Bernd Zimanowski - Academia.edu (original) (raw)
Papers by Bernd Zimanowski
One of the still open question in volcano-seismology concerns the quantitative de- scription of t... more One of the still open question in volcano-seismology concerns the quantitative de- scription of the seismic radiation caused during volcanic explosions. Many models have been proposed in the past, but it was not possible yet to find a standard de- scription similar to the double couple in earthquake seismology. Trying to solve this problem, the number of parameters that influence
Physical Review E, 1998
We propose a phenomenological model for explosive water-melt interactions. Thermohydraulic fractu... more We propose a phenomenological model for explosive water-melt interactions. Thermohydraulic fracturing was experimentally identified to be the main contributor to explosive energy release. We found experimental evidence that the model is applicable for a variety of melt compositions with very different thermal and rheological properties. The proposed mechanism does not require special premixing conditions. The pre-explosive geometries yielding the most
Experiments in volcano-ice interaction were carried out to explain and quantify processes of heat... more Experiments in volcano-ice interaction were carried out to explain and quantify processes of heat transfer from magma to water and ice in phreatomagmatic and subglacial eruptions. Special emphasis was placed on laboratory experiments using re-melted rocks and ice. Settings studied so far are: (1) lava-ice contact where magma or hot rocks and ice have a common interface in a semi-static setting, a very common occurrence when lavas flow adjacent to ice, and (2) hot jets of steam or water impacting on ice, a useful analogue to energetic geothermal upwelling or fully subglacial volcanic eruptions. For the lava ice contact a setup was built at the Volcanological Laboratory at the University of Würzburg where volcanic rock are heated up and melted for experiments. Experiments included pouring of melt over ice and by placing a block of ice on top of a batch of magma. Melting rates and temperatures at various parts of the system were measured as a function of time. At the University of Icel...
Bulletin of Volcanology, 2014
The source conditions of volcanic plumes and collapsing fountains are investigated by means of la... more The source conditions of volcanic plumes and collapsing fountains are investigated by means of large-scale experiments. In the experiments, gas-particle jets issuing from a cylindrical conduit are forced into the atmosphere at different mass flow rates. Dense jets (high particle volumetric concentration, e.g., C 0 >0.01) generate collapsing fountains, whose height scales with the squared exit velocity. This is consistent with Bernoulli's equation, which is a good approximation if air entrainment is negligible. In this case, kinetic energy is transformed into potential energy without any significant loss by friction with the atmosphere. The dense collapsing fountain, on hitting the ground, generates an intense shear flow similar to a pyroclastic density current. Dilute hot jets (low particle volumetric concentration, e.g., C 0 <0.01) dissipate their initial kinetic energy at much smaller heights than those predicted by Bernoulli's equation. This is an indication that part of the total mechanical energy is lost by friction with the atmosphere. Significant air entrainment results in this case, leading to the formation of a buoyant column (plume) from which particles settle similarly to pyroclastic fallout. The direct measurement of entrainment coefficient in the experiments suggests that dense collapsing fountains form only when air entrainment is not significant. This is a consequence of the large density difference between the jet and the atmosphere. Cold dilute experiments result in an entrainment coefficient of about 0.06, which is typical of pure jets of fluid dynamics. Hot dilute experiments result in an entrainment coefficient of about 0.11, which is typical of thermally buoyant plumes. The entrainment coefficients obtained by experiments were used as input data in numerical simulations of fountains and plumes. A numerical model was used to solve the classic top-hat system of governing equations, which averages the field variables (e.g., column velocity and density) across the column. The maximum heights calculated with the model agree well with those observed experimentally, showing that our entrainment coefficients are compatible with a top-hat model. Dimensional analysis of the experimental data shows that a value of 3 for the source densimetric Froude number characterizes the transition between dense collapsing fountains and dilute plumes. This value delimits the source conditions (exit velocity, conduit radius, and particle volumetric concentration) for pyroclastic flow (<3) and fallout (>3).
