For the above said calving event, based on a conservative estimation on a 200m retreat on a front of about 5 km, and a thickness of several hundreds of meters, say 500m, we have at least 0.5 km3 gone to the sea. Which means about half the volume of the Glacier Blanc ...
I'm glad you're working on this issue. It's always easier for people to get involved with something happening in their own back yard, and to places that they care about.
If you want to delve further, I can suggest a way you may be able to make an even better estimate. With the freely available program 'Google Earth', it is possible to overlay a bitmap image over a geographic region.
Further, if you obtain recent MODIS imagery from the NASA World View
site that Jim Hunt has pointed us to recently, you should be able to see Glacier Blanc in 3 dimensions. Then you can use the Google Earth measurement tool to obtain better estimates for the extent of calving.
As a nice by-product of your efforts, you will be able to fly around a 3-D Glacier Blanc and the Hautes-Alpes in a virtual Flight Simulator that comes built into every copy of Google Earth
Let us know how it works out, and have fun!