Friday, February 16, 2018

January snowcover



The 2017 'short rains' season brought very little snow accumulation to the summit this year. Although snowfall is often variable during the short rains (typically November and December), this year was especially dry and resulted in a net lowering of glacier surfaces.

Early January brought the first noteworthy snow accumulation to the glaciers since the dry season began in June 2017. The graph above,
illustrating January snowfall, is based on snow measurements obtained from the Northern Icefield AWS by satellite telemetry. Such measurements must always be viewed cautiously, as wind redistribution of snow and other factors can complicate data interpretation - yet as average measurements from 2 sensors, their reliability is improved.

Snowfall is critically important to Kilimanjaro glaciers, primarily by controlling the amount of solar radiation reflected from the surface. When a bright snowcover exists, the reflectivity (albedo) is high; aging snow becomes gradually less reflective, and thinning snow allows radiation to penetrate through to the underlying glacier ice.

On the graph above, numbered squares correspond to a selection of natural-color images from the ESA (European Space Agency) Sentinel-2 satellite, shown below. These depict snow accumulation steadily increasing during early January, culminating in the events of 10 and 11 January. With little precipitation through the balance of the month and into early February, the mountain's snowcover then thinned and became patchier.

Here are a few notes on the Sentinel-2 images, which qualitatively demonstrate that
Kilimanjaro glaciers are sensitive to the magnitude, frequency, and spatial extent of precipitation events!

Image #1, 30 December 2017:  Clouds to the west of Kibo, filling the Western Breach and obscuring the southern slope glaciers. Within the caldera and south of the crater rim, uniformly-white areas are glaciers (likely with some snowcover). No snowcover is present within the caldera, with only a light dusting on the highest northern slopes, and some accumulation on the north-facing section of the caldera rim (e.g., below Uhuru Peak).
 
Image #2, 9 January 2018:  Extensive clouds, yet uniform snowcover is visible within the caldera. Note the lack of snow on a small portion of Reusch Crater (dark area), where geothermal heat flux is probably responsible for melting any accumulation. The graph above shows that this image represents snowcover prior to the two largest snowfall events of January, on the 10th and 11th.

Image #3, 14 January:  Little or thin cloud cover is present over the Kibo caldera, in contrast to the clouds obscuring the mountain's western and southern flanks. Snowcover is extensive, as suggested by the graph above.

Image #4, 24 January:  Scattered clouds surround the mountain at elevations below ~5,000 m. Snowcover from early January has thinned within the caldera and on the glacier (see graph), and generally become patchier. Albedo of the glacier surfaces remains high, reflecting most of the incoming solar radiation. The Reusch Crater is now mostly snow-free, and limited snow remains within the Western Breach. Climbers going to the summit on this date were likely walking on snow most of the distance above Stella Point.

Image #5, 8 February:  A typical February day on Kibo, with scattered clouds concentrated to the south and west. Snowcover patches within the caldera have shrunk further. Note the almost complete lack of snow on eastern and south-facing slopes; even at only 3° south latitude, solar radiation receipt is greater on south-facing than north-facing slopes in early February!

Tuesday, November 21, 2017

South-side glaciers


As late as the 1980s, three distinct bodies of ice remained on Kilimanjaro's caldera rim and spilled over onto the slopes. A century earlier, these icefields - the Northern, Eastern, and Southern - were more-or-less connected as one large ice cap. The map below (after Hastenrath, 1984) depicts the three icefields along with their outlet glaciers, which became more distinct as the ice thinned and retreated.

The mountain's south side is shown in the image above, from a rarely-seen perspective above the village of Mweka. The Diamond Glacier can be seen on the left-hand side; this thin feature appears more like a perennial snowpatch than a glacier, supported by the recent appearance of rocks protruding through the snow and/or ice. At the center of the image is the Kersten Glacier, which separated into upper and lower sections ~10 years ago. Two small blocks of ice left of the Kersten are all that remain of the Heim Glacier, which rivaled the Kersten in length 20-25 years ago. The fragmented ice on the right-hand side is what remains of the Decken Glacier. And in the upper-right corner is the Rebmann Glacier; this portion of the former Southern Icefield is visible from the trail between Stella Point and Uhuru Peak - as well as from Barafu Camp.

Glaciers on Kilimanjaro remain beautiful, and continue to reveal secrets of both their history and that of the mountain's climate. The "Roof of Africa" will be a very different place when the glaciers are gone.


Friday, October 20, 2017

At the summit: days #92-96 in the crater

This month we returned to Kilimanjaro's summit glaciers and automated weather stations, 14 months since our last visit (Aug. 2016). Yes, the changes were dramatic - everywhere we looked.

