**4. Results**

#### **4.1 Terminus fluctuations**

The history of the advances and retreats of Lys Glacier is summarized in **Figure 3**. We here report the complete record of data but also focus on the most recent period (1975–2017; see box in **Figure 3**). The general trend is one of retreat, after two short advance pulses during the Little Ice Age (LIA), culminating in 1822, when the glacier reached its peak LIA extension, and 1861. A very negative phase occurred between 1860 and 1882, when the glacier retreated by 941 m. This phase was followed by a short advance pulse at the end of the nineteenth century. The twentieth century saw an initial stability, with a small advance between 1913 and 1922, after which the glacier underwent an almost uninterrupted retreat, with the only exception of the short advance phase 1973–1985. The cumulative retreat since 1812 was 1.55 km, while since 1913 the glacier retreated by 847 m, with an average of −7.99 my<sup>−</sup>1.

From 1975 to 2017, Lys Glacier retreated for 32 out of the 43 years analyzed, with an average variation of −8.26 my<sup>−</sup><sup>1</sup> . Since the last short-lived advance phase ending in 1985, retreat totalled 443 m (−13.85 my<sup>−</sup><sup>1</sup> ). Retreat rates were particularly high between 2003 and 2007, with the most negative variations of −45 m (2007) and − 38 m (2003), while 1991 saw a very short readvance (+8 m), and in 2002 the glacier was considered stable. Retreat rates became lower after 2007, at −7.55 my<sup>−</sup><sup>1</sup> preluding to the separation of the glacier tongue from the parent glacier.

#### **4.2 Area and volume changes**

Over the period of observation, Lys Glacier underwent large changes in area. From 1975 to 1999, little change is evident on the western section of the glacier tongue (**Figure 4**), which reached the lowest elevations (ca. 2350 m a.s.l.). However, the easternmost part of the glacier tongue had already started retreating by 1999. Far greater changes than in the earlier period occurred from 1999 to 2014, with marked regression both in the western and eastern sections of the glacier tongue (**Figure 4a**). On the western section, the glacier tongue detached from the upper portion of the glacier at the base of an icefall, whereas on the eastern section the retreat exposed steep rocks underneath the ice. In 2014, the two main branches of the glacier still maintained a small connection at the base of a large rock outcrop (**Figure 4a**) and in the accumulation basins. Over the years, changes in Lys Glacier area were almost linear in rate, except for the first year, 1975, when the glacier had its largest area (11.3 km<sup>2</sup> ) of the period of observation (**Figure 5**). Since 1988, the area decreased at a rate of −0.045 km2 y<sup>−</sup><sup>1</sup> . In view of the high spatial resolution of the imagery, the uncertainty in the glacier outlines is below 2%, which supports the evidence of the general trend.

**175**

small size.

**Figure 3.**

*annual variations as well.*

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

Beside changes in the glacier area, recent years have also seen a transformation of the geomorphological setting of the glacier outwash plain. While the exact date marking the origin of glacier lakes is difficult to establish, by 1999 five small ice-contact lakes had formed on the glacier tongue. Progressive stagnation in the ablation area allowed the lakes to grow and new ones to develop. Thus, from five

*Lys glacier terminus fluctuations. The box indicates the observation period analyzed in further detail, showing* 

further lakes formed while the existing ones grew in size (**Figure 4b, c**). The area of glacier lakes increased almost exponentially (summing the area of all lakes) from

larger than that of the glacier outlines, up to 30% in 1999 because of their relatively

) a larger overall area is seen together

in 2014 (**Figure 5**). The uncertainty in the lake outlines is

in total). In 2014, three

scattered ponds in 1999 (totalling 1527 m2

1999, reaching 58,560 m2

with the coalescence in two larger lakes in 2006 (8730 m2

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

*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*

#### **Figure 3.**

*Glaciers and the Polar Environment*

**4. Results**

**4.1 Terminus fluctuations**

with an average variation of −8.26 my<sup>−</sup><sup>1</sup>

**4.2 Area and volume changes**

its largest area (11.3 km<sup>2</sup>

evidence of the general trend.

area decreased at a rate of −0.045 km2

ending in 1985, retreat totalled 443 m (−13.85 my<sup>−</sup><sup>1</sup>

weather station measures air temperature, total precipitation (by a heated gauge) and snow height (by an automatic webcam) every hour. The contemporary presence of manual and automatic instruments has allowed ensuring the homogeneity and continuity of the series. Although a weather station also exists at a higher elevation and closer proximity to Lys Glacier (Alpe Courtlys, 1992 m a.s.l., 2.5 km distance), this station was installed in 2001 and does not permit a long-term analysis of climate variables. In this study, we calculated monthly, seasonal and annual averages of air temperatures and monthly, seasonal and annual cumulated liquid/

The history of the advances and retreats of Lys Glacier is summarized in **Figure 3**. We here report the complete record of data but also focus on the most recent period (1975–2017; see box in **Figure 3**). The general trend is one of retreat, after two short advance pulses during the Little Ice Age (LIA), culminating in 1822, when the glacier reached its peak LIA extension, and 1861. A very negative phase occurred between 1860 and 1882, when the glacier retreated by 941 m. This phase was followed by a short advance pulse at the end of the nineteenth century. The twentieth century saw an initial stability, with a small advance between 1913 and 1922, after which the glacier underwent an almost uninterrupted retreat, with the only exception of the short advance phase 1973–1985. The cumulative retreat since 1812 was 1.55 km, while

solid precipitation for the analysis of climatological conditions.

since 1913 the glacier retreated by 847 m, with an average of −7.99 my<sup>−</sup>1.

preluding to the separation of the glacier tongue from the parent glacier.

