I I ntroduction: ntroduction: This study is concerned with the effect of temperature This study is concerned with the effect of temperature on the topography of the near on the topography of the near - - equatorial trough of Coprates equatorial trough of Coprates Chasma. Chasma. One of the outstanding questions concerning the evolution of the Valles One of the outstanding questions concerning the evolution of the Valles Marineris troughs, and of equatorial landforms Marineris troughs, and of equatorial landforms in general, concerns the in general, concerns the possible presence of ground ice and its role in landscape evolution possible presence of ground ice and its role in landscape evolution [1 [1 - - 3] 3] . . Over geologic time, surface Over geologic time, surface heat (by its influence on the stability and heat (by its influence on the stability and rheology of ice rheology of ice - - rich frozen ground) may be a factor in the evolution and rich frozen ground) may be a factor in the evolution and morphology morphology of the trough walls by controlling the distribution of ground of the trough walls by controlling the distribution of ground ice ice [1 [1 - - 4] 4] . This study aims to determine whether the expected surf . This study aims to determine whether the expected surf ace ace temperature difference between the north and south walls of Coprates temperature difference between the north and south walls of Coprates Chasma, results in a measurable difference in trough wa Chasma, results in a measurable difference in trough wa ll stability, slope ll stability, slope angle, and surface roughness. angle, and surface roughness. Figure 1. Coprates Chasma with 247 Profiles. Figure 1. Coprates Chasma with 247 Profiles. Discussion: Discussion: To determine whet To determine whet her temperature is a factor, systematic her temperature is a factor, systematic variations in topographic parameters with predicted mean annual variations in topographic parameters with predicted mean annual surface temperature, loc surface temperature, loc ation (latitude and longitude), and trough ation (latitude and longitude), and trough geometry (wall height, rim elevation, and trough width) were examined, geometry (wall height, rim elevation, and trough width) were examined, as were differ as were differ ences in topographic parameters (slope angle, curvature, ences in topographic parameters (slope angle, curvature, and surface area ratio) between the north and south walls of Coprates and surface area ratio) between the north and south walls of Coprates Chasma. Slope angles, surface roughness, and other derivatives were Chasma. Slope angles, surface roughness, and other derivatives were calculated from the 1/64 degree MOLA gridded elevation data calculated from the 1/64 degree MOLA gridded elevation data set. 247 set. 247 profiles were drawn across the trough ( profiles were drawn across the trough ( Fig. 1 Fig. 1 , , Fig. 2 Fig. 2 ), extracting ), extracting topographic data, which was related to surface tempe topographic data, which was related to surface tempe rature, location, rature, location, and trough geometry ( and trough geometry ( Fig. 3 Fig. 3 , , Fig. 4 Fig. 4 , , Fig. 5 Fig. 5 ). Comparisons of differences ). Comparisons of differences in topographic and other parameters b in topographic and other parameters b etween the north and south walls etween the north and south walls were made ( were made ( Fig. 4 Fig. 4 , , Fig. 5 Fig. 5 ). ). Figure 2. Valid Points for Analysis on Coprates Figure 2. Valid Points for Analysis on Coprates Chasma Profile 2 Chasma Profile 2 00. 00. Vertical exaggeration = Vertical exaggeration = 6 6 x; profile aspect = x; profile aspect = 1 1 87.2º (north 87.2º (north wall) / wall) / 7.2º (south wall); 7.2º (south wall); points points selected as valid have slope aspects selected as valid have slope aspects within within ±60º of profile aspect, and ±60º of profile aspect, and slope angles slope angles steeper than 5º. steeper than 5º. Fig. 3 Fig. 3 shows the estimated average annual surface temperature along shows the estimated average annual surface temperature along Coprates Chasma profile number 200, showing the colder nor Coprates Chasma profile number 200, showing the colder nor th th (poleward) walls. This is representative for most of the 247 profiles. (poleward) walls. This is representative for most of the 247 profiles. Predicted mean