This post provides a few glimpses of the remaining ice, still incredibly beautiful. Once an initial inspection is done on recovered AWS data, a subsequent post will provide an overview.

Helping out on this fieldwork were Spencer and Chang'a (Fig. 1). This was both of their first times on the mountain and both brought new insights and questions, providing stimulating discussions during the ascent and in camps. Dr. Ladislaus Chang'a is Director of Research and Applied Meteorology at the Tanzania Meteorological Agency (TMA), and involved with the IPCC. He will be coordinating our new data- and information-sharing collaboration with TMA, hopefully as part of WMO's Global Cryosphere Watch.


As previous entries have mentioned, the past year has been drier than normal at the summit. Decreased albedo has resulted in considerable ablation of both vertical and horizontal surfaces. Indeed, ice loss at the surface caused an unprecedented number of ablation stakes to melt out, and the tipping of several instrument towers. With essential support from our Summit Expeditions (SENE) crew (photos here and here), the towers were reset after 4 nights camped at the summit (see Fig. 2 & 3) and everyone descended safely.

The Furtwängler Glacier provides one illustration of the speed with which glaciers are shrinking on the mountain (Fig. 6). Since February 2000, when Henry Brecher determined the glacier area from aerial photographs, more than 80 percent of this glacier has disappeared. A brief historical perspective on this glacier is available here. The linear rate of area decrease suggests that there will be nothing left of the Furtwängler by 2025.

Many thanks to longtime collaborator Thomas Mölg for helping to support this fieldwork!


Figure 1.  Spencer Hardy and Dr. Ladislaus Chang'a at Barafu Camp (4,670 m), our fifth night of the ascent.

Figure 2.  Looking west over the Northern Icefield. Visible instrumentation includes (left to right) a timelapse camera, high-accuracy temperature and radiation measurement (Climate Reference Network compatible), and the original AWS. Several ablation stakes are faintly visible in the area around the instruments. See next image for detail.

Figure 3.  Northern Icefield instrumentation site at ~noon, looking toward Uhuru Peak on left skyline (2 km distant). This cloud pattern represents typical diurnal development, with convection to the south and west, and rising up the Western Breach.


Figure 4.  Detail of Northern Icefield surface near the AWS, with small nieves penitentes formed since the 2017 long rain season. About 35 cm of the ablation stake is exposed. Between the penitentes is new snow from the previous evening. Also note the area of dirty ice to the right of the stake; the character of all glacier surfaces on Kilimanjaro is spatially heterogeneous and varies tremendously from year to year.


Figure 5.  Rapidly shrinking, east-end remnants of the Northern Icefield, likely once part of an ice body shown in image #95, here.


Figure 6.  The view north from near Uhuru Peak. Northern Icefield in the background, still 40+ meters thick, and the Furtwängler Glacier (foreground); Reusch Crater sloping up to the right. The Furtwängler ice area is 32 percent less than it was just two years ago (Sep. 2015). See image #115 here for the same view in 2013.


Figure 7.  The remaining ice of the former Eastern Icefield, ~1.5 km distant to the northeast.


Figure 8.  Upper Deckens Glacier near Uhuru Peak, one remnant of the former Southern Icefield. Compare with image #33 here from 2009, when the Decken and Kersten Glaciers were still connected. The upper sections of these dirty south-side glaciers provide dramatic evidence for the processes of both sublimation and melt.


Figure 9.  The upper Rebmann Glacier, not far from Stella Point. The recent break-up here has been rapid, associated (in part) with marginal lake formation and drainage; note several areas of buried ice. On the right-hand side of the image, note how the ice stratigraphy more-or-less parallels the slope, yet the ablation surface is nearly horizontal. Selecting sites to obtain ice samples for age dating of these glaciers, or for ice core drilling, is not a trivial issue.


Figure 10.  Looking east from camp, just after sunset. One of the views which keeps us going back!

Thursday, September 14, 2017

Sep-Oct Fieldwork

It's time for another visit to the summit glaciers!

Final planning is underway for fieldwork during late September into October, and we anticipate finding dramatic changes since August of 2016. For example, measurements at the AWS indicate that the Northern Icefield surface is more than 60 cm lower than at the time of our 2016 visit - at a location where specific mass balance remained more-or-less neutral for ~ 5 years. With this much ablation (lowering), maintaining vertical towers is difficult, as the middle image below illustrates; by February 2017 the time-lapse camera frame was already leaning, and ablation has continued since then.

Our primary tasks during fieldwork will be to recover AWS data and service the instruments. Almost all towers will probably need to be reset, due to ablation of the glacier surface. We will spend time on both the Northern Icefield, and the south-side Kersten Glacier (see second image).

