*3.1.1 Point cloud analysis*

DEMs obtained during LiDAR and TLS surveys and from photographic SfM acquired by drones and helicopter-borne cameras allow monitoring the morphology evolution of the glacier surface. In addition, the DEM of difference (DoD) calculation permits to estimate the surface elevation changes and the possible ice mass loss. From the DoD obtained with the DEMs acquired in October 2019 and June 2014 (helicopter-borne SfM and LiDAR respectively), one can observe the glacier thinning of more than 10 m on average (**Figure 3**). In the considered period, the terminus retreated by several tenths of metres and the bedrock remained exposed. In this part, the DoD shows a thickness loss of 30–40 m approximately, which corresponds to the glacier thickness in 2014.

#### **Figure 3.**

*DEM of difference (DoD) of the Montitaz Lobe. The DoD is calculated as the difference between the DEMs acquired on 1/10/2019 and 9/6/2014. The glacier outlines in both years are represented as dashed lines.*

**131**

**Figure 4.**

*was predicted 10 days in advance.*

*Close-Range Sensing of Alpine Glaciers DOI: http://dx.doi.org/10.5772/intechopen.92841*

*3.1.3 Time-lapse camera applications*

usually lower than 1000 m3

RTS measurements are continuously active since 2010 to monitor the surface velocity of the Whymper Serac. The survey is conducted with a Leica TM30 that operates in ATR mode. The prism network is composed of several stakes installed into the unstable portions, while a few prisms placed in the surrounding bedrock serve as reference points. Complete acquisition of the entire network lasts approximately 45 min and it is conducted every 2h. The sensor-to-target distance is of 4800 m on average, which is beyond the instrument operating limits declared by the manufacture in ATR mode (https://w3.leica-geosystems.com/downloads123/zz/ tps/tm30/brochures-datasheet/tm30\_technical\_data\_en.pdf). In addition, extreme atmospheric conditions linked to the high-mountain elevation occur frequently. This situation makes the Whymper Serac a critical scenario for RTS measurements and a robust processing method has been developed ad hoc [11]. However, the RTS data allowed forecasting 10 days in advance the serac break-off of 22/10/2014 [12].

The surface kinematics of the Planpincieux Glacier right lobe has been deeply

. Slab fracture instability is caused by the aperture of

. Water

investigated with image analysis of 6-year-long time-lapse monitoring. The data analysis allowed characterising the terminus dynamics and classifying the instability processes that cause break-offs: (i) disaggregation, (ii) slab fracture and (iii) water tunnelling [7]. Disaggregation is the progressive toppling of small ice pieces caused by the movement of the terminus beyond the frontal bedrock cliff. It is the most frequent process and it involves break-offs of limited size,

a crevasse orthogonal to the motion direction, located in correspondence to the maximum tensile stress line. When the fracture reaches the bedrock, it triggers a

tunnelling refers to the formation of R-channels [52] where a large amount of

*RTS measurements of prisms 13, 14, and 2b before the failure of 22/09/2014. Using these data, the break-off* 

large break-off of an ice lamella that can assume a volume of 104–105 m3

The RTS data acquired before such an event are shown in **Figure 4**.

*3.1.2 RTS applications*
