**4.3 Debris cover evolution**

On Lys Glacier, debris initially increased from 1988 to 2000, when it reached almost 1.3 km2 on the glacier tongue (**Figures 5** and **7a**). In 1988, debris was present in narrow medial moraines and more abundantly at the terminus (**Figure 2**). In 2000, a more homogeneous coverage of the glacier tongue can be seen (**Figure 7b**), as a mantle of debris appears covering the glacier at the higher elevations at the margins of the western tongue, also suggesting a possible input from the lateral valley walls; conversely, on the eastern tongue and parts of the eastern accumulation basin, coverage is sparse and patchy. Since 2000, the expansion of supraglacial debris appears to have halted as the total area decreased (**Figure 5**): this effect was probably caused by the shrinking of the stagnating glacier tongue, which was however entirely debris-covered by 2005 (**Figure 7c** and **d**). The spread of supraglacial debris appears to have slowed down also at the higher elevations, although limited evidence for increasing coverage is seen for the eastern tongue of the glacier. The relatively high slope and the consequent presence of seracs might limit debris accumulation in those areas.

The accuracy of debris cover maps was evaluated separately for 2006 and 2012, as seen in **Tables 2** and **3**. In both years, PA and UA are very high for debris: both are 100% in 2006, while PA is 89% and UA 97% for 2012. Overall accuracy was 83% in 2006 and 71% in 2012. The limited overall accuracy in both tests is mostly caused by the difficulty in distinguishing between snow and ice (**Figure 7b**, where no ice was identified), which however is not crucial for the analysis of debris cover. We estimate the accuracy of debris cover mapping in other years to lie between the two values reported for 2006 and 2012; however, it is also possible that the debris cover

**179**

*Variations of Lys Glacier (Monte Rosa Massif, Italy) from the Little Ice Age to the Present…*

*Accuracy estimation for debris cover classification based on the aerial orthophoto from 2006.*

*Accuracy estimation for debris cover classification based on the aerial orthophoto from 2012.*

Predicted Debris 13 0 0 0 13

**Manually classified**

Ice 0 21 17 0 38 Snow 0 0 48 0 48 Shadow 0 0 0 1 1 Totals 13 21 65 1 100

**Manually classified**

Ice 5 8 23 0 36 Snow 0 0 20 0 20 Shadow 0 0 0 0 0 Totals 48 8 43 1 100

**Debris Ice Snow Shadow Totals**

**Debris Ice Snow Shadow Totals**

amount after 2000 was underestimated, owing to the larger presence of snow cover and shadows in areas which were otherwise classified as debris-covered in previous

Predicted Debris 43 0 0 1 44

Due to its high altitude and position, Lys valley experiences cold winters and temperate summers. Heavy rainfall can occur when south humid Mediterranean winds blow and collide against the orographic barrier of the southern slopes of Monte Rosa. Perturbations from the west and northwest are more frequent, but they discharge their rain/snow content mainly on the Mont Blanc and Valais areas,

From 1928 to 2018 (excluding the period 1962–1970 when the station was temporarily moved downvalley), the mean annual temperature at Gressoney d'Ejola station was +4.4°C ranging from +2.6°C in 1984 to +6.1°C in 2015. Since we cannot focus on the commonly used 30-year reference period (1961–1990), we considered 1952–1961 and 1971–1990. Over this period of observation, the mean annual temperature was +4.0°C, slightly lower than the average of the past 30 years (1989–2018), which was +4.6°C. Climate warming is more evident when summer temperatures are compared: from +11.6°C during 1952–1961/1971–1990 to +12.7°C during 1989–2018, with a mean of +12.2°C over the whole period. The hottest month is July with a mean temperature of +13.2°C followed by August (+12.7°C) and June (+10.7°C). Generally, every 3 years the maximum daily of +25°C is recorded, even if the absolute maximum (+28.2°C) was observed on 4 August 2017 and 11 August 2003; 2003 was the hottest summer on record (average + 15.4°C; **Figure 8**) with relatively low amounts of liquid precipitation (216.6 mm corresponding to 74% of the mean summer total, 293.6 mm). Conversely, the coldest summer was 1977 (+9.9°C) with very heavy

leaving the northeastern extremity of the Aosta Valley almost dry.

rainfall (428.6 mm corresponding to 146% of the mean summer total).

*DOI: http://dx.doi.org/10.5772/intechopen.91202*

years (compare **Figure 7b, c** and **d**).

**4.4 Climatological analysis**

**Table 2.**

**Table 3.**

**Figure 7.** *Evolution of debris cover for Lys glacier. (a) 1988; (b) 2000; (c) 2005; (d) 2014.*

*Variations of Lys Glacier (Monte Rosa Massif, Italy) from the Little Ice Age to the Present… DOI: http://dx.doi.org/10.5772/intechopen.91202*


**Table 2.**

*Glaciers and the Polar Environment*

**4.3 Debris cover evolution**

accumulation in those areas.

almost 1.3 km2

age of −4.34 m and a volume change of −47.06 × 106

observed between 10 and 20 m, and a maximum of above +75 m was recorded. Considering the entire glacier, the ice loss signal is still predominant, with an aver-

On Lys Glacier, debris initially increased from 1988 to 2000, when it reached

The accuracy of debris cover maps was evaluated separately for 2006 and 2012, as seen in **Tables 2** and **3**. In both years, PA and UA are very high for debris: both are 100% in 2006, while PA is 89% and UA 97% for 2012. Overall accuracy was 83% in 2006 and 71% in 2012. The limited overall accuracy in both tests is mostly caused by the difficulty in distinguishing between snow and ice (**Figure 7b**, where no ice was identified), which however is not crucial for the analysis of debris cover. We estimate the accuracy of debris cover mapping in other years to lie between the two values reported for 2006 and 2012; however, it is also possible that the debris cover

in narrow medial moraines and more abundantly at the terminus (**Figure 2**). In 2000, a more homogeneous coverage of the glacier tongue can be seen (**Figure 7b**), as a mantle of debris appears covering the glacier at the higher elevations at the margins of the western tongue, also suggesting a possible input from the lateral valley walls; conversely, on the eastern tongue and parts of the eastern accumulation basin, coverage is sparse and patchy. Since 2000, the expansion of supraglacial debris appears to have halted as the total area decreased (**Figure 5**): this effect was probably caused by the shrinking of the stagnating glacier tongue, which was however entirely debris-covered by 2005 (**Figure 7c** and **d**). The spread of supraglacial debris appears to have slowed down also at the higher elevations, although limited evidence for increasing coverage is seen for the eastern tongue of the glacier. The relatively high slope and the consequent presence of seracs might limit debris

 m3 .

on the glacier tongue (**Figures 5** and **7a**). In 1988, debris was present

**178**

**Figure 7.**

*Evolution of debris cover for Lys glacier. (a) 1988; (b) 2000; (c) 2005; (d) 2014.*

*Accuracy estimation for debris cover classification based on the aerial orthophoto from 2006.*


**Table 3.**

*Accuracy estimation for debris cover classification based on the aerial orthophoto from 2012.*

amount after 2000 was underestimated, owing to the larger presence of snow cover and shadows in areas which were otherwise classified as debris-covered in previous years (compare **Figure 7b, c** and **d**).
