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Home Discussions Workshop Market Broadcasts. Change language. Install Steam. Pavonis Interactive This user has also played as:. Louisville, Colorado, United States. Level 3. The is the official Steam home for Pavonis Interactive Inc. To stay on top of our work, visit our web page at www. Sorry but this account can't accept Friend requests! View more info. Currently Offline. Pungent Raindeer King Online. JoINrbs Online. Viralninja Last Online 2 days ago.
Pete van de Pete 22 Sep am. Hello i just wanna say one thing: Respect for You People. Long War EW is one of most enjoyable experience for me,since long time. Here we only note the special considerations that apply to this more general formulation. The right hand side of 1 indicates that volume is lost from the active component as a rate process, as can be seen from the analysis of its dimensions. In 1 , losses due to both margin formation and degassing are considered important.
However, to simultaneously determine the change in density due to degassing and the flow thickness profile, we need to add a mass conservation equation.
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The solution of this more complicated system is beyond the scope of this paper. The implications of volume loss due to degassing are presented in the discussion. Thus the remainder of this section considers only the volume loss due to the removal of material from the active component to stationary margins. However, it is more convenient to deal with length scales representing these processes.
Such length scales can readily be compared with the actual lengths of flows. The length scale in 2 is the primary measure we use here to characterize the importance of mass losses to stationary margins as the flow advances. But such considerations require additional assumptions and increase the complexity of the mathematics significantly [ Baloga and Pieri , ; Baloga , ].
The influence of time dependence will be reserved for future analyses. Since little is presently known about this process, we make the simplest assumptions possible.
We assume that the rate of volume loss at any point along the flow path is a constant. With this simplifying assumption, 1 reduces to This equation has the elementary solution From 4 , we will show how to develop inferences about rheologic change from flow thickness, width, and underlying slope data when Q is given explicitly in terms of these variables. However, the unknown parameter L m must be evaluated before we can use the dimensional data to estimate the viscosity change. First, systematic changes in the thickness and width of the flow are interpreted here as responses of the flow to changes in the preexisting topography or the bulk viscosity of the lava.
Second, the rate of volume loss to the stationary margins is taken as a constant at all locations along the flow path. Thus the contribution to stationary components is proportional to the length of time they are supplied with lava. Each of these assumptions are stringent and further investigations are required. All of the volume discharged from the vent must be accounted for in either the active or stationary components when there is no degassing.
This links the relative volumes of the active and passive components to the total volume discharged. In effect, this link provides a means for evaluating the unknown length scale L m appearing in 6. As L m becomes less and less, the more vigorous these processes are and the time of transit increases. Physically interpreted, lava is removed from the active component due to margin building at higher rates at each location along the path of the flow as L m decreases. This diminishes the flow rate at each step, thus engendering longer and longer transit times as L m decreases. The denominator, in effect, corrects for this so that all volume is accounted for between the two components at all times.
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The difference in times on the right hand side of 9 thus starts the loss to the stationary component at the location of dx only when the flow front arrives at t a x. These are quantities that can be estimated from the MOLA and imaging data available at present. Ergo, we can write the ratio of volume in the stationary margins to the total volume of lava erupted as where Equations 12 and 13 provide the key to obtaining the unknown parameter L m when estimates of the relative volumes of the active and passive components are known.
By inspection of these two equations, it is evident that there is only dimensional data and L m present. However, given the dimensional data for any flow, the full range of L m can be inserted into these equations, producing a single curve for the relative volume in the stationary components. Once this parameter is obtained, viscosity estimates can be computed from 6. This procedure is illustrated below for the flow shown in Figure 3. It is one of at least a dozen that can be seen to flow north from the rift zone.
These north trending flows are all mapped as unit Apm1 by Scott et al. There are a series of small domes on the rift zone, but no elongated vent, fissure, or dome can be unambiguously identified as the source of the flow. The middle portion of the flow is cut by a 65 km diameter impact crater at 8. The relief of this flow over the distal segment we analyze here is significantly greater than the variations in the ambient topography. Thus, even though the flow is north trending, these data are more than adequate to discern the systematic behavior of the flow thickness. Given the north trending orientation of the flow, the extraction of the longitudinal thickness profile from individual MOLA transects by the method of Glaze et al.
To ensure that these profiles were indeed perpendicular to the flow direction, we generated a local contour map and took profiles that started and ended at a constant elevation. This thickness was determined relative to the best estimate of the ambient topography for each profile. There is a difference between the slope measured along the center of the flow and that which might be obtained along the edges. However, the absolute values of the slopes are so small, and the extent of the flow is so long, that this factor is inconsequential.
For shorter flows with relatively rapid thickening [see, e. This channel is best seen in Figure 5. Our interest here is in the overall volumes of lava contained in the active and passive parts of the flow. At some points along the flow, no channel is evident and thus the entire width of the flow is assumed to be active. Estimates of the volume fraction contained in stagnant margins are based on individual profiles as well as image and gridded topography data for the entire km extent.
Figure 6 shows several typical profiles along the channelized portion of the flow. Each of the transects was inspected to determine the width of the flow at these points and the representative thickness of the flow relative to the ambient topography. Figure 7 graphically illustrates the width and thickness as functions of distance along the flow. The slope of the underlying topography was estimated from the data presented in Figure 4. Prudent judgments were made by inspecting each profile to compile the entries into Table 2.
