## 3 Results and Discussion
### The 2018 \"Plowing\" Event  
In its press release of 29 January 2018 [9], the Ministry of Culture in Peru reported that despite the presence of warning signage indicating the heritage site and prohibiting access to the protected area, in the late afternoon of 27 January 2018, a truck diverted off the paving of the Pan-American Highway at kilometre 424 and entered the protected area. A series of aerial photographs was collected by the Ministry on 28 January 2018 at 8.30 am by using a camera onboard a drone [9], and revealed that the incident visibly disturbed the area [22; 23]. In particular, the truck crossed over three linear geoglyphs, and left deep tire marks across an area of 50 by 100 m [9]. The photographs available online suggest that the truck was travelling towards the southeast (i.e., the direction of Nasca), and drove off the road around 100 m before a guardhouse installation point along the Pan-American Highway (see also Figure 2a for reference). The tire marks run for 100 m from the entrance point off the highway and towards the guardhouse and then turn right towards the west. Videos published on the web (e.g., [24]) show that the truck was parked 20-30 m away from the guardhouse before sunset on 27 January 2018. From this position, the truck likely was then driven back onto the highway towards the northwest (i.e., the direction of Palpa) after the incident. Based on published web evidence and the analysis of the VHR optical image in Google Earth, the location of the event can be placed at approximately 14 deg41'22\"S, 75 deg07 deg05\"W, just off the southwestern side of the Pan-American Highway (see black star in Figure 1). Figure 4a schematically represents: (i) a sketch of the tire marks left by the truck, as inferred based on photographic evidence [22; 23]; (ii) the position of the truck on 27 January 2018, as inferred based on the video [24]; and (iii) the location of the guardhouse, as determined via the VHR Google Earth image (see also Figure 2a). It is understood that this is not meant to be a forensic reconstruction of the event, but rather an attempt to spatially map objects and marks to better interpret the patterns found in the InSAR coherence maps. The surface disturbance that was caused by the \"plowing\" and was captured in the photographs consists in the alteration of the fragile surface of the Pampa de Jumana via removal of the reddish pebble and the uncovering of the much lighter grey-yellow clay underneath. Figure 3 provides a zoom onto the section of the Pan-American Highway that runs across the Pampa in its transect richest in geoglyphs and lines, including the area where the 2018 event occurred and also where the 13-m tall observation tower (_Torre Mirador de Las Lines de Nasca_) is located. Up from the latter, tourists can get a panoramic outlook of the Pampa and a close-up view of some of the geoglyphs, such as the \"Hands\" (_Las Manos_) and \"Tree\" (_Arbol_), as indicated in Figure 2b. Overall, the analysis of InSAR coherence maps for one pre-event (18/01/2018-26/01/2018; Figure 3b) and three cross-event (26/01/2018-30/01/2018, 10/01/2018-30/01/2018, and 13/12/2017-30/01/2018; Figure 3c-e) pairs reveals that generally most of the area shows high to very high coherence values (\(\gamma\) of 0.7 to over 0.9) across the Pampa. This indicates good correlation between the COSMO-SkyMed images composing each InSAR pair and the absence of significant elements of decorrelation. Apparent coherence loss and drop to values lower than 0.4 are observed for the following areas, due to a combination of imaging-related causes and human activity:  
* Pampa de Jumana: coherence across the plain decreases with increasing normal baselines due to geometric decorrelation. Pairs 26/01/2018-30/01/2018 (\(B_{p}\) of 472 m) and 10/01/2018-30/01/2018 (\(B_{p}\) of 165 m) in Figure 3c,d highlight a much more pronounced effect of geometric decorrelation than pairs 18/01/2018-26/01/2018 (\(B_{p}\) of 4 m) and 13/12/2017-30/01/2018 (\(B_{p}\) of 19 m) in Figure 3b,e.