Roncagli Glacier Retreat, Tierra del Fuego, Chile

The Cordillera Darwin in Tierra Del Fuego, Chile is a remote area that is notorious for stormy, cloudy weather that makes for only a few good satellite images. Roncagli(Alemania) Glacier is the focus of this post and is an update to a previous post. The glacier has a terminus adjacent to the Beagle Channe(BC) and a secondary terminus in Lago Martinic (LM), 5 km upglacier. Velocity profiles by Melkonian et al (2013) indicate the highest velocities directed toward the LM terminus, making this the primary terminus. They also found that the glacier thinned by 5-10 m along most of its length from 2000-2011. Here we examine Landsat imagery from 1997 to 2014.

Roncagli ge
Googel Earth image
In 1997 the BC terminus at the pink arrow is at a narrowing of the valley. The LM terminus is at the yellow arrow with two primary glacier branches encircling the nunatak at the red arrow. In 2000 the terminus positions are relatively unchanged with the LM terminus actively releasing icebergs into Lago Martinic. Upglacier a single area of bedrock is emergent through the glacier, purple arrow. In 2001 the BC terminus remains unchanged, the water level in LM has declined exposing more bare rock surfaces around the LM terminus. By 2008 the LM terminus has separated, both still ending in the lake, the lake again is at a full stage on the date of the imagery. The lake experienced periodic filling and draining episodes during the 1997-2008 period. There are now two upglacier areas with exposed bedrock now. By 2014 the BC terminus has retreated 1 km along the southeastern margin and 200 m along the northwest side. This retreat from the pinning point that restricted calving at the pink arrow, suggests further retreat will occur in the near future. Lago Martinic has largely drained. The LM terminus has separated into two tongues and the former nunatak is no longer surrounded by glacier ice, red arrow. The retreat at LM terminus is 1500 m on the west side, orange arrow, and 800-1000 m on the east side. Upglacier both areas of bedrock that are emergent are expanding, purple arrows, indicating the thinning observed by Melkonian et al. (2013). The continued upglacier thinning indicates reduced flux to the terminus and continued retreat. The degree to which Lago Martinic can refill is uncertain, MODIS imagery from late 2014 shows the lake is still not filled. I have not seen imagery indicating even a nearly full lake in the 2011-2014 period. The rate of retreat is less than on Marinelli Glacier to the north or Glaciar Steffen.
racongli 1997
1997 Landsat image
racongli 2000
2000 Landsat image
racongli 2001
2001 Landsat image

roncagli 2008
2008 Landsat image
racongli 2014
2014 Landsat image

Marinelli Glacier Retreat, Chile

Marinelli Glacier, Chile is the largest glacier of the Cordillera Darwin Icefield. This ice cap is in Tierra del Fuego, a region famous for cloudy, stormy weather. Fernandez et al. (2011) indicate that rapid retreat particularly since 1945 has led to high erosion and sedimentation rates. They also provide an excellent diagram of the glacier from three time periods. The glacier extended to the Little Ice Age-Neoglacial moraine at the red arrow. Koppes et al (2009) indicate a retreat of  13 km from 1960 to 2005, 300 m/year.

marinelli ge
Marinelli Glacier in Google Earth

marinelli ela
Cross section of glacier from Fernandez et al (2011)
Melkonian et al (2013) note widespread thinning with a peak on Marinelli Glacier. They also note frontal velocities of 7.5 m/day to 10.5 m/day from 2000 to 2011. They note approximately a 4 km retreat during this period and an average accumulation area ratio (AAR) of 38 (Melkonian et al, 2013). A non-calving glacier needs an AAR over 50 and typically over 60, since calving is an additional loss, calving glaciers typically need an AAR above 70 (Pelto, 1987).

marinelli velocity
Change in thickness on Marinelli Glacier from Melkonian et al. (2013)

Here we examine Landsat imagery from 1998 to 2014. In 1998 Marinelli Glacier had a main calving tidewater terminus and a land based terminus, red arrow. The tidewater terminus extends beyond the land based terminus. The land based terminus is connected to a tributary at the pink arrow. A tributary from the east is connected to the main glacier at the purple arrow. The yellow arrow is the 2014 terminus position. By 2001 the tidewater terminus has retreated up fjord of the land terminating terminus. The tributary on the west is still connected with the land terminating section of the glacier. By 2008 the main terminus has retreated exposing a new island in the center of the calving front. The land terminating section is now separated from the main glacier and with no supply of new ice will melt away, orange arrow. The tributary from the west is separated from the land terminus now at the pink arrow. The east tributary sill has a connection at the purple arrow to the main glacier. By 2014 the island at the main terminus has expanded in size as the glacier has retreated. The east tributary at purple arrow is separated from the main glacier. The isolated stagnant former land based terminus section between the red and orange arrows continues to melt away. The tidewater terminus of the glacier has retreated about 3.75 km from 1998 to 2014.  This is a rate of less than 300 m/year the long term average. The glacier will not stop retreating until its AAR rises and the calving margin reaches a pinning point. In this case there is no lateral pinning point apparent, hence it will have to be a rise in the elevation of the base of the glacier. The velocity and thickness change profile indicate such a location may exist 3-4 km behind the current calving front.  This glacier is retreating faster than the other glaciers of this icefield and is more in line with glaciers in the Southern Patagonian Icefield such as, Onelli Glacier, Glaciar Steffen, Glaciar Chico and Jorge Montt Glacier.

marinelli 1998
Landsat image 1998

marinelli 2001
Landsat image 2001

marinelli 2008
Landsat image 2008

marinelli 2014
Landsat image 2014

Alemania Glacier Retreat, Lago Martinic expansion-contraction, Chile

The Cordillera Darwin in Tierra Del Fuego Chile is a remote area. GLIMS (Glacier Land Ice Monitoring from Space) which has an inventory of glaciers showing at least size and boundaries, has nothing for this region in 2012. The USGS in their publication on South American glaciers just notes the lack of satellite imagery for assessing these remote glaciers. Chile is currently undertaking an inventory of these glaciers. The Alemania Glacier (Roncagli) is the focus of this post, the glacier can be seen from the Beagle Channel. The focus is not main terminus, but the terminus that ends in Lago Martinic (LM). In Google Earth imagery imagery this lake is trapped by the Alemania Glacier. There are two smaller glacier draining into the west end of the lake and Alemania’s secondary terminus ends in the lake. The red arrow points to the terminus, the green arrow to a nunatak near the Lago Martinic terminus and the yellow arrow to a developing nunatak upglacier, AT indicates the main terminus of the Alemania Glacier. The next three images are all from Landsat and indicate some spectacular changes from 2000 top image, 2008 middle image and 2011 bottom image. From 2000 to 2008 the Lago Martinic terminus of the glacier retreat 1300 meters, reaching the nunatak by 2008, this represents a significant expansion of the lake. In 2011 the terminus has retreated little but the lake has drained to an extent exposing the pink areas of the former lake bottom. In the future this maybe a lake that periodically fills in the Austral Spring and drains later in the Austral summer. The main terminus of the Alemania Glacier also exhibits a notably developing lake at the terminus compared to 2000, more on this below. The upglacier nunatak, yellow arrow, has also become more exposed indicating glacier thinning. A closeup of the main terminus of the Alemania indicates a 500 meter retreat of the east side of the glacier from the 2000 GE imagery to the 2011 Landsat imagery. The lake at the terminus has become significant, this should speed retreat in the near future. Though further south than the large Patagonia Icefields the glacier changes mirror those of the main icefields, Colonia, Tyndall, Gualas that are being intensively investigated by the Chilean Laboratorio de Glaciologia