Pyroclastic flows are ground hugging, hot, gas-particle flows. They represent the most hazardous ... more Pyroclastic flows are ground hugging, hot, gas-particle flows. They represent the most hazardous events of explosive volcanism, one striking example being the famous historical eruption of Pompeii (AD 79) at Vesuvius. Much of our knowledge on the mechanics of pyroclastic flows comes from theoretical models and numerical simulations. Valuable data are also stored in the geological record of past eruptions,
Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatrem... more Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in
High Temperatures-High Pressures, 2002
ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough... more ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough knowledge of its thermophysical properties. Therefore, thermal conductivity, specific heat, and viscosity of volcanic rock material were determined in a wide temperature range. Especially, the properties of the molten material were investigated in detail. The material was taken from the Pietre-Cotte lava flow located on the isle of Vulcano, north of Sicily. The thermal conductivity of the material was determined in the temperature range 293 - 1623 K by the hot-wire method. Melting occurs above HOOK The specific heat was measured by differential scanning calorimetry between 347 and 1671 K. The viscosity of the lava melt was determined with a rotational viscometer HAAKE M5. The viscometer was enclosed in a high-temperature furnace optimised for the temperature range 1373 - 1598 K.
Eos, Transactions American Geophysical Union, 2007
Nuclear Engineering and Design, 1995
An experimental set-up for the generation of mixtures of silicate melt (remotten volcanic rocks) ... more An experimental set-up for the generation of mixtures of silicate melt (remotten volcanic rocks) and water and the triggering of steam explosions was built at the Institut fur Kemenergetik (IKE) at Stuttgart. The temperature of melts investigated ranged from 1200 to 1600 °C. The chosen experimental configuration resulted in mixtures of 0.5-20 ml of water in 125 ml of melt, the water dispersed into droplets that were entrapped by domains of melt. More than 300 experimental runs were performed using a variety of remolten volcanic rocks. Explosive premixtures were triggered by shock waves of less than 8 J kinetic energy. Only part of the melt and part of the water of the mixture reacted thermally, thus causing an explosion. The most intensive explosions were produced by reaction of about 3 ml of water and 6 ml of melt and released kinetic energy of more than 600 J. Higher melt viscosity resulted in weaker explosions. Higher mixing energy enhanced probability and intensity of explosions. Melt temperatures were only of minor influence. If bubbles of non-condensible gases were abundant in a mixture of otherwise explosive water/melt ratio, explosions could not be triggered.
Nature, 1999
... We find that surface features of ash grains can be used to identify the dynamic contact of ma... more ... We find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water. ... Deadline: Jun 18 2011; Reward: Varies. Material supply of non-commercial compounds matching the shown core structure is desired. The Seek ...
Journal of Volcanology and Geothermal Research, 2007
Molten-Fuel-Coolant Interaction (MFCI) experiments were performed using remelted foiditic rock sa... more Molten-Fuel-Coolant Interaction (MFCI) experiments were performed using remelted foiditic rock samples from the West Eifel volcanic field (Germany). Two experimental series were carried out with one magmatic melt and two water compositions. Bidistilled water was used in the first series (DW-1 to DW-5). In the second series (SW-1 to SW-5), the bi-distilled water was saturated (350 g L − 1 ) with sodium chloride (NaCl). For both experimental series the fragmentation history and the energy release were recorded and compared. The smallest particles (≤125 μm) were studied using scanning electron microscopy (SEM). Most MFCI experiments with bi-distilled water reached higher explosion intensities than the experiments with the saline water. This was accompanied by higher particle ejection velocities as well as the formation of more fine-grained and more interactive particles of angular shape. Additionally, the smallest artificial pyroclasts were examined by evolved gas analyses (EGA). The particles from the MFCI experiments with salt solutions are found to contain more sodium hydroxide (NaOH). These observations can be explained by thermodynamic arguments. In contrast to the MFCI experiments with pure water, an additional reaction occurs with saline water that results in evolution of hydrogen chloride (HCl) gas and leaves a residue of sodium hydroxide. The MFCI process with saline water consumes more enthalpy and Gibbs free energy, so that less energy is available for the explosion. With other sodium halides dissolved in the water (NaF, NaBr or NaI) the additional reaction can be predicted to have greater or lesser effects on phreatomagmatic explosions.
