Geothermal Explosion at the 2014 Landslide-Covered Area of the Geyser Valley, Kamchatka, Russian Far East

Round 1

Reviewer 1 Report

This paper highlights the sources, consequences and in depth analysis of geothermal explosions in Geyser valley using state of art remote sensing techniques. The article is well presented, but rectifying a few grammatical and other technical aspects will add more value.

Authors are recommended to re-review for proof reading to avoid the following mistakes.

1. Line 22 in abstract needs revision as 'thermally active' seems inappropriate phrase.

2. Line 44 as well as 45 along with 97 need revision for grammer.

3. See the units of meter cube and place a space in line 101.

4. Abbreviated text should be placed once full form has been written/produced. Avoid using the Principal component analysis again and again once the short form has been introduced on line 245.

5. Authors forgot to place the full stop on line 263.

6. Likewise, extra space placed on line 324 needs correction/deletion..

7. Authors should add the results/ analysis of PCA in their results/discussion section too.

Author Response

Reviewer #1

Comments and Suggestions for Authors

This paper highlights the sources, consequences and in depth analysis of geothermal explosions in Geyser valley using state of art remote sensing techniques. The article is well presented, but rectifying a few grammatical and other technical aspects will add more value.

Authors are recommended to re-review for proof reading to avoid the following mistakes.

1. Line 22 in abstract needs revision as 'thermally active' seems inappropriate phrase.

Reply: we have rephrased this wording to “thermally active”

2. Line 44 as well as 45 along with 97 need revision for grammer.

Reply: we have rephrased this wording to  “experimental simulations”. We also rewrote the line 45 to “However, the sporadic appearance of geysers and thermal spots, and their disappear-ance and coverage by sediments, has been much less studied. Some systems may be dormant for years and become completely obscured, while others may reactivate again”. Also line 97 was rewritten to “Geysers can be monitored by …”.

3. See the units of meter cube and place a space in line 101.

Reply: We double checked the volume and heights and reworded the sentence now.

4. Abbreviated text should be placed once full form has been written/produced. Avoid using the Principal component analysis again and again once the short form has been introduced on line 245.

Reply: We agree and now replaced “Principal Component Analysis” by the abbreviation PCA

5. Authors forgot to place the full stop on line 263.

Reply: Accepted and changes made.

6. Likewise, extra space placed on line 324 needs correction/deletion..

Reply: Accepted and changes made.

7. Authors should add the results/ analysis of PCA in their results/discussion section too.

Reply: We appreciate this comment and made appropriate changes: In the results section we correct the description “To better visualise these subtle colour contrasts, we perform the PCA in figure 7b…” . We also added the PCA to the discussion section, where we now write “Our analysis of images (using the PCA) and comparison to thermal data shows that permeability and temperature is distributed heterogeneously at discrete sedimentary layers.”.

Author Response File: Author Response.docx

Reviewer 2 Report

General

Detailed photogrammetic and thermal image account of a geothermal field in Kamchatka. Excellent amount of data, combination of data is well done.

 

Detailed comments

Introduction – could precipitation also be a factor in the appearance disappearance of the fumaroles?

P3. L 97  geysers are monitored – phrasing

Figure  order of discussion in caption is reverse from a, b, c, d. --  last sentence of caption says red dot is the Malya Pechka – does this refer to the large red dot or to the many other red dots?  I assume it is the site of the large red dot (explosion crater) that was a geothermal vent 12 years earlier?

 

Line 350-351  lake was 20 m deep and former lake is now filled in. Is there quantitative evidence (DEM) that the sediment pile is also 20m thick?  With the fill up of the lake with sediment, its level will, rise, the dam will overflow and the ultimate lake level may have been lower. So what is the evidence that lake depth = equal to sediment thickness.

Line 387 Malya Pechka occurred …under a temporary lake on the depth about 10m (Fig 9b) – there are no a, b, c, d indications in the figure 9. Phrasing of the elevation or water depth is unclear.

Line 396 397  instead stating the overburden weight, it would be good to give the pressure at the site of Malya Pechka, e.g. how many bars pressure (probably around 3 or 4 bar). Knowing the pressure you can get the boiling temperature at that pressure from the steam tables (134-144 C at 3 or 4 bar).  You should also say what bulk sediment density to use for the pressure calculations for the 20m of water-bearing sediment.

