Review Reports

Round 1

Reviewer 1 Report

This is a very concise, convincing and interesting study. The authors very comprehensively describe a newly identified glacial erosional process, glacial ripping, that might be of considerable significance for our understanding of the glacial dynamics of former glaciers and ice sheets. I have observed several of the features described by the authors in deglaciated terrain in Scandinavia, but haven't connected the dots myself. I am very excited about the implications of this research!

The paper is very well written and systematic. I have only minor questions and comments to the manuscript (attached PDF).

I have a couple of (minor) overall concerns.

• The authors aptly call one of the main, driving processes "hydraulic jacking". The same wording was used a long time ago by Iken & Bindschadler (and others) for another process, where high subglacial water pressure increases ice flow velocity. This could be confusing for some readers that are invested in the glaciological literature. I think it would be worthwhile to adress and explain this potential confusion.
• I miss a direct comparison with the "null hypothesis", that is a comparison with the same type of rock but unaffected by glacial ripping just to make sure that the many features attributed to glacial ripping (dilation, brecciation, beam failure, fracture fill,...) are not a feature of the rock in general. I think there is a picture in figure 2b, showing unaffected Quartzite and somewhere in the text a general description of the rock type. However, a thorough close-up and description of this "null" rock in Fig 2b would be appreciated.

It is exciting that we can add another process sequence to the age old "glacial plucking and abrasion". Thank you for a very interesting, innovative and pedagogical contribution!

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for the supportive commentary.  We have been through and made corrections and changes in response to several points.

On the general point about hydraulic jacking, it is indeed the case that hydraulic jacking has been used previously to refer to ice-bed separation. But we refer in the Introduction of Line 31 to hydraulic jacking and the opening of fractures. So there should not be any confusion that we are dealing with hydraulic jacking in rock.

On the other general point about a null hypothesis, we acknowledge the value of that point. We tackle it by adding this statement about controls on line 201 

The precursor forms and in situ quartz-arenite bedrock (Figure 2b) act as our controls for the identification of damage and disruption.

On the detailed points

Line 45 No change. The text seems clear to us.

Line 78. Assynt changed to NW Scotland.

Line 144. Table 1 is about the presence/absence of marker features. We can't deal with frequency.

Line 202 We have added British National Grid reference to the first mention. The difference between 8 and 6 figure references is in 10 m and 100 m grid location.

Line 268. The point about what the rock usually looks like is a good one. So we included mention of Figure 2b in that statement above on controls.

Line 344. We have added exposed in a gravel pit.

Line 429 Good point about YD frost weathering. We cover that in Line 435 where we point out that there are many undamaged surfaces.

Line 439. We are explicit that hydraulic jacking is operating in the rock.

Line 563 That modelling of hydraulic jacking is underway in Sweden.

Table 2 probably should have some Russian examples. There is some very deep seated glacitectonic disturbance reported in permafrost. But, as the reviewer points out, this literature is hard to access. 

Reviewer 2 Report

My sole comment is that is an especially excellent paper.  the best i have reviewed in a decade.

Author Response

High praise indeed!

Much appreciated.