ALOS-2/PALSAR-2 Observation results on detachment of a large iceberg from Larsen-C Ice Shelf in Antarctic Peninsula.

Posted: Jul 25, 2017, 7:30 (UTC)
Updated: Aug 9, 2017, 7:30 (UTC)

Larsen is one of the huge ice shelves in Antarctica. Larsen-A and -B experienced the destructions in 1995 and 2002, respectively. Larsen Ice Shelf affects the ice loss in west Antarctica and its contribution to global sea level rise. Therefore, many glaciologists have paid much attention to their dynamics. On 12th July, 2017, a large iceberg separated from Larsen-C Ice Shelf, which is the expected weight of approx. one trillion ton, and the surface area is about 5,800 km2. Due to its size, ALOS-2 ScanSAR mode (Observation width: 350 km) is suitable for capturing the entire portion of the iceberg (Fig. 1).

Fig.1: Observation area by ALOS-2.

Fig.2: Color composite images acquired on 21st July 2017 (left) and 19th Aug 2016 (right). The rectangles show the areas in Fig. 3. (Click to view enlarged image)

Figure 2 shows the color-composite images (red: HV, green: HV and blue: HH polarization) observed by ScanSAR mode. Sea ice is seen in the right side on the image and the ice shelf is seen in the left side. The rectangular at the center of the image shows the area where the iceberg separated from the ice shelf. We can see a trace of crack on the ice shelf over 100 km from south to the red arrow in 2016 (right panel in Fig. 2). However, the crack is seen entirely on the ice shelf in 2017, which means the iceberg has been completely separated from the ice shelf (left panel in Fig. 2).
Fig.3: Enlarged images of the iceberg. (Click to view enlarged image)

Figure 3 shows the enlarged images of the iceberg. We can clearly confirm the crack on the ice shelf. This figure reveals that the size of the iceberg is about 50 km of the width and 150 km of the length. This huge iceberg detachment has a potential to accelerate ice speed on the inland ice shelf, which may enhance more iceberg detachment. Taking advantage of ALOS-2 that can obtain images regardless of weather and acquisition time, we can contribute to understanding of global environmental changes by monitoring Antarctic cryospheric variations. We are going to continue the observation by ALOS-2.

Update on Aug. 9, 2017

Interactive comparison of images on 4th August, 2017.
Interactive comparison of images on 21st July, 2017.
Fig.4: Interactive comparison of images on 4th August, 2017 and 21st July, 2017.
* Drag a slider over the image or click an arbitrary position in the images to compare the images.

Figure 4 shows an interactive comparison of the color-composite images (red: HV, green: HV and blue: HH polarization) observed on 4th August, 2017 and 21st July, 2017. The width of the crack between the huge iceberg and the ice shelf on 4th August became smaller than that in 21st July. We have considered that sea ice has moved from the sea side toward the ice shelf, which pushed the huge iceberg. We can also see movements of some tiny icebergs in the figure (red arrows in Fig 4).