Lars Enok Engvik

• Engvik, Lars Enok; Stockhert, Bernhard & Engvik, Ane Karine (2009). Fluid infiltration, heat transport, and healing of microcracks in the damage zone of magmatic veins: Numerical modeling. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 114. doi: 10.1029/2008JB005880. Vis sammendrag

  Alteration halos with sharp boundaries are flanking pegmatitic veins in high-grade metamorphic and magmatic rocks of Dronning Maud Land, Antarctica. These halos are interpreted to represent the damage zone, formed as the wake of the process zone at the tip of the propagating magma-filled fracture and infiltrated by the fluid phase liberated from the crystallizing hydrous melt. On the basis of a set of assumptions, our numerical model explores the time scales of the infiltration processes, taking into account the combined effects of fluid flow, heat transfer, and temperature-dependent decay of interconnected porosity due to microcrack healing. Assuming an initial magma temperature of 700 degrees C, a far field temperature in the host rock of 300 degrees C, an initial porosity range of 0.5-2% in the damage zone, a permeability of 10(-16) m(2), and a pressure difference of 300 MPa, we find that the fluid infiltration into the damage zone proceeds within seconds to minutes and that the fluid flow contributes significantly to the heat transfer into the host rock. Assuming an initial microcrack aperture of 1 mu m, the model predicts that the crack healing time scale is significantly longer than that of fluid infiltration in the case of thin veins with narrow damage zones; in this case, crack healing does not hinder fluid infiltration. Only for thick veins with high heat content and prolonged crystallization history does permeability become reduced by crack healing during progressive fluid infiltration. The results indicate that the formation of the alteration halos flanking pegmatitic veins may be a quasi-instantaneous process on geological time scales.

• De Blasio, Fabio Vittorio; Elverhøi, Anders; Engvik, Lars; Issler, Dieter; Gauer, Peter & Harbitz, Carl Bonnevie (2006). Understanding the high mobility of subaqueous debris flows. Norsk Geologisk Tidsskrift. ISSN 0029-196X. 86. Vis sammendrag

  Submarine mass wasting in the form of glacial mudflows, river-laden debris flows, rock avalanches, sandy debris flows, outrunner blocks, or turbidity currents, reveal an extraordinary mobility, demonstrated by the very long runout distance between the source area and the final deposit, even on very gentle gradients. Laboratory experiments reveal that the dynamical behaviour of artificial debris flows depends dramatically on the claysand ratio in the experimental slurry. Artificial debris flows with high clay content, which are possibly a realistic replica of mudflows in glaciallyinfluenced areas, tend to form a thin water layer underneath the head which acts as a natural lubricant. In contrast, lubrication cannot be easily invoked for sand-rich gravity flows. Experiments show that sandy debris flows lack cohesion, and that sand settles quickly during the rapid disaggregating phase. In the present work we review the field data, experimental results gained with debris flows of various compositions, and the status of theoretical studies and numerical simulations of submarine debris flows. When dealing with debris flows that remain compact, such as clay-rich debris flows and outrunner blocks, both experiments and simulations indicate the importance of water lubrication for mobility. On the other hand, sandy debris flows are far more complicated owing to the increased importance of water penetration, disintegration, and turbulence, and these difficulties are reflected in greater intricacy of experiments and computer simulations. Thus, the problem of whether sandy debris flows may be highly mobile in the natural setting still remains elusive.

• Engvik, Lars; De Blasio, Fabio Vittorio & Elverhøi, Anders (2006). Small scale simulations of outrunner blocks. Norsk Geologisk Tidsskrift. ISSN 0029-196X. 86. Vis sammendrag

  Submarine debris flows are often accompanied by isolated blocks located some distance beyond the rest of the failed mass. These so-called outrunner blocks have the ability to travel over long distances on very gentle slopes. Glide tracks of various depths are observed in some cases, while in others no traces of significant erosion can be detected, which indicates that outrunner blocks are able to travel completely separated from the bed. Similar phenomena occur in laboratory experiments, where chunks detach from the front of a small-scale debris flow and move out ahead of the rest of the flow.We present a two-dimensional, small-scale model of a rigid block subjected to gravity combined with the complete dynamical interaction with the surrounding liquid. Our simulations indicate that the block is able to hydroplane completely separated from the bed and attain long runout distances. The maximum velocity of the block is close correlated with the thickness of the block. For the simple shape assumed in our model we find that the densimetric Froude number is ?0.8 . Depending on the geometrical shape of the block, size and the slope angle, we observe oscillatory motion, where the front of the block is lifted periodically and the rear part tends to scrape the bed. The pressure distribution around the block indicates that the block is likely to deform at the rear end as well as the front.

