Volcanic natural dams: identification,stability, and secondary effects |
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Authors: | Lucia Capra |
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Institution: | (1) Centro de Geociencias, UNAM, Campus Juriquilla, Queretaro, 76230, Mexico |
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Abstract: | Volcanic activity can enhance several secondary effects, including the formation of one or more natural dams. A common example
is from volcanic collapse, where huge mass volumes are rapidly emplaced, obstructing the drainage around a volcano. Their
duration depends on the volume of the obstructing mass, inflow rate, and on its textural characteristics. A block facies of
a debris avalanche produces durable and permeable dams that consist of decimeter to meter-sized blocks without matrix, whereas
a mixed facies is easily eroded after overflowing. Analysis of the sedimentological characteristics of different volcaniclastic
deposits that formed natural dams indicate that a mean grain size (Md) equal to −1 phi divides the field of debris avalanche
dams (Md < −1 phi) from that formed from other types of volcanic deposits. In addition, the matrix proportion of dams formed
by debris avalanches are less than the 50% and the percentage of mud fraction is highly variable, up to 30%. Combining the
granulometric textures with duration time of the dam shows no clear relation. Dam durability is probably more dependent on
the volume of the lake and the inflow rate. Only in some cases, as mud fraction increases is the blockage also less durable
because the lower permeability favors rapid infilling. The texture of the dam also determines the types of secondary flows
that originate by their breakdown. These vary from cohesive debris flow to hyperconcentrated flow, representing different
hazards due to their magnitude and their different behavior downstream. |
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Keywords: | Natural dam Volcano Volcanic collapse Debris flow |
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