From 1975 to 2017, Lys Glacier retreated for 32 out of the 43 years analyzed,

high between 2003 and 2007, with the most negative variations of −45 m (2007) and − 38 m (2003), while 1991 saw a very short readvance (+8 m), and in 2002 the glacier was considered stable. Retreat rates became lower after 2007, at −7.55 my<sup>−</sup><sup>1</sup>

Over the period of observation, Lys Glacier underwent large changes in area. From 1975 to 1999, little change is evident on the western section of the glacier tongue (**Figure 4**), which reached the lowest elevations (ca. 2350 m a.s.l.).

However, the easternmost part of the glacier tongue had already started retreating by 1999. Far greater changes than in the earlier period occurred from 1999 to 2014, with marked regression both in the western and eastern sections of the glacier tongue (**Figure 4a**). On the western section, the glacier tongue detached from the upper portion of the glacier at the base of an icefall, whereas on the eastern section the retreat exposed steep rocks underneath the ice. In 2014, the two main branches of the glacier still maintained a small connection at the base of a large rock outcrop (**Figure 4a**) and in the accumulation basins. Over the years, changes in Lys Glacier area were almost linear in rate, except for the first year, 1975, when the glacier had

y<sup>−</sup><sup>1</sup>

the imagery, the uncertainty in the glacier outlines is below 2%, which supports the

) of the period of observation (**Figure 5**). Since 1988, the

. In view of the high spatial resolution of

. Since the last short-lived advance phase

). Retreat rates were particularly

**174**

*Lys glacier terminus fluctuations. The box indicates the observation period analyzed in further detail, showing annual variations as well.*

Beside changes in the glacier area, recent years have also seen a transformation of the geomorphological setting of the glacier outwash plain. While the exact date marking the origin of glacier lakes is difficult to establish, by 1999 five small ice-contact lakes had formed on the glacier tongue. Progressive stagnation in the ablation area allowed the lakes to grow and new ones to develop. Thus, from five scattered ponds in 1999 (totalling 1527 m2 ) a larger overall area is seen together with the coalescence in two larger lakes in 2006 (8730 m2 in total). In 2014, three further lakes formed while the existing ones grew in size (**Figure 4b, c**). The area of glacier lakes increased almost exponentially (summing the area of all lakes) from 1999, reaching 58,560 m2 in 2014 (**Figure 5**). The uncertainty in the lake outlines is larger than that of the glacier outlines, up to 30% in 1999 because of their relatively small size.

#### **Figure 4.**

*Area changes of Lys glacier and its proglacial lakes over sample years. (a) Lys glacier outlines in 1975, 1999 and 2014. Background is the orthorectified Pleiades satellite image from 2014. (b) the glacier terminus and two proglacial lakes in 2006. (c) the glacier terminus and proglacial lakes in 2014.*

#### **Figure 5.**

*Changes in the area of Lys glacier, its proglacial lake and supraglacial debris cover over the period of observation.*

The DEM comparison shows a very different picture in the glacier tongue compared to the other areas of the glacier. On the tongue, large negative changes occurred, particularly on the western section, with a maximum of 136.52 m ice loss.

**177**

**Figure 6.**

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

On the eastern part of the ablation tongue, the decrease in ice thickness reached instead 41 m. Aside from the glacier tongue, the other areas of the glacier show a more complex pattern, with areas of both positive and negative changes occurring. A loss in glacier thickness is seen particularly in the lower sectors of the western glacier tongue and in a narrow band in the uppermost reaches of the western accumulation basin, as well as on the eastern tongue in its lower easternmost area (**Figure 6**). A positive difference from 1991 to 2014 can instead be seen particularly on the western accumulation basin, where an apparent increase in thickness is

*Thickness changes of Lys glacier from 1991 to 2014. Negative values represent loss in ice thickness. The* 

*background image is the hillshade produced from the Pleiades DEM acquired in 2014.*

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

*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*

On the eastern part of the ablation tongue, the decrease in ice thickness reached instead 41 m. Aside from the glacier tongue, the other areas of the glacier show a more complex pattern, with areas of both positive and negative changes occurring. A loss in glacier thickness is seen particularly in the lower sectors of the western glacier tongue and in a narrow band in the uppermost reaches of the western accumulation basin, as well as on the eastern tongue in its lower easternmost area (**Figure 6**). A positive difference from 1991 to 2014 can instead be seen particularly on the western accumulation basin, where an apparent increase in thickness is

#### **Figure 6.**

*Thickness changes of Lys glacier from 1991 to 2014. Negative values represent loss in ice thickness. The background image is the hillshade produced from the Pleiades DEM acquired in 2014.*

*Glaciers and the Polar Environment*

**176**

**Figure 5.**

*observation.*

**Figure 4.**

The DEM comparison shows a very different picture in the glacier tongue compared to the other areas of the glacier. On the tongue, large negative changes occurred, particularly on the western section, with a maximum of 136.52 m ice loss.

*Changes in the area of Lys glacier, its proglacial lake and supraglacial debris cover over the period of* 

*Area changes of Lys glacier and its proglacial lakes over sample years. (a) Lys glacier outlines in 1975, 1999 and 2014. Background is the orthorectified Pleiades satellite image from 2014. (b) the glacier terminus and two* 

*proglacial lakes in 2006. (c) the glacier terminus and proglacial lakes in 2014.*

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 average of −4.34 m and a volume change of −47.06 × 106 m3 .