annual surface temperature varies Predicted mean annual surface temperature varies from from 202 202 - - 212 K 212 K along the north wall and from 216 along the north wall and from 216 - - 218 K on the south wall ( 218 K on the south wall ( Fig. 4 Fig. 4 ). The ). The temperature difference between the two walls temperature difference between the two walls varies from ~7.5 K at the varies from ~7.5 K at the western end of the trough to ~11.5 K at the eastern end, and averages western end of the trough to ~11.5 K at the eastern end, and averages 9.7 K. The north and south walls 9.7 K. The north and south walls have average slope angles of ~22.4º have average slope angles of ~22.4º and ~21.1º respectively, the north wall being steeper by ~1.3º ( and ~21.1º respectively, the north wall being steeper by ~1.3º ( Fig. 5 Fig. 5 ). ). B B e e cause the ranges of slope angle are similar for both walls, but the cause the ranges of slope angle are similar for both walls, but the te te m m perature range differs, slope angle decreases as a function of te perature range differs, slope angle decreases as a function of te m- m- perature at ~6° of slope per K for the south wall, compared with ~1° per perature at ~6° of slope per K for the south wall, compared with ~1° per K for the north wall. K for the north wall. Figure 3. Temperature along C Figure 3. Temperature along C oprates Chasma oprates Chasma Profile 200. Profile 200. Elevation profile vertical exaggeration = Elevation profile vertical exaggeration = 5 5 x. x. Figure 4. Surface Temperature vs. Figure 4. Surface Temperature vs. Longitude. Longitude. Figure 5. Slope Angle vs. Longitude. Figure 5. Slope Angle vs. Longitude. Conclusions: Conclusions: The difference in slope angle between the two walls for The difference in slope angle between the two walls for all the profiles measured correlates significantly with the surface te all the profiles measured correlates significantly with the surface te m- m- perature difference between the two walls. Correlations of slope angle perature difference between the two walls. Correlations of slope angle and slope angle difference with location or trough geomet and slope angle difference with location or trough geomet ry factors are ry factors are insignificant. In addition, the pattern of slope angle variation along the insignificant. In addition, the pattern of slope angle variation along the trough is not associated with known or trough is not associated with known or suspected faulting patterns suspected faulting patterns [4, [4, 5] 5] . Furthermore, the slope angle asymmetry is not due to an asymmetric . Furthermore, the slope angle asymmetry is not due to an asymmetric graben geometry for the graben geometry for the trough as there is no tilt on the floor across the trough as there is no tilt on the floor across the trough ( trough ( Fig. 6 Fig. 6 , , Fig. 7 Fig. 7 ). ). Figure 6. Elevations of Coprates Floor and Surround Figure 6. Elevations of Coprates Floor and Surround ing Plateaus. ing Plateaus. Rock mass strength differences between the walls are unlikely given Rock mass strength differences between the walls are unlikely given that layering in the walls appears to be horiz that layering in the walls appears to be horiz ontal ontal [4 [4 - - 8] 8] . All these results . All these results suggest that it is temperature differentials, rather than location or trough suggest that it is temperature differentials, rather than location or trough geometric factors th geometric factors th at have produced the systematic, trough at have produced the systematic, trough - - averaged averaged difference in slope angle between the two walls. However, difference in slope angle between the two walls. However, Fig. 9 Fig. 9 when when taken in context with taken in context with [6] [6] shows that rock mass strength can not concl shows that rock mass strength can not concl u- u- sively be ruled out as a factor. sively be ruled out as a factor. Figure 7. Trough Wall Bottom Elevations for North and South Walls. Figure 7. Trough Wall Bottom Elevations for North and South Walls. The results are consistent The results are consistent with a differential presence and depth of with a differential presence and depth of ground ice within the north and south walls. The depth to the ice table is ground ice within the north and south walls. The depth to the ice table is shallower shallower underneath