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10/2016

Glacier Field Course in Switzerland 2016

Hydrological and meteorological observations

at the proglacial lake of Rhonegletscher

Roisu Yamasaki1,

Eva de Andrés Marruedo2,

Cayetana Recio Blitz2

1 Graduate school of environmental science, Hokkaido University.

2 Numerical Simulation in Science and Engineering (GSNCI) ETSI de Telecomunicación.

Universidad Politécnica de Madrid.

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1. Introduction

Rhonegletscher is a glacier of the Swiss Alps, in the canton of Obergoms VS (Figure

1). It has been very popular for visitors due to mainly two reasons. First, it is the water

source of one of Europe's largest river; the Rhone river. Second, it is easily accessible

from the Furka pass road, situated at about 2300 m a.s.l. From 1874 to 1915, one of the

most complete surveys was carried out in Rhonegletscher, and the first detailed

topographic map of a glacier was accomplished (Mercanton, 1916). The results of these

efforts, this glacier gains world-wide reputation in the glaciological community.

Figure 1: Map of Rhonegletscher location. (Omoto and Ohmura, 2015)

Recently, due to global warming, Rhonegletscher is retreated and made glacial lake

(proglacial lake) at the front of Rhonegletscher (Figure 2). Proglacial lake accelerates

ablation of glacier and it has a risk as the lake bursts by increasing water level, in case a

large ice block collapses into water (Tsutaki et al., 2011).

Figure 2: Rhonegletscher and proglacial lake (September, 2016).

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As shown in Figure 3, over the last 150 years, Rhonegletcsher has retreated from

Gletsch to Belvèdere, and some studies suggested 30% of mass lost (Huss et al., 2008a).

Figure 3: Plane figure showing the retreat of the Rhone Glacier between 1602 and 2014.

Red line indicates shoreline of Rhonesee observed in September, 2014. (Omoto and

Ohmura, 2015)

Currently, this glacier is located at an altitude between 2300 to 3500 m a.s.l., with the

highest part oriented northward and limited by Eckstock peak; the mountain reaches

3557 meter. Also, this glacier is enclosed in a valley formed by Gästenhörner at the

western side and Galestorn at the east. The glacier surface covers almost 16 km2, with a

total volume estimated in 2.063 km3 (2007) and the value is smaller recently. (Table 1)

Table 1: Surface area and ice volume of Rhonegletscher for different years for which a

digital elevation model of the glacier surface exists (Farinotti et al., submitted).

There is a proglacial lake placed at the terminus and it was produced by ice melting

water filling a basin in front of the glacier. From bed topography studies, this lake is

expected to grow, reaching a potential lake volume amounts of 10.2 × 106 m

3 of water,

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with an averaged depth of 22 m and a maximum of 71 m (Zanho, 2004).

What will lead to change the configuration and the recession of Rhonegletscher? For

example, we can think that its retreat may be somewhat related with the global warming

trend, since the higher atmospheric temperatures, the more melting would be expected.

Another circumstance which encourages ice melting would be the change of snowfall,

i.e., decrease snowfall causes less accumulation. But, have these questions already been

studied in Rhonegletscher? Some numerical models have been run under different

scenarios, trying to answer this kind of questions and trying to reveal the estimations of

Rhonegletscher retreat rates (Sugiyama et al., 2007) as well as the drift in the seasonal

runoff peak, which is supposed to vary from July-August to May-June (Huss et al.,

2008b). As we have seen, Rhonegletscher is a very well-studied and monitored glacier,

with a big dataset that allows us the opportunity to keep going further in order to

understand important and crucial aspects of alpine glacier behavior and trends.

Our fieldwork has been carried out for several days in September, every year since

2007. Therefore, our motivation becomes from the aspects that follows daily

fluctuations. Although many parameters have been surveyed on the glacier – such as

albedo, elevation of GPS-referenced points, and pH of surface melt waters, etc. –, we

focus on measurements of the proglacial lake and atmospheric environments, in order to

give a more comprehensive perspective. Apart from keeping increase the dataset, the

aims of this study relay on approximating lake-glacier dynamics in terms of: (1)

identifying daily variations in height of lake-level surface; (2) determining circulation

patterns by observing iceberg movement; (3) co-relating parameters in order to reveal

possible triggers.

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2. Method

We did three observations (metrological observation, logging of glacial lake

variability, photogrammetry).The setting point of each observation is shown in

Figure 4. All of the observations were logged from about 9/2 18; 00 to 9/4 10; 00.

The detail of each observation is following.

Figure 4: The setting point of each observation.