Journal of Volcanology and Geothermal Research, 2011
A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic... more A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic rocks using wide gap viscometry. The complex composition of magmatic melts leads to complicated rheologic behavior which cannot be described with one simple model. Therefore, measurement procedures which are able to quantify non-Newtonian behavior have to be employed. Furthermore, the experimental apparatus must be able to deal with inhomogeneities of magmatic melts. We measured the viscosity of a set of materials representing a broad range of volcanic processes. For the lower viscous melts (low-silica compositions), non-Newtonian behavior is observed, whereas the high-silica melts show Newtonian behavior in the measured temperature and shear rate range (T = 1423 K − 1623 K, γ̇=10 − 2 s − 1 − 20 s − 1 ). The non-Newtonian materials show power-law behavior. The measured viscosities η and power-law indexes m lie in the intervals 8 Pa s ≤ η ≤ 210 3 Pa s, 0.71 ≤ m ≤ 1.0 (Grímsvötn basalt), 0.9 Pa s ≤ η ≤ 350 Pa s, 0.61 ≤ m ≤ 0.93 (Hohenstoffeln olivine-melilitite), and 8 Pa s ≤ η ≤ 1.510 4 Pa s, 0.55 ≤ m ≤ 1.0 (Sommata basalt). Measured viscosities of the Newtonian high-silica melts lie in the range 10 4 Pa s ≤ η ≤ 310 5 Pa s.
Journal of Volcanology and Geothermal Research, 2008
Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, the... more Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material,
Journal of Volcanology and Geothermal Research, 2002
In addition to large amounts of fragmented country rocks, maar^diatreme volcanoes commonly eject ... more In addition to large amounts of fragmented country rocks, maar^diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and/or xenocrysts derived from the country rocks surrounding the diatremes. Formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences. The thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks. Vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks. Surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass-flow deposit subsequent to each explosion. When, prior to a new explosion, magma rises from the underlying feeder dyke into the root zone, it intrudes this clastic debris, inflates it and may mingle with the debris to form a peperite. Subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains, juvenile lapilli and bombs containing xenoliths or xenocrysts from the country-rock debris. Lack of further explosions, but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs. ß
Journal of Volcanology and Geothermal Research, 2002
Hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key... more Hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites. Experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process. These studies show that for a wide range of shear rates a laminar flow behaviour of the system magma^liquefied sediment can be expected, i.e. turbulent mingling is not a realistic scenario. Formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities. In addition to the hydrodynamics, cooling processes must also be considered during peperite formation. Calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time. The consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable. However, as smaller domain sizes (peperitic grain sizes) exist in nature, we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes. ß 2002 Published by Elsevier Science B.V.
Journal of Volcanology and Geothermal Research, 1998
Journal of Volcanology and Geothermal Research, 1998
Detailed field investigations of kimberlite pipes of the Upper Cretaceous Gibeon Kimberlite Field... more Detailed field investigations of kimberlite pipes of the Upper Cretaceous Gibeon Kimberlite Field in southern Namibia revealed geologic features which do neither agree with extensive nor with explosive vesiculation. In the pipe Hanaus 2, vesicle-free magmatic kimberlite intruded the diatreme as a plug. Here we report on the first experiments in which phreatomagmatic explosions were produced with remolten natural, non-fragmental magmatic kimberlite from the Hanaus 2 central plug as a best fit model kimberlite magma system. After water was injected into the melt under controlled conditions, Ž . the resulting water-melt mix was triggered by a low-energy shock wave -1 J and a violent explosion was obtained: High-energy shock waves of several 1000 J were generated and pyroclasts were ejected with a maximum speed ) 400 mrs. q 1998 Elsevier Science B.V.