The results of the computations using the dimensional data and the formulas above are shown in Figure 8. Thus we use the total width of the flow as the active width. From inspection of Figure 8 , we find the unexpected result that there is hardly any increase in the viscosity. There is in fact less than an order of magnitude increase over a distance of almost km.
By comparison with large terrestrial basalts, e. It retained its integrity as it traveled the last km. During emplacement, the flow must have shielded the inner core from significant heat losses that would engender viscosity change due to thermal losses. This curve was computed according to 12 and 13 with the dimensional data in Table 2. Once we have obtained the value of L m , we can use it in 6 to recompute the viscosity change. We have estimated this fraction in two ways. First we have directly examined the transects from the shaded relief gridded topography data to identify the ratio of the final channel width to the total flow width.
We have used wedge shaped levees as a general formula for estimating the passive volume, although many different shapes are evident in the actual transects.
From Figure 9 , we estimate that the length scales corresponding to these two volume fractions are km and km respectively. We consider the latter estimate to be extremely conservative on the basis of our estimates of the stationary volume. The results are shown as the upper two curves in Figure 8.
Except for the most distant segment, the increase in viscosity is only about an order of magnitude over the entire length of the flow. When margin building is taken into account, the dominant variable remains the amount of thickening with distance. And, like many other flows on Mars, there is simply not a great deal of thickening with distance. For the most part, the flow accommodated the shallowing of the underlying slope by lateral expansion and only a very modest thickening. Thus our conclusion is that, although lava was being lost from the active advancing component to the stationary component, this process did not interfere with the dominant dynamics of simple viscous flow.
Complex emplacement involving layers and multiple events is not the most likely scenario. Second, none of the physical processes that cause large viscosity increases in terrestrial flows [ Moore , ; Crisp et al. We might have expected a larger increase due to radiation from exposed inner core, temperature losses, crystallization, disruption of streamlines and various forms of surface renewal.
This does not appear to be the case because the flow does not thicken appreciably. This suggests that a balance existed between the shielding and shedding, which evidently must have been very robust in long lava flows because it seems to occur often on Mars. The ability to maintain such a balance probably depends on low, relatively smooth slopes to avoid vigorous disruption of internal flow streamlines and processes that continually expose the hotter inner core [ Crisp et al.
This argues for more vigorous discharge, terrain that is rougher on the scale of the flows, or similar factors that could cause higher thermal losses. Given the large width of the Pavonis flow, the large flow rate of the former case the lower viscosity is not unexpected.
In the latter case the higher viscosity , the volumetric flow rate is a reasonable extrapolation of values estimated for some terrestrial eruptions. At present, we know of no way to preclude either of these limits for emplacement times. These and other studies [ Einarsson et al. This would permit the relative influences of viscosity changes, losses to passive components, and density changes to be resolved. In this scenario volume conservation would be described by and an independent equation for the conservation of mass might be taken as It is interesting that, if the assumption of steady state is now evoked, 14 and 15 require that Systematic density changes along the path of the flow, as described by Moore [ , ] , Lipman and Banks  , and Baloga et al.
The effusion rate of the Mauna Loa eruption remained essentially constant while time changes in the density occurred [ Lipman and Banks , ]. Consequently, there are two obvious avenues for extending the approach presented here. Second, permitting a variable rate loss to the stationary margins is more in accord with terrestrial experience. So we will take the results of our analysis of the Pavonis flow from Section 3 as givens and compare the potential influence of degassing to the constant density case.
To compare the case of degassing to the constant density case, we note that the initial flow rates must satisfy to produce flows of length L , where Q do is the initial flow rate for the degassing case. Thus we can solve for the degassing length scale in terms of the flow rate ratio required to produce the same flow length: Viscosity estimates for the Pavonis flow are shown in Figure 10 for the case when the initial degassing flow rate is twice that for the case with no degassing.
Because degassing diminishes the flow rate, the changes in viscosity are systematically higher than the constant density case, as would be expected. However, the difference between the degassing and no degassing cases is small compared to the overall relative change. Again, this indicates that degassing is not important and that this flow must move as a coherent viscous fluid.
The MOLA gridded topography is adequate for the present task because the flow is a few tens of kilometers in width. When considering the dynamic interaction between the active and passive components, we must be able to discern the relative volumes.
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Further field study may be helpful in identifying appropriate diagnostics of the different components of flow. Nighttime thermal data from THEMIS may also show differences in rock abundances across the flow that can be interpreted in terms of flow structure in areas where dust cover is not a problem. Here we have used a constant value. But, as noted elsewhere [e. In addition, it is likely that the material transferred often has different rheologic properties e. Results of ongoing investigations of these possibilities will appear elsewhere. When dimensional data on channels, levees, and stagnant zones are available, the apportioning of lava between active and passive components can be used to estimate the length scale or rate constant of this process.
This conclusion holds whether the processes of margin formation and degassing are included in the analysis or not. The observed thickening and widening of the flow is essentially what would be expected for a single coherent, isothermal, flow on a slightly inclined plane with minor topographic changes along the flow path.