• De Blasio, Fabio Vittorio; Engvik, Lars & Elverhøi, Anders (2006). Sliding of outrunner blocks from submarine landslides. Geophysical Research Letters. ISSN 0094-8276. 33(L06614). Vis sammendrag

  Outrunner blocks are nearly intact pieces of debris that detach from a slowing-down submarine landslide and flow ahead of the front. Data gathered from different sliding areas highlight some properties of outrunner blocks and in particular their inordinate mobility reflected in runouts of up to 25 kilometres, even on very gentle slopes. Blocks may produce an erosion glide track on the sea floor few centimetres to several metres deep, which in some cases exhibits regularly spaced grooves along the flow direction. Understanding the dynamics of outrunner blocks may shed light on the flow and lubrication of submarine landslides. We develop a simple hydrodynamic model of a rigid block interacting with ambient water and subject to lubrication with the sea floor, and calculate numerically the equation of motion for the block. We find that as a consequence of lift forces and water lubrication, the block may reach long runouts, in agreement with data. When the block is moving at high speed, we find an oscillating solution to the equations of motion which could explain the creation of dashed grooves.

• Ilstad, Trygve; De Blasio, Fabio Vittorio; Elverhøi, Anders; Harbitz, Carl Bonnevie; Engvik, Lars & Longva, Oddvar (2004). On the frontal dynamics and morphology of submarine debris flows. Marine Geology. ISSN 0025-3227. 213(4), s. 481–497. Vis sammendrag

  Several submarine debris flows show an apparently chaoticfrontal part with blocks of variable size (from roughly tensto some hundreds of metres) located some distance beyond thefront of the main deposits. This outrunner phenomenon was studied both in the field and in laboratory experiments. Depositional patterns in a field case (Finneidfjord, northern Norway) are classified from the outer distal part of the debris flow to the outermost outrunner block. Similar patterns were found in experimental debris flows, and we suggest that flow processes in the laboratory are applicable to the field example. Theoretical investigations are applied to assess frontal dynamics and especially the formation and motion of outrunner blocks. As the front of the debris flow pushes through ambientwater, a combination of front pressure and lift force allowsfor intrusion of a water layer underneath the front (hydroplaning). This water layer reduces basal friction and induces tensile stresses farther behind the front, leading to a possible detachment and decoupling with respect to the main slide body. These outrunner blocks show an increased mobility compared to the main slide body and deposition of such blocks may occur far away from the main slide body.

• De Blasio, Fabio Vittorio; Engvik, Lars; Elverhøi, Anders & Harbitz, Carl Bonnevie (2004). Hydroplaning and submarine debris flows. Journal of Geophysical Research (JGR). ISSN 0148-0227. 109. Vis sammendrag

  Examination of submarine clastic deposits along the continental margins reveals the remnants of holocenic or older debris flows with run-out distances up to hundreds of kilometers. Laboratory experiments on subaqueous debris flows, where typically one tenth of a cubic meter of material is dropped down a flume, also show high velocities and long run-out distances compared to subaerial debris flows. Moreover, they show the tendency of the head of the flow to run out ahead of the rest of the body. The experiments reveal the possible clue to the mechanism of long run-out. This mechanism, called hydroplaning, begins as the dynamic pressure at the front of the debris flow becomes of the order of the pressure exerted by the weight of the sediment. In such conditions a layer of water can intrude under the sediment with a lubrication effect and a decrease in the resistance forces between the sediment and the seabed. A physical-mathematical model of hydroplaning is presented and investigated numerically. The model is applied toboth laboratory- and field-scale debris flows. Agreement with laboratory experiments makes us confident in the extrapolation of our model to natural flows and shows that long run-outdistances can be naturally attained.

