SR1 & SR2, the main player: the SWT
In the other world the SWT was an important but secondary actor, the MIS being clearly the main actor and it was necessary to start from it to analyze the SIS, in its entirety, including SWT.
The SWT was forced to turn 135° and was forced to turn, upstream, through the more western part of the SIS, and downstream, directly through the MIS. I remind you that this part of the SWT flow is completely floating and therefore not constrained by the seabed.
At the meeting between the SWT and the SIS along the right shear margin of the SWT, margin that I will call ESM (East Shear Margin) there were two forces that were exerted: the one due to the constraint to turn and the one due to the speed differential between the SWT and the SIS. These forces were not visible on the surface: not rifts. Indeed, the SIS was completely wedged and compressed between the SWT and the MIS.
There was a brief period of transition in which there was no longer direct contact between the SWT and the MIS, but only indirect contact by the Cork, which provided pressure on the SWT and the SIS. However, the SWT was no longer forced to turn 135°, but only 45°, and it had begun to increase its speed. However, the SWT was no longer forced to turn 135°, but only 45°, and it had begun to increase its speed.
In November I had measured a speed, at the calving front, for the fastest flow (east side of the SWT flow) and the result was 1.7km, to be compared with a "normal" speed of 1km (see attached picture). Even though the speeds at the calving front may be higher if there are rifts opening, as was indeed the case, the difference is significant enough and, in any case, the calculated speed at the ESM, which is lower relative to the flow, was 1.25km. This speed fell to 0.6km in the SIS south of Cork, in line with the speeds of other times.
For the rest the old way of working of the SWT and SIS was not yet upset.
But towards the end, following the Cork's shift, the pressure that the Cork exerted on the SIS quickly weakened: not only did it weaken, but it also shifted more and more to the SWT. And that's when SR2 appeared.
After the calving more MIS action on the SWT and even on the western part of the SIS, if not on the margin (we'll see that in another post).
And it is on this occasion that SR1 also opens up in the middle of the SIS and rapidly expands to the ESM as well. The fact that they both open in the middle of the SIS on the ESM side and extend to the ESM and that the most marked part is on the ESM side is the signature of the forces that generate them.
I attach:
> an image of the speeds indicated not only by color, but also by speed level lines, one line every 0.1km/y. I have added to this image:
>> the glacier and SWT shear margin notations
>> the current calving front (in pink)
>> the dividing line between SWT and TG (in yellow)
NB: As soon as possible I'll recalculate the speeds based on the most recent images, to check if there are already some new features.
click to zoom in
> an animation related to the ESM based on the Sentinel2 images of 07-03-2018, 02-11-2018, 20-02-2019, ESM 14-09-2019 and 16-03-2020 which shows that in the last months the ESM has moved east. That is to say, the MIS being far away, the SWT is starting to impose its laws
EDIT: In the interpretation of this animation take into account that the ESM is moving northwards
> an animation relative to SR2 with images between 27-12-2019, date of appearance of SR2 and 01-02-2020, the date of the last image before calving (5 images; twice click to animate and zoom in)
> an animation relative to SR1 and SR2 with images between 11-02-2020, first image after calving, and date of appearance of SR1 and 16-03-2020 the date of the last image (3 images; twice click to animate and zoom in)
And in the next post (limit of 4 images):
> A zoom relative to the first appearance of SR2 (27-12-2019)
> A zoom relative to the first appearance of SR1 (11-02-2020)
A post on an analysis of the forces exerted on the Cork2 will soon follow.