How Polygenetic are Monogenetic Volcanoes: Case Studies of Some Complex Maar‐Diatreme Volcanoes

Abstract

The increasing number of field investigations and various controlled benchtop and largescale experiments have permitted the evaluation of a large number of processes involved in the formation of maar-diatreme volcanoes, the second most common type of smallvolume subaerial volcanoes on Earth. A maar-diatreme volcano is recognized by a volcanic crater that is cut into country rocks and surrounded by a low-height ejecta rim composed of pyroclastic deposits of few meters to up to 200 m thick above the syn-eruptive surface level. The craters vary from 0.1 km to up to 5 km wide and vary in depth from a few dozen meters to up to 300 m deep. Their irregular morphology reflects the simple or complex volcanic and cratering processes involved in their formation. The simplicity or complexity of the crater or the entire maar itself is usually observed in the stratigraphy of the surrounding ejecta rings. The latter are composed of sequences of successive alternating and contrastingly bedded phreatomagmatic-derived dilute pyroclastic density currents (PDC) and fallout depositions, with occasional interbedded Strombolian-derived spatter materials or scoria fall units, exemplifying the changes in the eruptive styles during the formation of the volcano. The entire stratigraphic sequence might be preserved as a single eruptive package (small or very thick) in which there is no stratigraphic gap or significant discordance indicative of a potential break during the eruption. A maar with a single eruptive deposit is quantified as monogenetic maar, meaning that it was formed by a single eruptive vent from which only a small and ephemeral magma erupted over a short period of time. The stratigraphy may also display several packages of deposits separated either by contrasting discordance surfaces or paleosoils, which reflect multiple phases or episodes of eruptions within the same maar. Such maars are characterized as complex polycyclic maars if the length of time between the eruptive events is relatively short (days to years). For greater length of time (thousands to millions of years), the complex maar will be quantified as polygenetic. These common depositional breaks interpreted as signs of temporal interruption of the eruptions for various timescales also indicate deep magma system processes; hence magmas of different types might erupt during the formation of both simple and complex maars. The feeding dikes can interact with groundwater and form closely distributed small craters. The latter can coalesce to form a final crater with various shapes depending on the distance between them. This observation indicates the significant role of the magmatic plumbing system on the formation and growth of complex and polygenetic maar-diatreme volcanoes.

Introductory Chapter: Updates in Volcanology - Transdisciplinary Nature of Volcano Science

“…In these models obviously the end-member types of volcanoes define short, small, simple (versus long-lasting, large and complex. Recent decade of research in addition, provided ample evidences that the scale of observation (hence the detail of information could be mined from volcanic systems) is important, and provides evidences to support that in real world end member type of monogenetic volcanoes are rare, and most of them shows some sort of complexity in a near continuous spectrum [20,[46][47][48][49][50][51][52]. This is more apparent when the magma that form those volcanic geoforms are more evolved [53,54].…”

“…Transdisciplinary approach within volcanology was always a key element of volcano science as volcanology addresses key questions over volcanic hazards, risk and resilience naturally moving along the interface of social science, humanities, natural science and non-academic (e.g. indigenous) knowledge [18][19][20][21][22][23][24][25]. Especially in recent years more and more researches were conducted on subjects to help to understand the interface between western science and traditional knowledge [26][27][28][29][30].…”

Diversity of Volcanic Geoheritage in the Canary Islands, Spain

“…Sometimes, mixed monogenetic volcanoes are found, where hydromagmatic and phreatomagmatic phases at the beginning of the formation of the volcano and later magmatic phases are identified [62,63]. Special mention should be made of the aligned geyser vents in the crater of the Tinguaton historical eruption on Lanzarote [45].…”

Features That Favor the Prediction of the Emplacement Location of Maar Volcanoes: A Case Study in the Central Andes, Northern Chile

“…The small-volume scale of monogenetic volcanoes enables preservation of the petrological features of the magmatic systems [13]. Juvenile material of monogenetic volcanoes is considered a "window to the mantle" allowing an insight into the processes that produce their magmas, (e.g., [105][106][107][108][109][110]), whereas the lithic content of these monogenetic systems could be considered as a "window to the crust and to the substrate" (e.g., [111][112][113][114][115]). In both senses, monogenetic volcanoes provide a unique opportunity to study the details of volcanic processes from the magmatic source to the surface.…”