a15_v_bw_o_n (AS15-90-12196)
Note the mini-landslide of lunar soil produced by the boot print near bottom/center. An extract from the informative ALSJ follows:
The footprints Dave made after dismounting are above center on the far side of the Rover tracks. Jim's are on the near side.
Journal Contributor Gary Swearingen calls attention to the mini-landslides triggered by Jim's footsteps as he made his way down from the original Rover parking spot. A detail focuses on the sequence of footprints and suggests that, initially, Jim put one foot in front of the other, staying on a single level but, eventually, stepped down with his left boot and had his feet on different levels. Swearingen calls particular attention to the mini-landslide associated with the bootprints below the center of the image. The soil in that slides looks like it may have moved as a unit.
In response to a January 2006 e-mail about the mini-landslides, Apollo soil mechanics investigator David Carrier wrote, "You have started the New Year off with an interesting question!"
"Actually, our soil mechanics team noticed the same bootprints: see Figure 7-12 (AS15-90-12197) on p. 7-12 of the Apollo 15 Preliminary Science Report. They were discussed briefly in a section of the report concerning slope stability, pp. 7-9 to 7-12: 'A preliminary study of the 70- and 500-mm photography available thus far has been made for evidence of slope instability and past slope failures. No indication exist of previous deep-seated slope failures of the type that have been suggested by Lunar Orbiter photos of some areas of the Moon. The near-surface zones of some slopes may be near incipient failure, however. The foreground of figure 7-12 shows failure under footprints as one of the astronauts traversed the slope in the vicinity of station 6A. Detailed analysis of conditions in this area must await more precise determination of the slope angle, which is estimated to be 10 deg to 20 deg.' And the caption of Figure 7-12 reads: 'Incipient slope failure as indicated by slipping out of soil beneath astronauts' feet.'"
"As I recall, we did not pursue a more detailed analysis."
"The photo in Figure 7-12 of the report is identified as AS15-90-12197 (and, because it is part of a panoramic sequence) it would be interesting to (use adjacent images) under a stereoscope - which I no longer have! - and get a somewhat distorted stereoscopic view. It would certainly help with estimating the slope angle."
Carrier continues, "My impression is that there is a slight break in the slope near the closest LRV track. That is, the LRV drove along an area that was slightly flatter, and that immediately downslope from the nearest track, there is a slight local steepening. Then, when Jim Irwin walked along the track, straddling it, one foot was on the flatter area - which was pretty soft anyhow, as you can see from the depth of the bootprints - and one foot was on the top - or 'shoulder' - of the slightly steeper slope. So, his downhill bootprints caused the soil to shear and slide outward, rather than simply compress the soil downward. I agree with you that the downhill boot would be somewhat heavier than the uphill. As for the difference between the two closest downhill bootprints, it might be due to: (1) Simply a slight difference in where he placed his boot with respect to the top of the local slope; or (2) That he rotated his boot downhill in the closest bootprint, causing some fines to move over the blocky material, making it look smooth; or a combination of both."
a15_v_bw_o_n (AS15-90-12196)
Note the mini-landslide of lunar soil produced by the boot print near bottom/center. An extract from the informative ALSJ follows:
The footprints Dave made after dismounting are above center on the far side of the Rover tracks. Jim's are on the near side.
Journal Contributor Gary Swearingen calls attention to the mini-landslides triggered by Jim's footsteps as he made his way down from the original Rover parking spot. A detail focuses on the sequence of footprints and suggests that, initially, Jim put one foot in front of the other, staying on a single level but, eventually, stepped down with his left boot and had his feet on different levels. Swearingen calls particular attention to the mini-landslide associated with the bootprints below the center of the image. The soil in that slides looks like it may have moved as a unit.
In response to a January 2006 e-mail about the mini-landslides, Apollo soil mechanics investigator David Carrier wrote, "You have started the New Year off with an interesting question!"
"Actually, our soil mechanics team noticed the same bootprints: see Figure 7-12 (AS15-90-12197) on p. 7-12 of the Apollo 15 Preliminary Science Report. They were discussed briefly in a section of the report concerning slope stability, pp. 7-9 to 7-12: 'A preliminary study of the 70- and 500-mm photography available thus far has been made for evidence of slope instability and past slope failures. No indication exist of previous deep-seated slope failures of the type that have been suggested by Lunar Orbiter photos of some areas of the Moon. The near-surface zones of some slopes may be near incipient failure, however. The foreground of figure 7-12 shows failure under footprints as one of the astronauts traversed the slope in the vicinity of station 6A. Detailed analysis of conditions in this area must await more precise determination of the slope angle, which is estimated to be 10 deg to 20 deg.' And the caption of Figure 7-12 reads: 'Incipient slope failure as indicated by slipping out of soil beneath astronauts' feet.'"
"As I recall, we did not pursue a more detailed analysis."
"The photo in Figure 7-12 of the report is identified as AS15-90-12197 (and, because it is part of a panoramic sequence) it would be interesting to (use adjacent images) under a stereoscope - which I no longer have! - and get a somewhat distorted stereoscopic view. It would certainly help with estimating the slope angle."
Carrier continues, "My impression is that there is a slight break in the slope near the closest LRV track. That is, the LRV drove along an area that was slightly flatter, and that immediately downslope from the nearest track, there is a slight local steepening. Then, when Jim Irwin walked along the track, straddling it, one foot was on the flatter area - which was pretty soft anyhow, as you can see from the depth of the bootprints - and one foot was on the top - or 'shoulder' - of the slightly steeper slope. So, his downhill bootprints caused the soil to shear and slide outward, rather than simply compress the soil downward. I agree with you that the downhill boot would be somewhat heavier than the uphill. As for the difference between the two closest downhill bootprints, it might be due to: (1) Simply a slight difference in where he placed his boot with respect to the top of the local slope; or (2) That he rotated his boot downhill in the closest bootprint, causing some fines to move over the blocky material, making it look smooth; or a combination of both."