the north wall by a few tens to ~100 meters, and underneath the north wall by a few tens to ~100 meters, and the cryosphere deeper by ~1 km ( the cryosphere deeper by ~1 km ( Fig. 8 Fig. 8 ; ; [3] [3] ); the ice table is also pr ); the ice table is also pr e- e- dicted to be colder underneath the north wall. Given the known increase dicted to be colder underneath the north wall. Given the known increase in the strength and resistance of ice to deformation wit in the strength and resistance of ice to deformation wit h decreasing h decreasing te te m m perature, the north wall is considered to be more stable and perature, the north wall is considered to be more stable and stronger, and therefore can maintain steeper slope angles on averag stronger, and therefore can maintain steeper slope angles on averag e e than the south wall. than the south wall. Figure 8. Coprates Chasma Profile 200 with Hypothetical Cryosphere. Figure 8. Coprates Chasma Profile 200 with Hypothetical Cryosphere. Calculated using n Calculated using n ominal thermal parameters from ominal thermal parameters from [3] [3] ; ; vertical exaggeration = 6x. vertical exaggeration = 6x. Figure 9. Coprates Chasma Trough Wall Height Figure 9. Coprates Chasma Trough Wall Height vs. Slope Angle vs. Slope Angle Superimposed on the Results of Superimposed on the Results of [6] [6] . . References: References: [1] [1] Carr M. H. (1996) Carr M. H. (1996) Water on Mars Water on Mars . . [2] [2] Squyres et al. Squyres et al. (1992). In: (1992). In: Mars Mars . . [3] [3] Clifford S. M. (1993) Clifford S. M. (1993) JGR JGR , 98/E6, 10,973 , 98/E6, 10,973 - - 11,016. 11,016. [4] [4] Lucchitta et al. (1992). Lucchitta et al. (1992). In: In: Mars Mars . . [5] [5] Peulvast et al. Peulvast et al. (2001) (2001) Geomo Geomo r- r- phology phology , 37/3 , 37/3 - - 4, 329 4, 329 - - 352. 352. [6] [6] Schultz (2002) Schultz (2002) GRL GRL , 29/19. , 29/19. [7] [7] Malin M. C. Malin M. C. and Edgett K. S. (2001) and Edgett K. S. (2001) JGR JGR , 106/E10, 23,429 , 106/E10, 23,429 - - 23,570 23,570 . . [8] [8] Malin et al. Malin et al. (1998) (1998) Science Science , 279, 1,681 , 279, 1,681 - - 1,685. 1,685. POSSIBLE TEMPERATURE POSSIBLE TEMPERATURE - - RELATED DIFFERENCES IN SLOPE ANGLE RELATED DIFFERENCES IN SLOPE ANGLE BETWEEN THE NORTH AND SOUTH WALLS OF COPRATES CHASMA, MARS BETWEEN THE NORTH AND SOUTH WALLS OF COPRATES CHASMA, MARS J. A. Jernsle J. A. Jernsle tten, University of Bergen, Norway, http://joern.jernsletten.name/, [email protected] tten, University of Bergen, Norway, http://joern.jernsletten.name/, [email protected]
Jernsletten_2004_LPSC_35_1495_poster
Aug 17, 2015
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
IIntroduction:ntroduction: This study is concerned with the effect of temperature This study is concerned with the effect of temperature
on the topography of the nearon the topography of the near--equatorial trough of Copratesequatorial trough of Coprates Chasma. Chasma.
One of the outstanding questions concerning the evolution of the Valles One of the outstanding questions concerning the evolution of the Valles
Marineris troughs, and of equatorial landforms Marineris troughs, and of equatorial landforms in general, concerns the in general, concerns the
possible presence of ground ice and its role in landscape evolution possible presence of ground ice and its role in landscape evolution [1[1--3]3]. .
Over geologic time, surfaceOver geologic time, surface heat (by its influence on the stability and heat (by its influence on the stability and
rheology of icerheology of ice--rich frozen ground) may be a factor in the evolution and rich frozen ground) may be a factor in the evolution and
morphologymorphology of the trough walls by controlling the distribution of ground of the trough walls by controlling the distribution of ground
ice ice [1[1--4]4]. This study aims to determine whether the expected surf. This study aims to determine whether the expected surface ace
temperature difference between the north and south walls of Coprates temperature difference between the north and south walls of Coprates
Chasma, results in a measurable difference in trough waChasma, results in a measurable difference in trough wall stability, slope ll stability, slope
angle, and surface roughness.angle, and surface roughness.
Figure 1. Coprates Chasma with 247 Profiles.Figure 1. Coprates Chasma with 247 Profiles.
