Using 3D laser scanning to detect structural changes in salt and ice caves

Author:Tommaso Santagata

Terrestrial Laser Scanning (TLS) has been used for underground surveys for more than a decade, and it is increasingly being used in the a exploration and research in caves. Tommaso Santagata from the virtual geographic agencyVigeahas recently usedLeica Geosystems激光扫描解决方案in two cave surveys: an investigation of the morphological (form and structure) changes in the Lechuza salt cave in Chile and in the natural well ice cave in Italy.

Santagata解释了如何在洞穴环境中详细扫描可以洞悉洞穴环境中的物理变化，但“尽管大多数发生在洞穴中的过程相对较慢，但有些过程可能很快，例如洪水引起的侵蚀。这些地质变化可以通过陆地激光扫描调查来监测，并通过比较“前后” 3D模型来衡量。这是一个有趣的工具，可以随着时间的推移进行比较，因此越来越多地用于气候变化的研究。”

衡量由Lechuza洞穴洪水引起的变化（Cordillera de la Sal）

关to the Chilean village of San Pedro de Atacama is an important cave, composed of Oligo-Miocene mineral deposit rocks, known as Cordillera de la Sal. Two surveys carried out in 2015 and 2018 allowed Santagata’s team to verify and measure small topographical changes in the cave due to a flood in 2017, which caused the river in the cave to flow and dissolve a measurable amount of halite - commonly known as rock salt.

In 2015, a complete 3D survey of the cave was organised byLa Venta Esplorazioni Geograficheand the Commissione Grotte Eugenio Boegan of Trieste. The team used a Leica HDS7000 phase-based laser scanner to perform about 50 scans. In 2018, the La Venta team, in collaboration with the University of Bologna used aLeica ScanStation P40执行68扫描,其中包括约200 -米苏rveyed in the external canyon upstream of the cave as part of the research project “Reading the salt caves of Atacama” supported by the National Geographic Society.

Lechuza data obtained in point cloud file format was subsequently analysed to identify areas where changes had occurred. Santagata explains, “Since very limited variations were found, it was necessary to recognise points in common and position the point clouds in the same origin and orientation to make comparisons. In at least three areas of the cave, collapses from the ceiling and erosion on the floor were recognised and digitised to obtain detailed sections of these parts of the cave. The comparison between these two surveys has shown that in this case, it was possible to accurately document the areas where detachments or torrential erosion occurred.”

天然井岩石洞穴监测项目：测量冰崩溃

第二项研究涉及在意大利白云岩中最深，最庞大的洞穴之一，这是Cenote深渊的地下冰矿床。这座280米深的冰洞是在1994年因扇形，森恩斯和布拉伊斯地区公园突然排空的小湖而打开后发现的。该洞穴的垂直入口包括一个巨大的130米厚分层冰矿床；在充满冰的入口部分的下限，A轴打开 - 无冰和165米深 - 通向一个由洞穴岩石冰川占据的圆顶形腔室。

激光扫描2015年进行的调查,2016年nd in 2018 allowed Santagata’s team to estimate variations due to collapses and acquire data for a complete monitoring project. The first expedition in October 2015 included a complete 3D laser scan survey of the final chamber using a HDS7000 phase-based laser scanner. This survey has provided the detailed volume of the chamber (420,000 m³) as well as a first record of the position of the ice masses hanging from the ceiling and of the rock glacier at the bottom. During this expedition and in subsequent ones in 2016 and 2018, other parts of the cave were 3D scanned using a ScanStation P40.

Santagata explains, “Due to the ice filling in some passages in the following years, it was not possible to repeat the survey of the final chamber (this will be a goal for future expeditions). However, the data acquired in these years in the upper part of the cave has allowed us to study the changes that have taken place in the first two rooms near the entrance. In particular, a collapse was highlighted in one area, which led to the enlargement of a passage occurred after 2016. This area was 3D scanned before and after the collapse and the acquired data allowed us to verify the detachment and quantify the volume of rocks collapsed.”

Point clouds were compared using two different methods: firstly we ran a quick comparison between the two datasets in order to understand where to focus our more detailed analysis. Secondly, we extracted several ‘slices’ of the areas of interest. We exported these areas for a complete digitisation, to have a better estimation of the volume of rock collapsed, about 61m³.”

正在进行的研究：使用3D模型了解地质过程

The studies show that 3D laser scanning is a useful measuring technique for highlighting changes to natural structures. The data obtained can be used to help interpret other geological information, Santagata says, “For example, the variations highlighted by comparing the Lechuza cave studies provided interesting data that can easily be correlated to the rainfall that occurred in this area between the two survey campaigns.”

“在cenote深渊的情况下，考虑到该区域在洞穴中的温度和气压传感器记录的表面和洞穴温度之间发生振荡，可能是由于温度变化而崩溃的。正在进行对洞穴该区域的详细环境监测，重复的3D模型将使我们能够理解这些过程对于阿尔卑斯山中的冰洞​​的起源和开发是否重要。”

Explore the projects in 3D:
Atacama Salt Caves
Atacama 3D Models
Cenote 2018 Expedition
Cenote 3D Models

Key people involved in the surveys: Tommaso Santagata (Vigea - Virtual Geographic Agency andLa Venta Esplorazioni Geografiche), Umberto Del Vecchio (Vigea - Virtual Geographic Agency andLa Venta Esplorazioni Geografiche), Jo De Waele (University of Bologna and La Venta), Francesco Sauro (University of Bologna and La Venta), Stefano Fabbri (University of Bologna/La Venta).

Lechuza洞穴探险是由La Venta Esplorazioni Geografiche协会组织的，并在博洛尼亚大学的怪异系的科学支持下，并于2015年与委员会的Grotte E. Boegan合作。地理社会，并在康纳夫智利的支持下实现。Cenote Monitoring是一个多学科项目，与La Venta，Benea的合作以及Fanes Sennes和Braies的区域公园与Studio GST和Eli Friulia的合作组织，该项目是冰川内部项目的一部分。Gruppo Grotte Treviso和Gruppo Speleologico Padovano。