A) Metrological observation (Vaisala WXT510)

Vaisala Weather Transmitter WXT510 (Figure 5) is a multi-sensor instrument that

measures six weather parameters. This equipment consists of the sensors, and by

connecting it to a data logger, it allows us to obtain continuous measure of climatic

components listed below (Field manual for Swiss glacier course, 2006). We set this

equipment on the land at east side of the glacier.

Wind speed and direction (horizontal)

Wind speed and direction are measured using the array of three equally

spaced ultrasonic transducers (three small poles) on the top of the instrument.

Liquid precipitation

The precipitation is by the sensor under the metal plate that covers the top of

the instrument, detecting the impact of individual raindrops.

Barometric pressure and Temperature and relative humidity

Barometric pressure, temperature and humidity measurements are done by the

sensor module in the inner part of the instrument, behind the radiation shield.

Logging of

proglacial lake

Photogrammetry

Metrological observation

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B) Logging of lake variability.

We used HOBO U20 (Figure 6) water level and water temperature logger for

recoding water pressure, water temperature and air temperature. The measurement

was 5 min intervals. The logger for measuring water pressure and temperature was

fixed to a bar (Not to move in water) and it was set at lake shore (Figure 7, 8). The

logger for measure of air parameters was set on the land near the water logger

(Figure 8).

Figure 6: HOBO U20 water level and water temperature logger. One used for

recoding water pressure, another used for recoding air pressure.

Figure 7: Logger for water parameters was fixed to a bar.

Figure 5: WXT510 Cut away view (WXT510 users guide)

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Figure 8: Installation of the logger.

Since this loggers cannot measure directly the change of water level, we used

following the equation (hydrostatic pressure) to calculate the change in the water

level from water pressure and air pressure.

h=(Pw-Pa)/ρg

h; water level [m]

Pw; water pressure [kPa]

Pa; air pressure [kPa]

ρ; density of water (= 1000 [kg/m3] )

g; Acceleration of gravity ( = 9.8 [m/s2] )

C) Photogrammetry

We used two interval cameras (GARDENWATCHCAM V1.0) to observe the

movement of icebergs floating on the proglacial lake (Figure 9). This technique is

able to determine the geometric properties of the icebergs and spatial situations.

The cameras were set on the land at the east side of the lake (Figure 10). Both two

cameras photographed the lake and the terminus part of the glacier, but the angle

was different (Figure 11). Photographs were taken with 5 min intervals except for

evening when the camera stops working. After shooting, we made videos by

connecting the photographs and we analyzed the movement of icebergs through the

observation period.

Logger for water Logger for Air

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Figure 9: Internal camera fixed to land.

Figure 10: The location of cameras for photogrammetry and photo area of each the

cameras (X, Y; Figure 11). (modify Omoto and Ohmura, 2015)

Figure 11: The photo area. (X, Y is defined in Figure 10)

Cameras

Y

X

Y X

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3. Results

A) Metrological observation

Wind was blowing during the entire sampling period, with speed varying from 0.5

to 3 m/s (Figure 12). Northeast was main wind direction (Figure 13). Note that the

time in Figure 12 is given in Swiss local time (Time in following figures is same).

Figure 12: Wind speed record

(metrological observation, 1st to 4

th September 2016)

Figure 13: Dominant wind component

(metrological observation, 1st to 4

th September 2016)

Highest air temperatures were at 15:00 h–16:00 h, corresponding with the lowest

relative humidity (Figure 14). Air temperature ranged from 6 ºC in the early

morning (6:00 h) to 17 ºC and relative humidity from 37 to 83 %. Air temperature

and humidity have inversely correlated patterns.

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Figure 14: Humidity and Air temperature

(metrological observation, 1st to 4

th September 2016)

Atmospheric pressure was measured both at the metrological observation site and

at the lake-shore station. In Figure 15, we observed higher pressures at lake shore

(788.8 to 785.9 kPa) compared to those at the metrological observation site (781.8

to 778.5 kPa), which is due to the elevation difference between the sites. Both

places registered a decreasing trend in time.

Figure 15: Air pressure at metrological observation site and lakeshore station.

B) Logging of lake variability

Minimum atmospheric temperatures were of about 6 ºC between 6:00 h–9:00 h in

the morning and continuously increasing to reach 17 ºC at around 17:00 h in the

afternoon (Figure 16, green line). Water temperature also started to increase from

0.8 ºC at 9:00, reaching its maximum of almost 4 ºC at 14:00 h to 15:00 h in the

afternoon (Figure 16, red line).

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Both atmospheric and water pressure were observed by data loggers in the

lake-shore station. To calculate the water level height above the underwater logger,

atmospheric pressure was removed and hydrostatic equation applied as described in

the method section. In terms of pressure, the underwater logger recorded values

from 79 to 83 kPa, which are translated to 0 to 40 cm of water column above the

sensor, i.e. from surface to - 0.40 m depth. Maximum peaks take place around

18:00 h and minimum at 9:00 h (Figure 16, blue line).