Discussion:Discussion: To determine whet To determine whether temperature is a factor, systematic her temperature is a factor, systematic
variations in topographic parameters with predicted mean annual variations in topographic parameters with predicted mean annual
surface temperature, locsurface temperature, location (latitude and longitude), and trough ation (latitude and longitude), and trough
geometry (wall height, rim elevation, and trough width) were examined, geometry (wall height, rim elevation, and trough width) were examined,
as were differas were differences in topographic parameters (slope angle, curvature, ences in topographic parameters (slope angle, curvature,
and surface area ratio) between the north and south walls of Coprates and surface area ratio) between the north and south walls of Coprates
Chasma. Slope angles, surface roughness, and other derivatives were Chasma. Slope angles, surface roughness, and other derivatives were
calculated from the 1/64 degree MOLA gridded elevation datacalculated from the 1/64 degree MOLA gridded elevation dataset. 247 set. 247
profiles were drawn across the trough (profiles were drawn across the trough (Fig. 1Fig. 1, , Fig. 2Fig. 2), extracting ), extracting
topographic data, which was related to surface tempetopographic data, which was related to surface temperature, location, rature, location,
and trough geometry (and trough geometry (Fig. 3Fig. 3, , Fig. 4Fig. 4, , Fig. 5Fig. 5). Comparisons of differences ). Comparisons of differences
in topographic and other parameters bin topographic and other parameters between the north and south walls etween the north and south walls
were made (were made (Fig. 4Fig. 4, , Fig. 5Fig. 5).).
Figure 2. Valid Points for Analysis on CopratesFigure 2. Valid Points for Analysis on Coprates Chasma Profile 2Chasma Profile 200.00.
Vertical exaggeration = Vertical exaggeration = 66x; profile aspect =x; profile aspect = 1 187.2º (north87.2º (north wall) /wall) /
7.2º (south wall); 7.2º (south wall); pointspoints selected as valid have slope aspectsselected as valid have slope aspects
withinwithin ±60º of profile aspect, and±60º of profile aspect, and slope anglesslope angles steeper than 5º.steeper than 5º.
Fig. 3Fig. 3 shows the estimated average annual surface temperature along shows the estimated average annual surface temperature along
Coprates Chasma profile number 200, showing the colder norCoprates Chasma profile number 200, showing the colder north th
(poleward) walls. This is representative for most of the 247 profiles.(poleward) walls. This is representative for most of the 247 profiles.
Predicted mean annual surface temperature varies Predicted mean annual surface temperature varies fromfrom 202 202--212 K 212 K
along the north wall and from 216along the north wall and from 216--218 K on the south wall (218 K on the south wall (Fig. 4Fig. 4). The ). The
temperature difference between the two walls temperature difference between the two walls varies from ~7.5 K at the varies from ~7.5 K at the
western end of the trough to ~11.5 K at the eastern end, and averages western end of the trough to ~11.5 K at the eastern end, and averages
9.7 K. The north and south walls9.7 K. The north and south walls have average slope angles of ~22.4º have average slope angles of ~22.4º
and ~21.1º respectively, the north wall being steeper by ~1.3º (and ~21.1º respectively, the north wall being steeper by ~1.3º (Fig. 5Fig. 5). ).
BBeecause the ranges of slope angle are similar for both walls, but the cause the ranges of slope angle are similar for both walls, but the
tetemmperature range differs, slope angle decreases as a function of teperature range differs, slope angle decreases as a function of tem-m-
perature at ~6° of slope per K for the south wall, compared with ~1° per perature at ~6° of slope per K for the south wall, compared with ~1° per
K for the north wall.K for the north wall.
Figure 3. Temperature along CFigure 3. Temperature along Coprates Chasmaoprates Chasma Profile 200.Profile 200.
Elevation profile vertical exaggeration = Elevation profile vertical exaggeration = 55x.x.
Figure 4. Surface Temperature vs. Figure 4. Surface Temperature vs. Longitude.Longitude.
Figure 5. Slope Angle vs. Longitude.Figure 5. Slope Angle vs. Longitude.
Conclusions: Conclusions: The difference in slope angle between the two walls for The difference in slope angle between the two walls for
all the profiles measured correlates significantly with the surface teall the profiles measured correlates significantly with the surface tem-m-
perature difference between the two walls. Correlations of slope angle perature difference between the two walls. Correlations of slope angle
and slope angle difference with location or trough geometand slope angle difference with location or trough geometry factors are ry factors are
insignificant. In addition, the pattern of slope angle variation along the insignificant. In addition, the pattern of slope angle variation along the
trough is not associated with known ortrough is not associated with known or suspected faulting patterns suspected faulting patterns [4, [4,
5]5]. Furthermore, the slope angle asymmetry is not due to an asymmetric . Furthermore, the slope angle asymmetry is not due to an asymmetric
graben geometry for the graben geometry for the trough as there is no tilt on the floor across the trough as there is no tilt on the floor across the
trough (trough (Fig. 6Fig. 6, , Fig. 7Fig. 7).).