• Elverhøi, Anders; De Blasio, Fabio Vittorio; Butt, Faisal Ahmed; Issler, Dieter; Harbitz, Carl Bonnevie & Engvik, Lars [Vis alle 8 forfattere av denne artikkelen] (2002). Submarine mass-wasting on glacially-influenced continental slopes: processes and dynamics. ?. 203, s. 73–87. Vis sammendrag

  Submarine slides and debris flows are common and effective mechanisms of sediment transfer from the continental shelf to deeper parts of the basin. They are particularly common along glaciated margins that have experienced high sediment fluxes to the shelf break during and after glacial maxima. During one single event, typically lasting for a few hours or less, enormous sediment volumes can be transported over distances exceeding hundreds of kilometres, even on very gentle slopes. In order to understand the physics of these mass flows, one ideally divides the process into a release phase, followed by break-up, flow and final deposition. Little is presently known regarding the release and break-up, although some plausible explanations can be inferred from basic mechanics of granular materials. Once initiated, the flow of clay-rich or muddy sediments may be assumed to behave as a (non-Newtonian) Herschel-Bulkley fluid. Fluid dynamic concepts can then be applied to describe the flow provided the rheological properties of the material are known. Numerical modelling supports our assertion that the long runout distances observed for large volumes of sediments moving down gentle slopes can be explained by partial hydroplaning of the flowing mass. Hydroplaning might also explain the sharp decrease of the friction coefficient for submarine mass flows as a function of the released volume. The paper emphasises the need for a better understanding of the physics of mass wasting in the submarine environment.

• Engvik, Lars; Hjorth-Jensen, Morten; Osnes, Eivind; Bao, G. & Østgård, Erlend (1996). Asymmetric Nuclear Matter and Neutron Star Properties. The Astrophysical Journal (ApJ). ISSN 0004-637X. 469.

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• Engvik, Ane & Engvik, Lars (2023). 18 kg avfall per kvadratmeter. Tidens Krav.
• Engvik, Lars & Angell, Linn Inger S. (2022). Skal forske og undervise : Lars Engvik er nyansatt førsteamanuensis i Kristiansund. [Avis]. Tidens Krav.
• Engvik, Ane Karine; Stockhert, Bernhard & Engvik, Lars (2007). Fluid infiltration in low permeable rocks - modeling of fluid transport, heat transfer and healing of microcracks (Dronning Maud Land, Antarctica). Vis sammendrag

  Conspicuous alteration halos flank pegmatitic veins in high grade metamorphic rocks exposed in Dronning Maud land, Antarctica. The alteration halos are interpreted to represent the damage zone, formed as the wake of the process zone at the tip of the propagating fractures. Within the halos, the density of microcracks in quartz and feldspar exceeds that observed in the unaltered host rock by one order of magnitude. Fluids liberated from the hydrous melt forming the central vein have infiltrated the damaged zone, giving rise to alteration. Based on the qualitative model proposed by Engvik et al. (2005), here the fluid infiltration and healing time scales are investigated using a numerical model taking into account the combined effects of fluid flow, heat transfer and temperature dependent crack healing rates. The interconnected porosity of the damaged zone decreases with time due to crack healing. The healing rate is strongly temperature dependent. Assuming an initial porosity of the damaged zone of 0.5% and 2% , a permeability of and a pressure difference of 300 MPa, we find that the fluid infiltration into the damage zone is rapid and that the fluid flow contributes significantly to the heat transfer into the host rock. The fluid front reaches 10 cm into the damaged zone within a few seconds and 1 meter within minutes. Assuming an initial temperature in the pegmatic melt of 700°C and a host rock temperature of 300°C, the heat is transported 0.08 m in 6 minutes. The crack healing time scale is generally longer than that of fluid infiltration, i.e. the microcracks heal after fluid infiltration is completed. The healing rates are strongly temperature dependent, however, and the healing times in the wide damage zone associated with thick central veins increases significantly with increasing distance to the contact with the magma. By considering microcracks with initial aperture of 1 _mm, we find that these cracks may be complete healed within a few hours close to the central vein and within a few days up to a year at larger distances, depending on the activation energy for crack healing.

• Engvik, Lars (2006). The motion of submerged objects falling down an inclined plane, Preceedings of the NORDIC Comsol Conference 2006 Copenhagen. COMSOL A/S. Vis sammendrag

  The aim of this work is to study the motion of a rigid streamlined object close to an inclined plane. A two-dimensional, small-scale model of a rigid block subjected to gravity is presented combined with the complete dynamical interaction with the surrounding liquid. Both the linear and rotational equations of motion of the body are coupled to the Navier-Stokes equations for the fluid flow using Comsol Multiphysics. A circulation of the fluid around the body is observed, and it generates a strong lift force that is sufficient to keep it completely separated from the bed, while it is travelling down slope. This water lubricating effect, also called hydroplaning has been recognized as an important effect to explain an extraordinary mobility of submarine slides. For the simple shapes studied in this work, we find that the motion becomes unsteady if the densimetric Froude exceeds 0.7.

