The cohesive Naranjo debris-flow deposit (10 km 3):
Mass movement processes on volcanic terrains such as landslides and debris avalanches can cause the obstruction of main drainages producing the formation of temporary dams. A good example of this occurred 18.5 ka ago when the eastern flank of the Nevado de Colima Volcano collapsed producing a debris-avalanche deposit that was previously described as one of the largest in the world. The deposit extended from the volcanic summit as far as the Pacific coast, 120 km away. New stratigraphic, sedimentological, and componentry data suggest that the volcanic collapse of Nevado de Colima resulted in a debris avalanche that traveled 20 km southeast to the Naranjo River. There it crashed against a topographic barrier consisting of Cretaceous limestones (Cerro la Carbonera) and the flow direction was diverted to the south down the Naranjo River channel for another 25 km before the avalanche came to a halt. The obstruction of the drainage produced a temporary dam that stored ca. 1 km3 of water and deposited fluvial and slack-water sediments. Some time after the damming, the accumulated water-sediment load was able to overtop the obstructing material and to release a breakout flow with a calculated initial flow discharge of 3.5 million m3/s. The resulting flood (cohesive debris flow) followed the channel of the Naranjo River and, due to the high erodibility of the channel and introduction of substrate material, the debris flow progressively increased its volume up to 10 km3, six times its initial volume. This study highlights the relevance of evaluating the potential remobilization of debris-avalanche deposits to initiate large magnitude cohesive debris flows. Therefore, the hazard and risk analysis of future potential events of this nature must consider the pre-eruption conditions and the topography surrounding a volcano. 7 2002 Elsevier Science B.V. All rights reserved.
Giant debris avalanches from the Colima Volcanic Complex, Mexico: Implications for long-runout landslides (>100 km) and hazard assessment
At least two giant volcanic debris-avalanche deposits are associated with the Colima Volcanic Complex located in the western part of the Trans-Mexican volcanic belt. One avalanche originated from Volcan de Colima (3820 m), probably 4300 yr ago. A much larger avalanche originated from Nevado de Colima (4240 m) 18500 yr ago; it traveled more than 120 km from its source and covered an area of at least 2200 km 2 , almost twice the area of any previously described avalanche deposit. This older debris avalanche is the second largest (by volume) known, has the longest travel distance yet reported, and has one of the lowest height/length ratios (0.04). The avalanche material was probably hot during emplacement and, after initial slope failure, may have behaved similarly to a pyroclastic flow. Such large long-runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard that must be considered in risk assessment.
Ultrastructural observations of the spermiogenesis in the Parotoplaninae (Plathelminthes, Proseriata) with special reference to a striated appendage of the intercentriolar body
SummaryThe spermiogenesis of three species of the Parotoplaninae (Otoplanidae, Proseriata) is described based on electron-microscopical observations. Special reference is given to organelles which do not persist in mature male gametes. One of these organelles is a striated appendage of the intercentriolar body. This differentiation has not been reported from any other plathelminth taxa up to now. The striated appendage, which may serve as a strengthening element, is hypothesized to be an autapomorphic feature of the Parotoplaninae.