Journal of Geophysical Research, 2006
The release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard a... more The release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard assessment and civil defense. The explosive production of volcanic ash by intensive fragmentation of magma and host rocks represents a substantial part of this energy. For cases of explosive eruption where predominantly host rock was fragmented (phreatomagmatic eruptions) to form the major part of volcanic
Journal of Geophysical Research, 2008
... Adapted from Siebe et al. [1993] and Siebert and Carrasco-Nún˜ez [2002]. B11201 AUSTIN-ERICKS... more ... Adapted from Siebe et al. [1993] and Siebert and Carrasco-Nún˜ez [2002]. B11201 AUSTIN-ERICKSON ET AL.: PHREATOMAGMATIC EXPLOSIONS OF RHYOLITE 3 of 12 B11201 Page 4. ... al., 2003; Rust et al., 2004; Castro et al., 2005; Gonnermann and Manga, 2005]. ...
Journal of Geophysical Research, 2007
1] A newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindr... more 1] A newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products (tephra). Blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas. Opening of fast solenoid valves results in impulse-like coupling of the released gas to the sample. The system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition. Depending on the specific mechanical energy (SME) of the system, which results from DPV/m, where DP is gas overpressure (i.e., pressure > atmospheric), V is gas volume, and m is sample mass, different behaviors are observed. If SME > 2.6 kJ/kg, a dilute plume develops, and particles are sedimented by fallout exclusively. If SME < 1.5 kJ/kg, the exiting column collapses and develops a shear current similar to a pyroclastic flow. The Reynolds number of the shear currents is >10 6 , implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments. The measured shear current velocities are proportional to the impact mass flow rate, i.e., the product of mixture density and impact velocity. Experimental data and grain-size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows.
One of the still open question in volcano-seismology concerns the quantitative de- scription of t... more One of the still open question in volcano-seismology concerns the quantitative de- scription of the seismic radiation caused during volcanic explosions. Many models have been proposed in the past, but it was not possible yet to find a standard de- scription similar to the double couple in earthquake seismology. Trying to solve this problem, the number of parameters that influence
Physical Review E, 1998
We propose a phenomenological model for explosive water-melt interactions. Thermohydraulic fractu... more We propose a phenomenological model for explosive water-melt interactions. Thermohydraulic fracturing was experimentally identified to be the main contributor to explosive energy release. We found experimental evidence that the model is applicable for a variety of melt compositions with very different thermal and rheological properties. The proposed mechanism does not require special premixing conditions. The pre-explosive geometries yielding the most
Experiments in volcano-ice interaction were carried out to explain and quantify processes of heat... more Experiments in volcano-ice interaction were carried out to explain and quantify processes of heat transfer from magma to water and ice in phreatomagmatic and subglacial eruptions. Special emphasis was placed on laboratory experiments using re-melted rocks and ice. Settings studied so far are: (1) lava-ice contact where magma or hot rocks and ice have a common interface in a semi-static setting, a very common occurrence when lavas flow adjacent to ice, and (2) hot jets of steam or water impacting on ice, a useful analogue to energetic geothermal upwelling or fully subglacial volcanic eruptions. For the lava ice contact a setup was built at the Volcanological Laboratory at the University of Würzburg where volcanic rock are heated up and melted for experiments. Experiments included pouring of melt over ice and by placing a block of ice on top of a batch of magma. Melting rates and temperatures at various parts of the system were measured as a function of time. At the University of Icel...