• Engvik, Lars (2006). The motion of submerged objects falling down an inclined plane. Vis sammendrag

  The aim of this work is to study the motion of a rigid streamlined object close to an inclined plane. A two-dimensional, small-scale model of a rigid block subjected to gravity is presented combined with the complete dynamical interaction with the surrounding liquid. Both the linear and rotational equations of motion of the body are coupled to the Navier-Stokes equations for the fluid flow using Comsol Multiphysics. A circulation of the fluid around the body is observed, and it generates a strong lift force that is sufficient to keep it completely separated from the bed, while it is travelling down slope. This water lubricating effect, also called hydroplaning has been recognized as an important effect to explain an extraordinary mobility of submarine slides. For the simple shapes studied in this work, we find that the motion becomes unsteady if the densimetric Froude exceeds 0.7.

• Engvik, Ane Karine; Stockert, Bernard & Engvik, Lars (2006). Numerical modelling of fluid infiltration, heat transport and healing of microcracks during magma-driven hydraulic fracturing. Vis sammendrag

  Excellent outcrops in Dronning Maud Land, Antarctica, provide unique insight into the mode and extent of fluid infiltration into metamorphic and plutonic rocks in the middle crust. CO2 -H2O-dominated fluids are liberated from pegmatitic veins and give rise to alteration halos. In the alteration halos, the conspicuous change in colour is correlated with hydration mineral reactions and high density of microcracks in quartz and feldspar exceeding that observed in the unaltered host rock by an order of magnitude. The field relations indicate that the veins originated as melt driven hydraulic fractures, sealed by pegmatite and aplite crystallizing from volatile-rich melts, with the alteration halo being the wake of the process zone formed at the tip of the propagating fractures. The fluid infiltration and healing time scales are investigated using a numerical model which takes into account the combined effects of fluid flow, heat transfer and temperature dependent healing rates. We assume that the damage zone is a porous medium with low permeability. The porosity is assumed to be independent of pore pressure, but reduces with time according to a strongly temperature dependent healing process. Initially, the damage zone is assumed homogenous with porosity of 5% and permeability of 1016 m2 and all the fluid is located in the magmatic vein-fill. We use a one-dimensional dynamic model, where the fluid as well as heat is transported through the host rock perpendicular to the interface between the magma and host rock. We find that the fluid infiltration into the damage zone is rapid and that the fluid flow contributes significantly to the heat transport through the host rock. With pressure difference of 300 MPa, the fluid is able to infiltrate a region of 0.25 m depth in one minute and one meter within 15 minutes. Assuming an initial temperature on the magma of 700 °C and a host rock temperature of 300 °C, the heat will be transported 0.07 m in one minute and 0.2 m within 15 minutes. The healing time scale is generally longer than that of the fluid infiltration, and the microcracks heal after fluid infiltration is completed. However the healing processes are strongly temperature dependent and the healing time increases significantly with the distance to the centralvein. By considering microcracks with initial aperture of 1 µm, we find that these cracks may be completely healed within one hour close to the central vein and by up to a year at large distances. For larger apertures, e.g. of 3 µm, the healing time scales up to typically one day close to the central vein and tens of years at large distances. Engvik, A.K., Stöckhert, B. & Engvik, L. (2006) Numerical modelling of fluid infiltration, heat transport and healing of microcracks during magma-driven hydraulic fracturing. EGU General assembly, Vienna, 2006.

• De Blasio, Fabio Vittorio; Elverhøi, Anders; Engvik, Lars; Issler, Dieter; Gauer, Peter & Harbitz, Carl Bonnevie (2005). Understanding the high mobility of subaqueous debris flows. Vis sammendrag

