Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Reconstruction of the collapse of the 'Azure Window' natural arch via
  photogrammetry   The Azure Window was a natural arch situated in the west coast of Gozo
(Maltese Archipelago) that collapsed in March 2017. We employ a Diver
Propulsion Vehicle-mounted camera system to capture data for the 3D-modelling
of this collapsed arch via photogrammetry. We demonstrate use of this method to
document complex underwater geomorphology spread across a large area, and draw
up a geomorphic assessment of the site and collapse event on the basis of this
3D-model. The methodology enables a reconstruction and understanding of the
collapse event. On account of the high-resolution attained, we are able to
cross-match the principal submerged components with their pre-collapse
location; this enables an understanding of the dynamics of the collapse,
confirmation of rock break-up along existing joints, and mapping the
distribution of the rock and debris from the collapse event. We conclude that
the key stages in the collapse of the Azure Window entailed erosion at the base
of the pillar, leading to the latter's collapse in the southwest direction,
breaking into two main sections that separated along the lithological boundary.
We also find clear evidence that separation of some sections of the pillar
followed pre-existing joints. The bridge collapsed vertically upon loss of
support from the pillar, breaking into two main components and many other
fragments. We also document further changes at the site post-collapse. We show
that this approach can be utilised to understand and characterise such events
even when significant time has elapsed since collapse, and rocks have already
undergone erosion and significant marine growth.

7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th