater morphometry can be integrated with structural, hydrological studies to investigate lateral migration of phreatomagmatic explosion location in the subsurface. A comprehensive

Recent volcano-tectonic activity of the Ririba rift and the evolution of rifting in South Ethiopia

“…Maar craters are generally an order of magnitude wider than those of the other monogenetic volcanic edifices, having an average H cr /W cr = 0.1 (Tab. S2e of Supplementary material), in agreement with the mean value reported in the MaarVLS Database (Graettinger et al, 2018). Due to the high explosivity and depth of explosion, the associated deposits are characterised by the presence of a huge number of deep-seated xenoliths, variable in size (up to m-sized bombs), torn out from the walls of the diatreme (metamorphic basement) or directly transported from the source region (mantle-derived xenoliths), a typical feature observed also in other maars (e.g., Saucedo et al, 2017).…”

“…The evident clustering of maars in the Dilo VF and their alignment along structural lineaments also suggest an important control of deep-seated structures on this activity, in agreement with the average Elongation value (EL, Tab. S2e of Supplementary material) lower than the value calculated by Graettinger (2018) for the global maar database (0.70-0.75 vs. 0.81, respectively). We can so conclude that the most prominent role of phreatomagmatic activity, the generally higher explosivity of the activity, and the less abundant effusive activity in the Dilo VF respect to the Mega VF are possible indications of differences in the primary magmatic explosivity of erupted magma and of a different subsurface structural setting for the two VFs, which control the final magma ascent to the surface.…”

“…Lava flows are never found associated with these maars, according to the general features of maar volcanism. Especially in the Dilo VF, maars generally occur in clusters, arranged along regional lineaments and sometimes with overlapping explosion footprints, resulting in compound crater shapes with septa (ridges separating low points in a compound crater) and complex tephra rings (Graettinger et al, 2018). The observed depth and internal slopes of the maars are generally the result of a post-eruptive modification by erosional retreat of the wall and post-eruption infill of the crater.…”

Phreatomagmatic vs magmatic eruptive styles in maar-diatremes: a case study at Twin Peaks, Hopi Buttes volcanic field, Navajo Nation, Arizona

“…Around the world, maar-diatremes are found in active monogenetic volcanic fields, some of which are located near large cities such as Auckland, New Zealand (Németh et al 2012;Németh and Kereszturi 2015;Nunns and Hochstein 2019) or Goma, Democratic Republic of Congo (Poppe et al 2016). Maar-diatreme volcanoes comprise a subaerial part composed of an ejecta ring (Self et al 1980;Vazquez and Ort 2006;Valentine et al 2015) and a maar crater (Lorenz 1973;Graettinger 2018). Their subterranean part is composed of an upper typically bedded diatreme Gernon et al 2013;Delpit et al 2014), an upper/lower diatreme transition zone (Bélanger and Ross 2018;Latutrie and Ross 2019), a lower nonbedded diatreme Lefebvre et al 2013Lefebvre et al , 2016, a root zone (Clement 1982;Lorenz and Kurszlaukis 2007;Haller et al 2017) and a feeder intrusion (Re et al 2015(Re et al , 2016Muirhead et al 2016;Le Corvec et al 2018).…”

Transition zone between the upper diatreme and lower diatreme: origin and significance at Round Butte, Hopi Buttes volcanic field, Navajo Nation, Arizona

“…Due to exposure constraints, most maar-diatreme studies focus on a specific part of the volcano, such as the ejecta ring and crater (e.g., Kienle et al 1980;White 1991;Vazquez and Ort 2006;Ort and Carrasco-Núñez 2009;Austin-Erickson et al 2011;Valentine et al 2015;Graettinger 2018), the upper diatreme (e.g., White 1991;White and Ross 2011;Delpit et al 2014), the lower diatreme (e.g., White 1991;Lefebvre et al 2013Lefebvre et al , 2016Bélanger and Ross 2018), or rarely, the root zone (Clement 1982;Lorenz and Kurszlaukis 2007) or the intrusive plumbing system (Re et al 2015(Re et al , 2016Muirhead et al 2016;Le Corvec et al 2018). The origin of the lower diatreme is still strongly debated in the literature (see discussion in Bélanger and Ross 2018).…”