Between the years of 30 b.c. to a.d. 80, during the Late Formative period, the site of Izapa was flooded by lahars associated with an explosive eruption of the San Antonio volcano (part of the Tacaná Volcanic Complex). Computer simulations suggest that hot pyroclastic flows did not impact Izapa directly, but did impact the region considerably, filling and clogging the Cahuacan and Mixcun rivers with hot debris. The material was quickly saturated by heavy rains and, as the water from the rivers overtopped the obstruction, remobilized in the form of a hot mixture of mud and water known as a lahar (or flood of volcanic origin), which flowed down through the piedmont zone along the Cahuacan, Mixcun-Suchiate, and Izapa rivers. At Izapa, the flood took the form of a 6-m catastrophic wave of mud and water that likely destroyed crops and caused many causalities, surrounding the architectural mounds at Izapa with a muddy landscape. The floods also dramatically affected the rivers downstream, undoubtedly wreaking serious damage to the transport and trade of goods along the coast.

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A new geological map at 1:50,000 scale of La Reforma Caldera Complex has been produced applying modern survey methodologies to volcanic areas. This map aims to represent a reliable and objective tool to understand the geological evolution of the region. La Reforma Caldera Complex is a Pleistocene nested caldera located in the central part of the Baja California peninsula, Mexico. The twelve formations defined within the Quaternary volcanic record were grouped into three phases (pre-caldera, caldera, and post-caldera). The pre-caldera phase (>1.35 Ma) is characterized by scattered eruptions, mostly occurred in submarine environment. The caldera phase (1.35-0.96 Ma) groups several distinct explosive and effusive eruptions that formed the present-day caldera depression. The post caldera phase includes scattered effusive eruptions (ended at 0.28 Ma) and resurgence, characterized by several hundred meters of uplift of the central block within the caldera depression.

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We present a new 1:80,000-scale geologic map of the Acoculco caldera (Ac) located between the states of Puebla and Hidalgo in eastern México. The map, encompassing an area of 856 km 2 , is grounded on an ArcMap data set and is supported by nine new 40 Ar/ 39 Ar dates. The caldera lies upon Cretaceous limestones and Miocene to Pliocene volcanic rocks (13-3 Ma). The caldera consists of 31 lithostatrigraphic units formed between 2.7 and 0.06 Ma that include a wide variety of volcanic landforms (cinder cones, lava domes). The caldera has a semi-circular shape (18-16 km) bounded by the Atotonilco scarp to the north, the NW-SE Manzanito fault to the west, and scattered vents to the east and southern parts. The distribution of the Acoculco ignimbrite, the lithic breccia, and lacustrine sediments define the caldera ring fault. Late Pleistocene activity and pervasive hydrothermal alteration suggest a high geothermal potential in the area.

Abstract. On 27 May 1937, after one week of sustained heavy rainfall, a voluminous flood caused the death of at least 300 people and the destruction of the historic El Carmen church and several neighborhoods in the mining region of Tlalpujahua, Michoacán, central Mexico. This destructive flood was triggered by the breaching of the impoundment of the Los Cedros tailings and the sudden release of circa 16 Mt of water-saturated waste materials. The muddy silty flood, moving at estimated speeds of 20-25 m s −1 , was channelized along the Dos Estrellas and Tlalpujahua drainages and devastated everything along its flow path. After advancing 2.5 km downstream, the flood slammed into El Carmen church and surrounding houses at estimated speeds of ∼ 7 m s −1 , destroying many construction walls and covering the church floor with ∼ 2 m of mud and debris. Revision of eyewitness accounts and newspaper articles, together with analysis of archived photographic materials, indicated that the flood consisted of three muddy pulses. Stratigraphic relations and granulometric data for selected proximal and distal samples show that the flood behaved as a hyperconcentrated flow along most of its trajectory. A total volume of the Lamas flood deposit was estimated as 1.5 × 10 6 m 3 . The physically based bidimensional (2-D) hydraulic model FLO-2D was implemented to reproduce the breached flow (0.5 sediment concentration) with a maximum flow discharge of 8000 m 3 s −1 for a total outflow volume (sediment + water) of 2.5 × 10 6 m 3 , similar to the calculations obtained using field measurements.Even though premonitory signs of possible impoundment failure were reported days before the flood, and people living downstream were alerted, authorities ordered no evacuations or other mitigative actions. The catastrophic flood at Tlalpujahua provides a well-documented, though tragic, example of impoundment breaching of a tailings dam caused by the combined effects of intense rainfall, dam weakness, and inadequate emergency-management protocols -unfortunately an all-too-common case scenario for most of the world's mining regions.

The Joya Honda maar (JHm) is located in central Mexico, 35 km NNE of the city of San Luis Potosí. It lies in the Plio-Quaternary alkaline Ventura-Espíritu Santo Volcanic Field located in the eastern part of Mesa Central province. The JHm eruption occurred at 311±19 ka (40Ar/39Ar) along a fissure that formed an elliptical crater (c. 1.3×0.9 km wide and c. 270 m deep) with a major axis oriented to the ENE–WSW. The eruption generated pyroclastic surge deposits that preferentially extended up to a distance of 7 km to the NW–NE of the crater, with a very limited distribution to the south. At the crater rim, the sequence is 60–80 m thick on the NE–NW wall and 1–15 m thick on the south–SW rim. The JHm sequence is divided into five units with different structures, textures, granulometry and components. The juvenile basanite clasts of these units display differences in vesicularity, density and morphology under scanning electron microscopy. These units correspond to the same number of eruptive phases as follows: Phase 1 occurred as a series of alternating strombolian and phreatomagmatic explosions that dispersed fall deposits and base surges; Phase 2 began with strombolian activity that emplaced basanite scoria with low contents of mantle xenoliths; Phase 3 continued with phreatomagmatic explosions that emplaced wet and dry pyroclastic surges; Phase 4 generated strombolian explosions rich in mantle xenoliths; and Phase 5 produced a violent strombolian phase that dispersed fallouts rich in mantle xenoliths and intermixed with discrete phreatomagmatic explosions that emplaced pyroclastic surges. These eruptive fluctuations during the genesis of JHm are a response to the relative proportions of magma–water interaction through time and complex faulting of the calcareous rocks underneath the volcano. The distribution and textural characteristics of the deposits suggest that simultaneous or alternating vents were active during the eruption, possibly following a fissure. These variations may have been subordinated to factors such as the availability of groundwater, the velocity of magma ascent, the discharge rate and degassing.