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 agencyVigea最近使用了Leica Geosystems激光扫描解决方案在两个洞穴调查中：对智利Lechuza盐洞的形态（形式和结构）变化的研究，意大利的自然井冰洞。

Santagata explains how detailed scanning at intervals can offer insight into physical changes in cave environments, “Although most processes occurring in caves are relatively slow, some can be fast, such as erosion caused by flooding. These geological changes can be monitored by terrestrial laser scanning surveys and measured by comparing ‘before and after’ 3D models. It’s an interesting tool for making comparisons over time and is therefore increasingly being used in the study of climate change.”

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

Close 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 P40to perform 68 scans, including about 200-metres surveyed 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

第二项研究地下冰depo担忧sit in the Cenote Abyss, one of the deepest and most voluminous caves of the Italian Dolomites. The 280metre-deep ice cave was discovered in 1994 after the entrance opened as a result of the abrupt emptying of a small lake in the Regional Park of Fanes, Sennes and Braies. The cave’s vertical entrance consists of a massive 130metre-thick layered ice deposit; at the lower limit of the ice-filled entrance part a shaft opens – ice-free and 165 metres deep – leading into a dome-shaped chamber occupied by a cave rock glacier.

激光扫描调查于2015年，2016年进行，并于2018年允许Santagata的团队估计由于崩溃并获取数据以进行完整监测项目而导致的变化。2015年10月的首次探险包括使用基于HDS7000阶段的激光扫描仪对最终腔室进行完整的3D激光扫描调查。这项调查提供了腔室（420,000立方米）的详细体积，以及从天花板上悬挂的冰块和底部岩石冰川的冰块位置的第一个记录。在这次探险中以及随后在2016年和2018年的探险中，洞穴的其他部分使用扫描仪P40进行了3D扫描。

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.”

使用两种不同的方法比较点云：首先，我们进行了两个数据集之间的快速比较，以了解将我们更详细的分析集中在哪里。其次，我们提取了感兴趣领域的几个“切片”。我们向这些区域出口以进行完全数字化，以更好地估计岩石倒塌的量，约为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。”

探索3D中的项目：
Atacama Salt Caves
Atacama 3D型号
Cenote 2018探险
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).

The Lechuza cave expeditions were organised by the Association La Venta Esplorazioni Geografiche with the scientific support of the BIGEA Department of the University of Bologna and with the collaboration of the Commissione Grotte E. Boegan in 2015. The scientific expedition in 2018 received funding from the National Geographic Society and was realised with the support of CONAF Chile. The Cenote monitoring is a multidisciplinary project organised as part of the Inside the Glaciers project with the collaboration of La Venta, BIGEA and the Regional Park of Fanes Sennes and Braies with the collaboration of Studio GST and Eli Friulia, the Speleo Club Proteo of Vicenza, the Gruppo Grotte Treviso and the Gruppo Speleologico Padovano.