 

The evolution of the Malya Pechka vent after burial is then as follows: although most vents today are at 94 C, the local boiling point at atmospheric pressure, it is likely that the boiling cools the fluid to this point and the deeper fluid could be hotter. So the buried MP vent may have had a higher water temperature. That water and the possible subterranean pool started to conduct heat upwards into the pile of sediment and rising fluids may have moved through the permeable space in the coarse grained layers,  creating small layers of hot geothermal fluid.  However, given the probably poor permeability of the lahar deposits, their temperature was probably similar to that of the surrounding sediment – there is much more sediment than water and the two will equilibrate towards the sediment temperature. One could envision a time progressive sequence of upwards flowing water that gets hotter and hotter over time, with similarly heated sediment in the surroundings, and once that has reached a temperature that is equal to the local boiling point: an explosion may occur after some steam accumulation has taken place.  The authors take the alternative view that thermal water percolates up, heats the surroundings and if there is a lowering of the water table pockets of thermal water become oversaturated in steam, steam accumulates and an explosion may occur.  The authors could try to map these two scenarios in a pressure temperature graph, possibly without exact values to show how the explosion may tale place.  It is important for hazard assessment if the explosion is caused by a lowering of the water table (that could be a signal to be aware) or as a gradual build up of a heated column of water over time, where it may be harder to predict when an explosion can be expected (although monitoring of water temperatures of seeps may be a good strategy for this model).

 

So my main suggestion for this paper that builds upon a beautiful data base of observations is to work out the explosion story in a slightly more quantitative way. The statement of overburden is 670 tons is not very useful information and should be recast in bars pressure of overburden, and then the total pressure at 20m depth is “weight of overburden” + 1 bar atmospheric pressure)

 

The question of the trigger for the geothermal explosion also relates to the question if the pressure at 20m depth is lithostatic (overburden weight, seems OK with the intercalation of impermeable layers) or hydrostatic – needs a fully connected network of water path ways, so lowering of the water table then lowers the hydrostatic pressure at depth. The authors express pressure as related to the 760 tons of rock overburden.

Author Response

Reviewer #2

Comments and Suggestions for Authors

 

General

 

Detailed photogrammetic and thermal image account of a geothermal field in Kamchatka. Excellent amount of data, combination of data is well done.

 

 

 

Detailed comments

 

Introduction – could precipitation also be a factor in the appearance disappearance of the fumaroles?

Reply: We appreciate this remark. However, we do not report on fumaroles. At geysers and hot pots, precipitation may affect the water temperatures indeed. We now also introduced precipitation in the introduction chapter.

P3. L 97  geysers are monitored – phrasing

Reply: Accepted and changes made. We changed the wording.

 

Figure  order of discussion in caption is reverse from a, b, c, d. --  last sentence of caption says red dot is the Malya Pechka – does this refer to the large red dot or to the many other red dots?  I assume it is the site of the large red dot (explosion crater) that was a geothermal vent 12 years earlier?

Reply: Accepted and changes made. We re-ordered the caption as suggested by the reviewer.

 

 

Line 350-351  lake was 20 m deep and former lake is now filled in. Is there quantitative evidence (DEM) that the sediment pile is also 20m thick?  With the fill up of the lake with sediment, its level will, rise, the dam will overflow and the ultimate lake level may have been lower. So what is the evidence that lake depth = equal to sediment thickness.

Reply: we agree and made the following changes, where we also added a sentence: “The depth of the lake and the height of the clastic sediments is approximately similar, which is why the map view (Figure 3) outline of the lake and the sedimentary cover are corresponding. This 20 m thick sedimentary cover is now traversed again by geothermal fluids. “

 

Line 387 Malya Pechka occurred …under a temporary lake on the depth about 10m (Fig 9b) – there are no a, b, c, d indications in the figure 9. Phrasing of the elevation or water depth is unclear.

Reply: We agree, our notations got lost in the submitted version. We now have added the indications a, b, c, d and e in the figure.

 

Line 396 397  instead stating the overburden weight, it would be good to give the pressure at the site of Malya Pechka, e.g. how many bars pressure (probably around 3 or 4 bar). Knowing the pressure you can get the boiling temperature at that pressure from the steam tables (134-144 C at 3 or 4 bar).  You should also say what bulk sediment density to use for the pressure calculations for the 20m of water-bearing sediment.