  Submarine mass wasting shows a variety of forms like glacial mudflows, river-laden sedimentary failures, rock avalanches, sandy debris flows, outrunner blocks, or turbidity currents. In most cases, submarine mass flows reveal an extraordinary mobility, demonstrated by the very long runout distance between the source area and the final deposit, even on very gentle gradients. As an example, the front of the giant Storegga landslide in the Norwegian Sea covered a maximum distance of more than four hundred kilometres, running on an average slope angle of about one degree. This high mobility seems to affect all kinds of gravity mass flows, irrespective of the composition and grain size. Laboratory experiments, however, reveal that the dynamical behaviour of artificial debris flows depends dramatically on the clay-sand ratio in the experimental slurry. Artificial debris flows with high clay content, which are possibly a good replica of mudflows in glacially-influenced areas, tend to form a thin water layer at the front which acts as a natural lubricant. In contrast, lubrication cannot be easily invoked for sand-rich gravity flows. Indeed, the experiments show that sandy debris flows lack cohesion, and that sand settles quickly during the rapid disaggregating phase. In the present work, after briefly reviewing the field data, we present the experimental results gained with debris flows of various compositions, and finally examine the status of theoretical studies and numerical simulations of submarine debris flows. When dealing with debris flows which stay compact, such as clay-rich debris flows and outrunner blocks, the simulations reproduce well the lubrication effect seen in the experiments. On the other hand, sandy debris flows are far more complicated owing to the increased importance of water penetration, disintegration, and turbulence, and these difficulties will be reflected in greater intricacy with computer simulations. Thus, the problem of whether sandy debris flows may be highly mobile in the natural setting still remains elusive. We suggest some experiments and numerical models that might shed some light on this problem.

• Engvik, Lars; De Blasio, Fabio Vittorio & Elverhøi, Anders (2005). Small scale simulations of outrunner blocks. Vis sammendrag

  Nedenfor undersjøiske skredavsetninger kan en ofte nedenfor finne løsrevne blokker som har beveget seg en betydelig avstand uten å brekke opp. Disse skredblokkene har vist seg å kunne bevege seg over store avstander med meget liten helning. De opptrer både i forbindelse med undersjøiske skred i eksperimentelle småskalaeksperimenter, så vel som i stor skala på havbunnen. En numerisk modell er utviklet som beskriver de viktigste delene av dynamikken til skredblokk. Beregninger er utført for ulike helningsvinkler og skredblokker med ulik geometrisk form ved små og moderate Reynolds tall. Resultatene er konsistente med observasjoner i eksperimenter. En kritisk hastighet blir påvist der blokkens front løfter seg og den videre bevegelsen blir ustabil. Den kritiske hastigheten avhenger hovedsakelig av tykkelsen til blokken. Submarine debris flows deposits are often accompanied by isolated blocks located some distance beyond the rest of the failed mass. These so-called outrunner blocks have proven the ability to travel over long distances on very gentle slopes. This phenomenon is observed at small scale experimental slides as well as in field scale. The aim of this work is to separate some of the most important features of the dynamics of outrunner blocks and study them in more detail in a manageable model. Simulations have been performed for several slope angles, shapes of the block at low and moderate Reynolds numbers. The results are consistent with experiments. A critical velocity is found, which is mainly related to the thickness of the block, where the front of the block lifts up and the motion become unstable.

• Engvik, Lars (2003). Datasimuleringer -en raskere veg til teknologisk utvikling? Vis sammendrag

  - Presentasjon av et prosjekt ved Høgskolen i Sør-Trøndelag, Avdeling for teknologi. "Tekniske beregninger innen ingeniørfag" Data-simuleringer benyttes i stor grad innenfor ulike fagfelt ved Høgskolen i Sør-Trøndelag, Avdeling for teknologi. Datasimuleringer anvendt i forbindelse med teknologiske problemstillinger er i mange tilfeller kostnads- og tidsbesparende. Det er et fleksibelt redskap i moderne undervisning innen teknologiske fag. Det har fordeler ved at alle fysiske størrelser tilgjengelig for de problemstillingene man studerer. Resultatene som oppnås ved data-simuleringer må imidlertid behandles kritisk. Det er av vital betydning at datasimuleringer benyttes i nær tilknytning til eksperimentell virksomhet. Resultatene som oppnås kan i stor grad være avhengig av matematiske/ fysiske modeller (tilnærmelser og forenklinger) som ligger til grunn, samt numerisk pålitelighet. Datasimuleringer stiller store krav til faglig kompetanse og ressurser når det gjelder datakraft. Ved avdelingen har vi derfor forsøkt å samordne aktiviteten i forbindelse med datasimuleringer på tvers av fagdisipliner og dra nytte av kompetansen i de ulike miljøene og gjøre aktiviteten mer kostnadseffektiv. Videre er intensjonen å øke forskningsaktiviteten på de ulike fagfeltene innen forskning såvel som undervisning ved økt bruk av datasimuleringer

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