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Armin Freundt Wilfried Strauch Steffen Kutterolf Hans-Ulrich Schmincke 《Pure and Applied Geophysics》2007,164(2-3):527-545
This paper emphasizes the fact that tsunamis can occur in continental lakes and focuses on tsunami triggering by processes
related to volcanic eruptions and instability of volcanic edifices. The two large lakes of Nicaragua, Lake Managua and Lake
Nicaragua, host a section of the Central American Volcanic Arc including several active volcanoes. One case of a tsunami in
Lake Managua triggered by an explosive volcanic eruption is documented in the geologic record. However, a number of events
occurred in the past at both lakes which were probably tsunamigenic. These include massive intrusion of pyroclastic flows
from Apoyo volcano as well as of flank-collapse avalanches from Mombacho volcano into Lake Nicaragua. Maar-forming phreatomagmatic
eruptions, which repeatedly occurred in Lake Managua, are highly explosive phenomena able to create hugh water waves as was
observed elsewhere. The shallow water depth of the Nicaraguan lakes is discussed as the major limiting factor of tsunami amplitude
and propagation speed. The very low-profile shores facilitate substantial in-land flooding even of relatively small waves.
Implications for conceiving a possible warning system are also discussed. 相似文献
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We distinguish three eruptive units of pyroclastic flows (T1, T2, and T3; T for trass) within the late Quaternary Laacher See tephra sequence. These units differ in the chemical/mineralogical composition of the essential pyroclasts ranging from highly differentiated phonolite in T1 to mafic phonolite in T3. T1 and T2 flows were generated during Plinian phases, and T3 flows during a late Vulcanian phase. The volume of the pyroclastic flow deposits is about 0.6 km3. The lateral extent of the flows from the source vent decreases from > 10 km (T1) to < 4.5 km (T3). In the narrow valleys north of Laacher See, the total thickness of the deposits exceeds 60 m.At least 19 flow units in T1, 6 in T2, and 4 in T3 can be recognized at individual localities. Depositional cycles of 2 to 5 flow units are distinguished in the eruptive units. Thickness and internal structure of the flow units are strongly controlled by topography. Subfacies within flow units such as strongly enriched pumice and lithic concentration zones, dust layers, lapilli pipes, ground layers, and lithic breccias are all compositionally related to each other by enrichment or depletion of clasts depending on their size and density in a fluidized flow. While critical diameters of coarse-tail grading were found to mark the boundary between the coarse nonfluidized and the finer fluidized grain-size subpopulations, we document the second boundary between the fluidized and the very fine entrained subpopulations by histograms and Rosin-Rammler graphs. Grain-size distribution and composition of the fluidized middle-size subpopulations remained largely unchanged during transport.Rheological properties of the pyroclastic flows are deduced from the variations in flow-unit structure within the valleys. T1 flows are thought to have decelerated from 25 m/s at 4 km to < 15 m/s at 7 km from the vent; flow density was probably 600–900 kg/m3, and viscosity 5–50 P. The estimated yield strength of the flows of 200– > 1000 N/m2 is consistent with the divergence of lithic size/distance curves from purely Newtonian models; the transport of lithics must be treated as in a Bingham fluid. The flow temperature probably decreased from T1 (300°–500°C) to T3 (<200°C).A large-scale longitudinal variation in the flow units from proximal through medial to distal facies dominantly reflects temporal changes during the progressive collapse of an eruption column. Only a small amount of fallout tephra was generated in the T1 phase of eruption. The pyroclastic flows probably formed from relatively low ash fountains rather than from high Plinian eruption columns. 相似文献
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A multidisciplinary analysis of intraplate volcanic complexes interbedded with shallow and deeper marine sediments of a Late Miocene carbonate platform (Iblean Plateau, Sicily) has allowed a detailed paleo-environmental reconstruction. Our approach includes sedimentology, physical volcanology, stratigraphy, geochemistry/mineralogy, paleontology and 40Ar/39Ar dating. Four volcanic complexes are distinguished from each other. Two comprise an eastern shallow water platform (diatreme field and Carlentini complex) and two a western deeper water environment representing a seamount belt on the carbonate ramp (Valle Guffari seamount and Mineo complex). The late Miocene volcanism was not time-equivalent: episodic eruptions took place from the Late Tortonian (ca. 9.38 Ma at Mt. Carrubba) to Early Messinian (ca. 6.46 Ma at Valle Guffari). Explosive volcanism of the diatreme field may be related geodynamically to the period of periodic sea-level oscillations at the onset of the Messinian Salinity Crisis. Marine diatomites preserved in the crater areas of two diatremes are the only remnants of Early Messinian diatomites in the eastern Iblean Mountains. 相似文献
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