We can see that all of these parameters follow a similar daily pattern, starting to

increase at about 9:00 h in the morning. An interesting point of this observation is

that the water temperature peaked earlier than air temperature and water level,

which will discuss later.

Figure 16: The change of air and water temperature and water level of the lake.

The water level is relative to the depth of the sensor.

C) Photogrammetry

We have collected images for three days, from September 2 to 4 2016. These

photographs showed the movement of icebergs and suggested that the movement

seems to be periodic. These behaviors are more precisely explained below (Figure

17-20).

Since the photogrammetry was started at 14:15 of September 2, small icebergs are

constantly moving but the move is small. These small icebergs are located at this

time in the remotest of the glacier tongue area which is the end of glacier (left in

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Figure 17). This movement continues until 16:40 h at the same day, when suddenly

the main iceberg (which is larger) pivots on its axis. The main iceberg pivots

without moving until 20:30 h.

Figure 17: The image at 20:30 h of Sep.2

At 20:30 h, the main iceberg stops pivoting. And just at that moment, the small

icebergs move slowly. These icebergs move up to an intermediate area of the lake

while passing near the shore.

At night, the camera was not scheduled to collect images, so the first image of the

next morning (at 05:15 h of September 3, Figure 18) found small icebergs still at

the same place (in the intermediate zone lake) and they barely move around the

place. But between 05:15 h and 10: 45h, small icebergs began to move closer to the

glacier tongue (Figure 19).

Figure 18: The image at 5:15 h of Sep.3

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Figure 19: The image at 12:00 h of Sep.3

After this movement, small icebergs moved to the inner area of the lake while

drawing a curve, between 11:41 h and 14: 10 h (Figure 20). And they returned to

initial position (the other side of the glacier tongue; left in Figure 20).

Figure 20: The direction of the small icebergs movement

Small icebergs continue to move until 16: 40 h when the main iceberg pivots again.

Icebergs behavior is repeated over the three days. They moved approximately at the

same times and moved along the same path in the lake.

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4. Discussion

I. Metrological observation and logging of lake variability

Wind is controlled by the orientation of the glacier valley, which channelizes the

air masses, resulting in main wind direction of about 60°N (Figure 13). Because the

metrological observation was carried out near the glacier, it probably was

influenced by land air mass and glacier air mass depending on wind direction. Air

temperature and humidity showed anti-correlated sinusoidal curves (Figure 14).

This is because warmer air becomes more unsaturated.

Atmospheric pressure at both stations agrees with the elevation difference, being

higher at lower altitudes (Figure 15). The decreasing tendency in both curves

indicates that a low-pressure system was approaching, and this also accords with

the observation of clouds during the last day.

Next, we discuss Figure 16. The air temperature peak at the meteorological

observation takes place earlier than at the lake-shore station. This may suggest that

lake-shore station is affected higher influence of glacier and/or evaporation effect of

water. At 9:00 h in the morning, the lake-shore station begins to be exposed to

sunlight. It is observed that both upward trend curves of water temperature and

water level start going up at almost the same time but it is after air temperature

curve does. This means air is warmed earlier than water, and this agrees with

physics laws in terms of heat capacity. Therefore, water level is supposed to rise

because more insolation is received on glacier surface, which means air temperature

increase, advancing the surface melting, then runoff into the lake increases.

Another discussion in Figure 16 is the phenomenon which water temperature stops

increasing and starts decreasing about three hours before air temperature or water

level do (Figure 16a). Similar observation result was reported in preceding study

(Figure 21). This phenomenon is not consistent with what is expected from heat

capacity. Because the heat capacity of water is larger than that of air, water

temperature increase and decrease more slowly than the change of air temperature,

but these observations show inverted phenomenon.

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Figure 16a: Water (red) and air temperature (green), and water level (blue). The

red and yellow circles indicate the peaks in the water and air temperature,

respectively.

Figure 21: The change of water temperature and air temperature at same region in

September 2015 (Ishii and others, 2015). Blue and red line shows water and air

temperature respectively. The red circle point is faster than yellow circle as well as

Figure 16a.

Here, we discuss a hypothesis that may support such this inconsistent behavior.

Since the logger is located at surface level, it is plausible that water surface may be

warmed by solar radiation, since its albedo is relatively low (5-8%). However,

water reaches its maximum density at 4 ºC, and taking into account that meltwater

from the glacier is at the freezing/melting point of 0 ºC, it is feasible to think that

water from glacier melting will tend to reach the upper layers of the lake and the 4

ºC-warmed water laying in the surface will move downwards to occupy the bottom

layers. Indeed, Ishii and others, (2015) reported the lake had thermocline at 6m

depth. As a result, the surface water temperature of lake dramatically changed.

