**2. Geological setting**

The geology of Lanzarote is characterized by the existence of old Miocene massifs located to the North and South of the island and by a Quaternary fissurealigned volcanic field in the central part, in which vast volcanic fields cover discordantly the underlying Mio-Pliocene materials (**Figure 1**). Most of the eruptive centers are small monogenetic edifices arranged in several alignments trending NE– SW and ENE-WSW roughly parallel to each other, and dispersed over the territory ([15] and references therein).

Two historical eruptions took place in the central volcanic field of the island: the 1730–36 Timanfaya eruption and the 1824 eruption [16]. Both were multiple-fissure type eruptions but quite different in magnitude [17]. While in 1824 the eruption lasted nearly three months and only three small fissures (less than 500 m in length) where opened, the Timanfaya eruption lasted nearly 6 years and formed hundreds of vents aligned along a 13 km eruptive fissure, from where lava flows that covered one-third of the island were issued [9, 11, 17–21]. Thus, Timanfaya constitutes the highest magnitude eruptive process occurred in historical times in Lanzarote and the Canary Islands.

Mazo volcano is located in the central volcanic field, to the North of the eastern end of the main eruptive fissure of Timanfaya (**Figure 1**). It is a basanitic elongated

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**Figure 1.**

*PP: Pico Partido.*

*Syn-Eruptive Lateral Collapse of Monogenetic Volcanoes: The Case of Mazo Volcano…*

scoria cone trending ENE-WSW [18]. This scoria cone and the related deposits are

*Location of Lanzarote Island and map of quaternary volcanic deposits of the central volcanic field of Lanzarote showing the location of Mazo volcano and the eruptive fissures of Timanfaya (dash black lines). White dashed square shows the location of Figure 2. CC: Caldera de los Cuervos; CR: Caldera de La Rilla;* 

Mazo is a monogenetic volcano with a relative height of 179 m, resting on a leaning

volcanic substrate with a difference in height of 30 m between the highest and the lowest point of its external base. The cone and deposits are partially covered by lavas from historical eruptions, leaving exposed only the highest parts of Mazo deposits. The cone has an irregular shape and a crater with two open depressions aligned in the ENE-WSW direction, with a maximum diameter of 493 m. The main crater, located to the SW, has a funnel shape, 178 m deep inside, with an internal platform on its northern slope elevated 18 m over the bottom (**Figure 2**). The other depression is of bowl type, with an interior depth of 120 m. The rim of this double depression is higher in its southern part (429 m asl), just at the contact between both depressions. From this point, the rim appears lobed towards the NE and SW, gradually decreasing

in altitude until reaching a minimum height of 280 m in its NW sector.

partially overlaid by historical lava flows.

**3. Geological analysis of Mazo volcano and deposits**

*DOI: http://dx.doi.org/10.5772/intechopen.93882*

*Syn-Eruptive Lateral Collapse of Monogenetic Volcanoes: The Case of Mazo Volcano… DOI: http://dx.doi.org/10.5772/intechopen.93882*

**Figure 1.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

understanding of hazards in monogenetic volcanic fields.

The geology of Lanzarote is characterized by the existence of old Miocene massifs located to the North and South of the island and by a Quaternary fissurealigned volcanic field in the central part, in which vast volcanic fields cover discordantly the underlying Mio-Pliocene materials (**Figure 1**). Most of the eruptive centers are small monogenetic edifices arranged in several alignments trending NE– SW and ENE-WSW roughly parallel to each other, and dispersed over the territory

Two historical eruptions took place in the central volcanic field of the island: the 1730–36 Timanfaya eruption and the 1824 eruption [16]. Both were multiple-fissure type eruptions but quite different in magnitude [17]. While in 1824 the eruption lasted nearly three months and only three small fissures (less than 500 m in length) where opened, the Timanfaya eruption lasted nearly 6 years and formed hundreds of vents aligned along a 13 km eruptive fissure, from where lava flows that covered one-third of the island were issued [9, 11, 17–21]. Thus, Timanfaya constitutes the highest magnitude eruptive process occurred in historical times in Lanzarote and

Mazo volcano is located in the central volcanic field, to the North of the eastern end of the main eruptive fissure of Timanfaya (**Figure 1**). It is a basanitic elongated

**2. Geological setting**

([15] and references therein).

the Canary Islands.

catastrophic events in the evolution of polygenetic volcanic structures. Factors inducing or triggering volcanic flank collapses include the violence of the eruption, high eruptive rates, hydrothermal alteration, existence of relatively steep slopes, presence and reactivation of faults, magma intrusion, high saturation of volcanic rocks in water, presence of lava plugs during the active period, structural heterogeneities and geotechnical differences between volcanic edifices and their basement, seismicity, caldera collapse or even climatic fluctuations ([2] and reference therein). In contrast, instability processes in monogenetic volcanoes have been much less documented and have often received less attention given its less volume and less potential hazard (eg. [6–11]). Nevertheless, it should be taken into account that mafic monogenetic volcanic systems are the most frequent and widespread magmatism on Earth, usually located very close to population centers [7]. The most documented instability process in monogenetic cones are those related to the partial collapse and passive transport of fragments of the edifice during the emission of lava flows, process known as rafting (eg. [6–11]). The clearest evidence of rafting processes in monogenetic edifices is the existence of huge blocks on the surface of lava flows composed of agglutinated materials coming from the cone [12]. Rafting has been related to lava flows and sill emplacement at the base of the cone, changes in eruptive style or the existence of previous cones or topographical constrains ([13] and reference therein). Although flank collapses forming VDA with liquified non-turbulent granular flows are usually linked to stratovolcanoes [14] and rafting processes are the common result of instability in monogenetic cones, in this work we demonstrate VDA also happen in small volcanic cones, such as in the historical volcanic cone of Mazo (Lanzarote, Canary Islands). Here, we present the first detailed description of a syn-eruptive volcanic flank collapse in a monogenetic volcanic cone and describe the associated debris avalanche and blast deposits; as well as the conditioning and triggering factors of the collapse, and the implications for the volcanic eruption development. The finding of this volcanic flank collapse during a mafic fissure eruption has local implications in the interpretation, timing and reconstruction of the Timanfaya eruption and global implications in the

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*Location of Lanzarote Island and map of quaternary volcanic deposits of the central volcanic field of Lanzarote showing the location of Mazo volcano and the eruptive fissures of Timanfaya (dash black lines). White dashed square shows the location of Figure 2. CC: Caldera de los Cuervos; CR: Caldera de La Rilla; PP: Pico Partido.*

scoria cone trending ENE-WSW [18]. This scoria cone and the related deposits are partially overlaid by historical lava flows.
