Dear Brighenti et al., I am recommending a second review of your article following implementation of the suggestions/corrections listed by both reviewers.

I look forward to receiving your revised manuscript.

All the best,
Michelle Parks

Many thanks for submitting your revised manuscript. Following the feedback from the reviewers I am recommending publication following minor revisions and a final review by the editor.

Please implement the corrections indicated by both reviewers and please consider the suggestions from referee 3 listed below:

"Dear authors,
I carefully reviewed your paper and I greatly appreciate your work and your contribute to the knowledge on geological hazards studied through drone surveys and Structure from Motion techniques. I think your research is of great interest for the scientific community, but I would improve its structure (especially on Methodology and Results, which I believe are not explained thoroughly), and the clarity of some concepts (I think that by rephrasing some parts of the manuscript, the reader would be helped in better understanding the process that has brought you to your results and the value of your data)."

All the best,
Michelle Parks

Please implement the corrections stated below - this will be the final opportunity to correct the manuscript.

lines 11-12 please reword - this does not currently make sense.
line 13 "of natural hazards"
lines 13-15 change "The use of Unmanned Aerial Vehicles (UAVs) in contexts of natural hazard presents three main steps for risk assessment and monitoring: pre-post event data acquisition, emergency support and monitoring." to "The use of Unmanned Aerial Vehicles (UAVs) in relation to observation of natural hazards, encompasses three main stages: pre-post event data acquisition, monitoring and risk assessment."
line 16 “to infrastructure within a range ...”
line 17 change "clues of" to "precursors to" also change "are the uplift and the development of structural features with dimensions ranged from centimetre to decimetre." to "are uplift and the development of structural features with dimensions ranging from centimetres to decimetres."
line 18 change to "Here we present a methodology for monitoring deformation processes
that may be precursory to paroxysmal events at the Santa Barbara mud volcano. This methodology is based on i) the data collection, ii) the Structure from Motion (SfM) processing chain and iii) the M3C2-PM algorithm for the comparison between point clouds and uncertainty analysis with a statistical approach. The objective of this methodology is to detect precursory activity by monitoring deformation processes with centimetre scale precision and a temporal frequency of 1 - 2 months."
line 25 - "has allowed the generation of"
line 38 - for 3D reconstruction
line 43 - change "is spreading" to "is becoming more widely used"
line 46 - important to study catastrophic natural events
line 46 - remove subsidence as an example - this alone is not a catastrophic event
line 48 - change allow to acquire to "enable the acquisition of"
line 78 - change to "At several mud volcanoes (e.g. Ayaz-Akhtarma and Khara Zira Island mud volcanoes in Indonesia), certain geomorphic/structural features have been observed within the year preceding a paroxysmal event (Antonelli et al., 2014; Madonia et al., 2011)."
line 95 - reword - this does not make sense – do you mean they extend outside the mapped limits of the volcano?
line 97 - in 2002 and 2008
line 140 - reduced to approximately 4 cm
In section 2.4 remove unnecessary paragraph indents and reword the repeated use of "After that, after this etc" - for example to following this ...
line 230 - The next step ...
line 234 - reword "the best is ..." this is not very scientific.
line 243 "Once the ..." and "in order to determine the changes between them"
line 315 - is to detect significant deformation ...
line 316 - this deformation
lines 324-325 - reword
line 360 - The first is ...
line 383 - reword first sentence
line 386 - small area ... or in a larger region ...
line 391 - This monitoring technique is a useful tool ...
line 395 - uplift can occur ...
line 397 - In hazard management ...
line 403 - development of ...
line 416 - and ii) …

Please just reword the first sentence: All active geological processes generally determine effects on the ground surfaces such as uplift, subsidence and shear lineaments.

I would suggest "Active geological processes often generate a ground surface response such as uplift, subsidence and faulting/fracturing."