Figure 6. Elevations of Coprates Floor and SurroundFigure 6. Elevations of Coprates Floor and Surrounding Plateaus.ing Plateaus.
Rock mass strength differences between the walls are unlikely given Rock mass strength differences between the walls are unlikely given
that layering in the walls appears to be horizthat layering in the walls appears to be horizontal ontal [4[4--8]8]. All these results . All these results
suggest that it is temperature differentials, rather than location or trough suggest that it is temperature differentials, rather than location or trough
geometric factors thgeometric factors that have produced the systematic, troughat have produced the systematic, trough--averaged averaged
difference in slope angle between the two walls. However, difference in slope angle between the two walls. However, Fig. 9Fig. 9 when when
taken in context with taken in context with [6][6] shows that rock mass strength can not concl shows that rock mass strength can not conclu-u-
sively be ruled out as a factor.sively be ruled out as a factor.
Figure 7. Trough Wall Bottom Elevations for North and South Walls.Figure 7. Trough Wall Bottom Elevations for North and South Walls.
The results are consistentThe results are consistent with a differential presence and depth of with a differential presence and depth of
ground ice within the north and south walls. The depth to the ice table is ground ice within the north and south walls. The depth to the ice table is
shallower shallower underneath the north wall by a few tens to ~100 meters, and underneath the north wall by a few tens to ~100 meters, and
the cryosphere deeper by ~1 km (the cryosphere deeper by ~1 km (Fig. 8Fig. 8; ; [3][3]); the ice table is also pr); the ice table is also pre-e-
dicted to be colder underneath the north wall. Given the known increase dicted to be colder underneath the north wall. Given the known increase
in the strength and resistance of ice to deformation witin the strength and resistance of ice to deformation with decreasing h decreasing
tetemmperature, the north wall is considered to be more stable and perature, the north wall is considered to be more stable and
stronger, and therefore can maintain steeper slope angles on averagstronger, and therefore can maintain steeper slope angles on average e
than the south wall.than the south wall.
Figure 8. Coprates Chasma Profile 200 with Hypothetical Cryosphere.Figure 8. Coprates Chasma Profile 200 with Hypothetical Cryosphere.
Calculated using n Calculated using nominal thermal parameters from ominal thermal parameters from [3][3];;
vertical exaggeration = 6x. vertical exaggeration = 6x.
Figure 9. Coprates Chasma Trough Wall Height Figure 9. Coprates Chasma Trough Wall Height vs. Slope Angle vs. Slope Angle
Superimposed on the Results of Superimposed on the Results of [6][6]..
References:References: [1][1] Carr M. H. (1996) Carr M. H. (1996) Water on MarsWater on Mars. . [2][2] Squyres et al. Squyres et al.
(1992). In: (1992). In: MarsMars. . [3][3] Clifford S. M. (1993) Clifford S. M. (1993) JGRJGR, 98/E6, 10,973, 98/E6, 10,973--11,016. 11,016.
[4][4] Lucchitta et al. (1992). Lucchitta et al. (1992). In: In: MarsMars. . [5][5] Peulvast et al. Peulvast et al. (2001) (2001) GeomoGeomor-r-
phologyphology, 37/3, 37/3--4, 3294, 329--352. 352. [6][6] Schultz (2002) Schultz (2002) GRLGRL, 29/19. , 29/19. [7][7] Malin M. C. Malin M. C.
and Edgett K. S. (2001) and Edgett K. S. (2001) JGRJGR, 106/E10, 23,429, 106/E10, 23,429--23,57023,570. . [8][8] Malin et al. Malin et al.
(1998) (1998) ScienceScience, 279, 1,681, 279, 1,681--1,685.1,685.
POSSIBLE TEMPERATUREPOSSIBLE TEMPERATURE--RELATED DIFFERENCES IN SLOPE ANGLERELATED DIFFERENCES IN SLOPE ANGLE
BETWEEN THE NORTH AND SOUTH WALLS OF COPRATES CHASMA, MARSBETWEEN THE NORTH AND SOUTH WALLS OF COPRATES CHASMA, MARS J. A. JernsleJ. A. Jernsletten, University of Bergen, Norway, http://joern.jernsletten.name/, [email protected], University of Bergen, Norway, http://joern.jernsletten.name/, [email protected]