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Igneous activity and landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Cryptovolcanic features are circular low domes or depressions, some 3–12 km in diameter, with little or no ejecta, believed to result from explosions of volcanic gases near the surface. Eight have been identified in the United States. Some consist of a central uplift with a marginal depression cut by a radial and concentric pattern of normal tension faults, but others like the Rieskessel basin in Germany have a calderalike expression. Smaller structures are the roughly circular explosion craters or maars (German, ‘lake’) which generally have diameters of 500 m to about 1 km, are less than 150 m deep and have low raised rims of 4° outward slope. Maars are quite widespread in the Eifel district of Germany, New Zealand, Luzon and elsewhere, but an especially large one is Hole-in-the-Ground, Oregon (1500 m diam. and 130 m deep). It has been suggested that some maars may have been formed by the explosive mixing of rising magma and groundwater, or by degassing to produce diatremes and flat-floored fluidization craters (Figure 6.26).
Volcanoes and Their Products
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
On continents, hydrovolcanic eruptions may produce shallow craters called maars, often surrounded by unconsolidated deposits called tuff rings. Figure 7.32 shows a maar and tuff ring at Kilbourne Hole, in the Potrillo Volcanic Field of New Mexico. Maars form when an explosive eruption creates a broad flat- bottomed hole in the ground, and tuff rings—a little like dunes—contain material ejected during the explosion. The tuff rings at Kilbourne Hole appear as narrow ridges that surround the shallow crater. The tuff lies on top of black basalt that predates the maar formation. Maars range in size from 60 to 8000 meters in diameter and 10 to 200 meters in depth. The maar shown here is a relatively small one.
The role of hydrovolcanism in the formation of the Cenozoic monogenetic volcanic fields of Zealandia
Published in New Zealand Journal of Geology and Geophysics, 2020
The macroforms of small volume volcanoes such as maar craters (Figure 2A), tuff rings (Figure 2B) or tuff cones (Figure 2C) are commonly used to infer hydrovolcanic processes responsible for the growth of those macroforms (Morrissey et al. 2000; Brand and Brož 2015; Brož and Németh 2015; De Hon 2015; de Silva and Lindsay 2015; Valentine and Connor 2015; White et al. 2015). Recent research, however, has demonstrated that the process of cratering, for instance the formation of a maar, should be looked at as process creating the volcanic macroform that may or may not be linked to an explosive magma – water interaction hence hydrovolcanism, or more specifically to phreatomagmatism (Graettinger et al. 2015, 2016; Graettinger and Valentine 2017). Here we use maar as a volcanic landform that consists of a flat floored crater cut into the syn-volcanic landscape (even if it is rugged) creating a ‘hole-in-the-ground’ morphology (Christenson et al. 2015; Graettinger 2018; Németh and Kósik 2020), without linking it directly to explosive phreatomagmatic eruptions. Some reports suggest that dry maar craters may form in response to a gas-rich magma subterranean explosion (Mattsson 2012; Berghuijs and Mattsson 2013; Balashova et al. 2016). However, the preserved tephra rings that surround a maar crater show many microtextural features indicative of magma and water interaction, hence phreatomagmatism (Graettinger 2018; Ort et al. 2018).
Geophysical constraints on the structure and formation of Onepoto, Orakei, Pupuke and Tank Farm maar volcanoes, Auckland Volcanic Field
Published in New Zealand Journal of Geology and Geophysics, 2019
Alan G. Nunns, Manfred P. Hochstein
The Auckland Volcanic Field includes 53 basaltic volcanoes with similar geochemistry but with a variety of volcanic forms including scoria cones and lava flows, tuff rings, and maars (Searle 1964; Hayward et al. 2011; Lindsay et al. 2011). The Auckland Volcanic Field exemplifies a style of monogenetic volcanism in which individual volcanoes have small-scale magma fluxes and eruptive cycles of short duration (Németh and Kereszturi 2015; Smith and Németh 2017). Monogenetic volcanoes have a wide range of architectures depending on the interplay between magma type and supply and the geology, topography, and hydrology local to each volcano at the time of its eruption. Maar volcanoes have craters with original floors below the pre-eruptive surface, and typically surrounded by a pyroclastic rim (Lorenz 1973; White and Ross 2011).