We will also visit our network of ablation stakes on the glaciers (4th image), updating height change measurements last made in August 2016. Many of these stakes will require resetting, which we do by drilling new holes into the glacier surface.

Finally, we will make observations and measurements at several sites where geothermal heat is causing basal melting, as shown in the lowermost image. Previously-located sites will be visited, and we will search for new ones.

Accompanying us at the summit will be Dr. Chang'a of the Tanzania Meteorological Agency and the IPCC (Intergovernmental Panel on Climate Change). We are looking forward to interesting discussions about Kilimanjaro climate and climate change in general, as we ascend the mountain, attend to the weather stations, and document ongoing glacier retreat.





Monday, June 5, 2017

Update for 1 June


As the long rains season ends, Kibo appears rather snowy from the south. The image above is an early-morning view from the Mweka area yesterday. Thanks once again to Simon Mtuy! On the summit glaciers, telemetry does not indicate any significant snowfall events within the past few weeks.

Thursday, May 4, 2017

Snow

The Northern Icefield surface has received badly-needed snow accumulation since mid-February, rising 20-25 cm to approximately mid-October 2016 height. In hindsight, it appears that a minimum height occurred on 18 February, just prior to the photographs posted in the entry below. An early March snowfall event of 15-20 cm was followed by a month of predominantly ablation. A mid-April event then brought new snow, followed by 5-6 days of accumulation up until yesterday and adding 13-14 cm more accumulation. Typically the long rains continue through May, which could partially mitigate impacts of the short rain failure.

Tuesday, March 21, 2017

The value of a photograph


Measurements from our Northern Icefield AWS are transmitted to us in near-real time via the Argos system, which has proven to be extremely reliable. Telemetry is especially valuable for stations such as Kilimanjaro, for safely conducting fieldwork at 5,700 m requires considerable time simply for acclimatizing. With access to data by telemetry, conditions on the glacier can be monitored remotely, which saves on logistical costs and aids in fieldwork planning.

The figure above illustrates one measurement provided by telemetry: changes in glacier surface height. Decreases in height are due to ablation, the combined impact of melting and sublimation. Height increases are due to snow accumulation. Over time, the plot reveals both seasonal fluctuations of Northern Icefield surface height, and the on-going thinning which has been underway for decades.

For the time interval since June 2015, the bimodal wet seasons are depicted in green (Vuli = 'short rains', typically November & December) and in blue (Masika = 'long rains', typically March-May). Red circles represent the times of fieldwork in September 2015 and August 2016, and a recent visit described below. On the figure, note the lack of accumulation during the 2016 short rains, discussed in prior blog entries. Without much snowfall to add mass and brighten the glacier surface, ablation resumed in January 2017 at a rate similar to the dry season; this is not normal!


The lack of 2016 short rain precipitation on Kilimanjaro was at least partially due to a temperature contrast between the eastern and western Indian Ocean - the Indian Ocean Dipole - depicted above. During the NH summer, high ocean temperatures in the east led to more evaporation and cooling of the moister atmosphere. Easterly airflow over the western Indian Ocean resulted in less convection and less moisture delivery over East Africa during the short rains. In addition to less snowfall on the glaciers, the IOD is contributing to drought and famine in East Africa to the north of Tanzania. With over 10 million people facing food insecurity or worse, the consequences are profound (e.g., see here).


Back on the Northern Icefield, an on-site image from the AWS has provided information which measurements cannot. The image above was sent by Thomas Lämmle, who is frequently on Kilimanjaro with his company "EXTREK-africa" (website and Facebook EXTREK.AFRICA). Thomas' photo confirms the extent of ablation over the past couple months following the failed short rains. With great relief, the AWS tower appears to have remained nearly plumb, despite slackening of the guy cables. Also visible in the image are 3 ablation stakes (within blue ellipses) whose heights have been measured upon every prior visit.

Compare Thomas Lämmle's image from last month with a similar perspective ~17 months earlier, in September 2015 (below). From measurements at the AWS and the ablation stakes, we know that there was little net change in surface height between Sep. 2015 and Aug. 2016. The top figure also reveals that there was indeed no net lowering between Oct. 2011 and July 2016 (see y-axis). Not coincidentally, the AWS tower last required resetting in 2011 - the previous IOD negative event which was also associated with severe famine in East Africa, claiming 260,000 lives (link here).

Combining AWS data with photogrammetric ablation stake measurements reveals a glacier surface lowering of 40-45 cm between Sep. 2015 and the end of last month. Thanks to this recent photograph, we know that the AWS remained vertical as March began. Hopefully the long rains will bring new accumulation, which is the critical control on surface ablation at the Northern Icefield.

Thank you, Thomas!