Reply: We appreciate this comment and made a number of relevant changes. We also provide the pressures at these depth levels, for both the hydrostatic and the lithostatic conditions. We now write: “As sedimentary layers accumulated 20 m of thick deposits on top of the original Malaya Pechka, the original Malaya Pechka vent is deeply buried beneath an estimated 670 tons of gravel and clay (5 meter diameter and 20 m height of sediment) [36], equivalent to ~30 kPa hydrostatic pressure, or ~50 kPa lithostatic pressure (assuming a bulk density of the sediment of 2,000 kg/m³). “

The evolution of the Malya Pechka vent after burial is then as follows: although most vents today are at 94 C, the local boiling point at atmospheric pressure, it is likely that the boiling cools the fluid to this point and the deeper fluid could be hotter. So the buried MP vent may have had a higher water temperature. That water and the possible subterranean pool started to conduct heat upwards into the pile of sediment and rising fluids may have moved through the permeable space in the coarse grained layers,  creating small layers of hot geothermal fluid.  However, given the probably poor permeability of the lahar deposits, their temperature was probably similar to that of the surrounding sediment – there is much more sediment than water and the two will equilibrate towards the sediment temperature. One could envision a time progressive sequence of upwards flowing water that gets hotter and hotter over time, with similarly heated sediment in the surroundings, and once that has reached a temperature that is equal to the local boiling point: an explosion may occur after some steam accumulation has taken place.  The authors take the alternative view that thermal water percolates up, heats the surroundings and if there is a lowering of the water table pockets of thermal water become oversaturated in steam, steam accumulates and an explosion may occur.  The authors could try to map these two scenarios in a pressure temperature graph, possibly without exact values to show how the explosion may tale place.  It is important for hazard assessment if the explosion is caused by a lowering of the water table (that could be a signal to be aware) or as a gradual build up of a heated column of water over time, where it may be harder to predict when an explosion can be expected (although monitoring of water temperatures of seeps may be a good strategy for this model).

Reply: We appreciate this very constructive comment and rewrote the conceptual model explanation accordingly, which now reads as follows: “Then two processes may have occurred, first a gradual heating of the covering deposits from below, and/or second, a gradual lowering of the sedimentary cover or groundwater table which was connected with gradual erosion of the dam composed by 2014 landslide deposits. Gradual upward heating may occur by conduction or fluid rise through the permeable space in coarse grained layers, creating small layers of hot geothermal fluids. If impermeable layers inhibit further thermal transfer, water heating might reach a boil-ing point, so that an explosion may occur (scenario (1) in Figure 10). We speculate that within a sedimentary package, a number of new pockets of thermal waters accumulated, and the boiling level newly established at a shallower depth level. Alternatively (or ad-ditionally), a lowering of the overburden causes pockets of thermal water to oversatu-rate in steam, so that an explosion may occur (scenario (2) in Figure 10). Therefore, the interplay between overburden pressure and heating up to a boiling point is critical to understand how the water reaches the boiling curve (Figure 10) and explosively ex-panded and triggered the geothermal explosion.”

So my main suggestion for this paper that builds upon a beautiful data base of observations is to work out the explosion story in a slightly more quantitative way. The statement of overburden is 670 tons is not very useful information and should be recast in bars pressure of overburden, and then the total pressure at 20m depth is “weight of overburden” + 1 bar atmospheric pressure)

Reply: We appreciate this constructive and positive feedback, and made changes as suggested. We also expanded the discussion about the overburden and boiling curve.  

The question of the trigger for the geothermal explosion also relates to the question if the pressure at 20m depth is lithostatic (overburden weight, seems OK with the intercalation of impermeable layers) or hydrostatic – needs a fully connected network of water path ways, so lowering of the water table then lowers the hydrostatic pressure at depth. The authors express pressure as related to the 760 tons of rock overburden.

Reply: we agree this is interesting to discuss. To further support our discussion we also added a very simple conceptual figure showing the boiling curve, where we can better illustrate the two scenarios discussed. If impermeable layers inhibit further thermal transfer, water heating might reach a boiling point, so that an explosion may occur (scenario (1) in Figure 10). We speculate that within a sedimentary package, a number of new pockets of thermal waters accumulated, and the boiling level newly established at a shallower depth level. Alternatively (or ad-ditionally), a lowering of the overburden causes pockets of thermal water to oversatu-rate in steam, so that an explosion may occur (scenario (2) in Figure 10). 

Author Response File: Author Response.docx