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II. Movement of icebergs

Throughout the days, as photogrammetry shows constantly icebergs moving, there

is subglacial discharge (entering new melting water) from the surface and/or bed of

Rhonegletcher into the lake. From field data, we see the highest water level of the

lake is at 18:00 h and the level rise is periodic (Figure 22). We consider this

periodic change of water level corresponds to the discharge behavior from the

glacier, which means a maximum discharge flow at 18:00 h.

Figure 22: The change of water level in the lake.

Note that the main iceberg pivots between 16: 00 h and 20:00 h. On the other hand,

small icebergs move in the whole day, which suggests there are continues

subglacial discharge. The relationship between the time of main iceberg pivoting

and the time of highest water level imply that the main iceberg movement is

controlled by the discharge behavior which is suggested by the change in water

level. Therefore, the magnitude of this discharge is not enough for moving the main

iceberg, but only several hours, it can influence the iceberg and occurs the pivoting.

Furthermore, we compare the movement route of icebergs in this research area

with earlier study and it shows a similar pattern (Figure 23).

Figure 23: A schematic diagram for horizontal movement of water in lake (modify

Ishii and others, 2015). The number shows the order of water movement.

Glacier

Iceberg

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Iceberg movements are very similar from year to year. Figure 23 shows that the

main water flow (number (1) in Figure 21; the same below) is pushed by glacier

tongue and it probably corresponds to the point of maximum subglacial discharge

flowing into lake. This main flow moves small icebergs quickly and pushes them

against the opposite side of the glacier tongue, then hits the wall of the lake. The

wall backs up the main flow (number (4)) and the flow returns along the shores of

the lake by inertia of water (number (5), (6)). The icebergs also return along with

the flow of water. Contrastively, only for a certain time, the main iceberg is

influenced by the main flow (it implies in number (2), (3)). This behavior is cyclic;

it is repeated again and again.

5. Conclusion and Future

We measured the change of water level with environmental parameter (ex. air

temperature, water temperature…). Our date shows that increasing air temperature

causes more ice melting and it leads higher water level in the proglacial lake. Also,

the icebergs movement in the lake permits us to understand how ice melted water

circulates in the lake and to suggest the relationship between the change of

environmental parameter and the change of discharge behavior.

We consider this daily variations study is so important to better understand the

Rhonegletscher behavior and need to continue this observation every year. As the a

reason for that, monitoring the daily variations of air and water temperature, height

water level and iceberg movements could help us to understand and estimate

potential trends in Rhonegletscher dynamics.

6. References

Farinotti, D., Huss, M., Bauder, A., Funk, M., and Truffer, M. (2009). A method to estimate ice

volume and ice thickness distribution of alpine glaciers. Journal of Glaciology. (submitted).

Huss, M., Bauder, A., Funk, M., and Hock, R. (2008a). Determination of the seasonal mass balance

offour Alpine glaciers since 1865. Journal of Geophysical Research, 113(F1):F01015.

Huss, M., Farinotti, D., Bauder, A., and Funk, M. (2008b). Modelling runoff from highly glacierized

alpine catchment basins in a changing climate. Hydrological Processes. doi:10.1002/hyp.7055.

Mercanton, P. L. (1916). Vermessungen am Rhonegletscher, Mensurations au Glacier du Rhône,

1874–1915. Neue Denkschriften der Schweizerischen Naturforschenden Gesellschaft, 52.

Sugiyama, S., Bauder, A., Funk, M., and Zahno, C. (2007). Evolution of Rhonegletscher,

Switzerland, over the past 125 years and in the future: application of an improved flowline model.

Annals of Glaciology, 46:268–274.

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Tsutaki, S., Nishimura, D., Yoshizawa, T., & Sugiyama, S. (2011). Changes in glacier dynamics

under the influence of proglacial lake formation in Rhonegletscher, Switzerland. Annals of

Glaciology, 52(58), 31-36.

Zahno, C. (2004). Rhonegletscher in Raum und Zeit: Neue geometrische und klimatische Einsichten.

Diplomarbeit an der VAW/ETH-Zürich, (unveröffentlicht).

小元久仁夫, 大村纂. (2015). 急速に後退するスイスのローヌ氷河. 地学雑誌,124(1), 127-135.

石井, 柑谷, 島田. (2015). ローヌ氷河の全縁湖における氷塊の挙動と水位変動. 2015年スイ

ス実習レポート.