Bulletin of Volcanology, 2014
The source conditions of volcanic plumes and collapsing fountains are investigated by means of la... more The source conditions of volcanic plumes and collapsing fountains are investigated by means of large-scale experiments. In the experiments, gas-particle jets issuing from a cylindrical conduit are forced into the atmosphere at different mass flow rates. Dense jets (high particle volumetric concentration, e.g., C 0 >0.01) generate collapsing fountains, whose height scales with the squared exit velocity. This is consistent with Bernoulli's equation, which is a good approximation if air entrainment is negligible. In this case, kinetic energy is transformed into potential energy without any significant loss by friction with the atmosphere. The dense collapsing fountain, on hitting the ground, generates an intense shear flow similar to a pyroclastic density current. Dilute hot jets (low particle volumetric concentration, e.g., C 0 <0.01) dissipate their initial kinetic energy at much smaller heights than those predicted by Bernoulli's equation. This is an indication that part of the total mechanical energy is lost by friction with the atmosphere. Significant air entrainment results in this case, leading to the formation of a buoyant column (plume) from which particles settle similarly to pyroclastic fallout. The direct measurement of entrainment coefficient in the experiments suggests that dense collapsing fountains form only when air entrainment is not significant. This is a consequence of the large density difference between the jet and the atmosphere. Cold dilute experiments result in an entrainment coefficient of about 0.06, which is typical of pure jets of fluid dynamics. Hot dilute experiments result in an entrainment coefficient of about 0.11, which is typical of thermally buoyant plumes. The entrainment coefficients obtained by experiments were used as input data in numerical simulations of fountains and plumes. A numerical model was used to solve the classic top-hat system of governing equations, which averages the field variables (e.g., column velocity and density) across the column. The maximum heights calculated with the model agree well with those observed experimentally, showing that our entrainment coefficients are compatible with a top-hat model. Dimensional analysis of the experimental data shows that a value of 3 for the source densimetric Froude number characterizes the transition between dense collapsing fountains and dilute plumes. This value delimits the source conditions (exit velocity, conduit radius, and particle volumetric concentration) for pyroclastic flow (<3) and fallout (>3).
Pyroclastic flows are ground hugging, hot, gas-particle flows. They represent the most hazardous ... more Pyroclastic flows are ground hugging, hot, gas-particle flows. They represent the most hazardous events of explosive volcanism, one striking example being the famous historical eruption of Pompeii (AD 79) at Vesuvius. Much of our knowledge on the mechanics of pyroclastic flows comes from theoretical models and numerical simulations. Valuable data are also stored in the geological record of past eruptions,
Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatrem... more Discrete explosive bursts, or explosions, are known from many volcanic eruptions. In maar-diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in
High Temperatures-High Pressures, 2002
ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough... more ABSTRACT To simulate and predict the behaviour of a lava flow, it is essential to have a thorough knowledge of its thermophysical properties. Therefore, thermal conductivity, specific heat, and viscosity of volcanic rock material were determined in a wide temperature range. Especially, the properties of the molten material were investigated in detail. The material was taken from the Pietre-Cotte lava flow located on the isle of Vulcano, north of Sicily. The thermal conductivity of the material was determined in the temperature range 293 - 1623 K by the hot-wire method. Melting occurs above HOOK The specific heat was measured by differential scanning calorimetry between 347 and 1671 K. The viscosity of the lava melt was determined with a rotational viscometer HAAKE M5. The viscometer was enclosed in a high-temperature furnace optimised for the temperature range 1373 - 1598 K.
Eos, Transactions American Geophysical Union, 2007
Nuclear Engineering and Design, 1995
An experimental set-up for the generation of mixtures of silicate melt (remotten volcanic rocks) ... more An experimental set-up for the generation of mixtures of silicate melt (remotten volcanic rocks) and water and the triggering of steam explosions was built at the Institut fur Kemenergetik (IKE) at Stuttgart. The temperature of melts investigated ranged from 1200 to 1600 °C. The chosen experimental configuration resulted in mixtures of 0.5-20 ml of water in 125 ml of melt, the water dispersed into droplets that were entrapped by domains of melt. More than 300 experimental runs were performed using a variety of remolten volcanic rocks. Explosive premixtures were triggered by shock waves of less than 8 J kinetic energy. Only part of the melt and part of the water of the mixture reacted thermally, thus causing an explosion. The most intensive explosions were produced by reaction of about 3 ml of water and 6 ml of melt and released kinetic energy of more than 600 J. Higher melt viscosity resulted in weaker explosions. Higher mixing energy enhanced probability and intensity of explosions. Melt temperatures were only of minor influence. If bubbles of non-condensible gases were abundant in a mixture of otherwise explosive water/melt ratio, explosions could not be triggered.
Nature, 1999
... We find that surface features of ash grains can be used to identify the dynamic contact of ma... more ... We find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water. ... Deadline: Jun 18 2011; Reward: Varies. Material supply of non-commercial compounds matching the shown core structure is desired. The Seek ...
Journal of Volcanology and Geothermal Research, 2007
Molten-Fuel-Coolant Interaction (MFCI) experiments were performed using remelted foiditic rock sa... more Molten-Fuel-Coolant Interaction (MFCI) experiments were performed using remelted foiditic rock samples from the West Eifel volcanic field (Germany). Two experimental series were carried out with one magmatic melt and two water compositions. Bidistilled water was used in the first series (DW-1 to DW-5). In the second series (SW-1 to SW-5), the bi-distilled water was saturated (350 g L − 1 ) with sodium chloride (NaCl). For both experimental series the fragmentation history and the energy release were recorded and compared. The smallest particles (≤125 μm) were studied using scanning electron microscopy (SEM). Most MFCI experiments with bi-distilled water reached higher explosion intensities than the experiments with the saline water. This was accompanied by higher particle ejection velocities as well as the formation of more fine-grained and more interactive particles of angular shape. Additionally, the smallest artificial pyroclasts were examined by evolved gas analyses (EGA). The particles from the MFCI experiments with salt solutions are found to contain more sodium hydroxide (NaOH). These observations can be explained by thermodynamic arguments. In contrast to the MFCI experiments with pure water, an additional reaction occurs with saline water that results in evolution of hydrogen chloride (HCl) gas and leaves a residue of sodium hydroxide. The MFCI process with saline water consumes more enthalpy and Gibbs free energy, so that less energy is available for the explosion. With other sodium halides dissolved in the water (NaF, NaBr or NaI) the additional reaction can be predicted to have greater or lesser effects on phreatomagmatic explosions.
Journal of Volcanology and Geothermal Research, 2011
A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic... more A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic rocks using wide gap viscometry. The complex composition of magmatic melts leads to complicated rheologic behavior which cannot be described with one simple model. Therefore, measurement procedures which are able to quantify non-Newtonian behavior have to be employed. Furthermore, the experimental apparatus must be able to deal with inhomogeneities of magmatic melts. We measured the viscosity of a set of materials representing a broad range of volcanic processes. For the lower viscous melts (low-silica compositions), non-Newtonian behavior is observed, whereas the high-silica melts show Newtonian behavior in the measured temperature and shear rate range (T = 1423 K − 1623 K, γ̇=10 − 2 s − 1 − 20 s − 1 ). The non-Newtonian materials show power-law behavior. The measured viscosities η and power-law indexes m lie in the intervals 8 Pa s ≤ η ≤ 210 3 Pa s, 0.71 ≤ m ≤ 1.0 (Grímsvötn basalt), 0.9 Pa s ≤ η ≤ 350 Pa s, 0.61 ≤ m ≤ 0.93 (Hohenstoffeln olivine-melilitite), and 8 Pa s ≤ η ≤ 1.510 4 Pa s, 0.55 ≤ m ≤ 1.0 (Sommata basalt). Measured viscosities of the Newtonian high-silica melts lie in the range 10 4 Pa s ≤ η ≤ 310 5 Pa s.
Journal of Volcanology and Geothermal Research, 2008
Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, the... more Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material,
Journal of Volcanology and Geothermal Research, 2002
In addition to large amounts of fragmented country rocks, maar^diatreme volcanoes commonly eject ... more In addition to large amounts of fragmented country rocks, maar^diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and/or xenocrysts derived from the country rocks surrounding the diatremes. Formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences. The thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks. Vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks. Surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass-flow deposit subsequent to each explosion. When, prior to a new explosion, magma rises from the underlying feeder dyke into the root zone, it intrudes this clastic debris, inflates it and may mingle with the debris to form a peperite. Subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains, juvenile lapilli and bombs containing xenoliths or xenocrysts from the country-rock debris. Lack of further explosions, but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs. ß
Journal of Volcanology and Geothermal Research, 2002
Hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key... more Hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites. Experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process. These studies show that for a wide range of shear rates a laminar flow behaviour of the system magma^liquefied sediment can be expected, i.e. turbulent mingling is not a realistic scenario. Formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities. In addition to the hydrodynamics, cooling processes must also be considered during peperite formation. Calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time. The consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable. However, as smaller domain sizes (peperitic grain sizes) exist in nature, we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes. ß 2002 Published by Elsevier Science B.V.
Journal of Volcanology and Geothermal Research, 1998
Journal of Volcanology and Geothermal Research, 1998
Detailed field investigations of kimberlite pipes of the Upper Cretaceous Gibeon Kimberlite Field... more Detailed field investigations of kimberlite pipes of the Upper Cretaceous Gibeon Kimberlite Field in southern Namibia revealed geologic features which do neither agree with extensive nor with explosive vesiculation. In the pipe Hanaus 2, vesicle-free magmatic kimberlite intruded the diatreme as a plug. Here we report on the first experiments in which phreatomagmatic explosions were produced with remolten natural, non-fragmental magmatic kimberlite from the Hanaus 2 central plug as a best fit model kimberlite magma system. After water was injected into the melt under controlled conditions, Ž . the resulting water-melt mix was triggered by a low-energy shock wave -1 J and a violent explosion was obtained: High-energy shock waves of several 1000 J were generated and pyroclasts were ejected with a maximum speed ) 400 mrs. q 1998 Elsevier Science B.V.
Journal of Geophysical Research, 2006
The release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard a... more The release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard assessment and civil defense. The explosive production of volcanic ash by intensive fragmentation of magma and host rocks represents a substantial part of this energy. For cases of explosive eruption where predominantly host rock was fragmented (phreatomagmatic eruptions) to form the major part of volcanic
Journal of Geophysical Research, 2008
... Adapted from Siebe et al. [1993] and Siebert and Carrasco-Nún˜ez [2002]. B11201 AUSTIN-ERICKS... more ... Adapted from Siebe et al. [1993] and Siebert and Carrasco-Nún˜ez [2002]. B11201 AUSTIN-ERICKSON ET AL.: PHREATOMAGMATIC EXPLOSIONS OF RHYOLITE 3 of 12 B11201 Page 4. ... al., 2003; Rust et al., 2004; Castro et al., 2005; Gonnermann and Manga, 2005]. ...
Journal of Geophysical Research, 2007
1] A newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindr... more 1] A newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products (tephra). Blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas. Opening of fast solenoid valves results in impulse-like coupling of the released gas to the sample. The system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition. Depending on the specific mechanical energy (SME) of the system, which results from DPV/m, where DP is gas overpressure (i.e., pressure > atmospheric), V is gas volume, and m is sample mass, different behaviors are observed. If SME > 2.6 kJ/kg, a dilute plume develops, and particles are sedimented by fallout exclusively. If SME < 1.5 kJ/kg, the exiting column collapses and develops a shear current similar to a pyroclastic flow. The Reynolds number of the shear currents is >10 6 , implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments. The measured shear current velocities are proportional to the impact mass flow rate, i.e., the product of mixture density and impact velocity. Experimental data and grain-size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows.