UKH

For level 5/2nd year at university, I'm needing to measure the amount a glacier has retreated between 1985 and 2019, can anybody point me to a site which explains how one might come to a rough estimate on how far a glacier has retreated? 

Many Ta's.

Edit: This being done via mapping on google Earth, without taking into account things like mass balance, it's more to do with the difference between two different lines drawn on a map.

Crudest/simplest way is the change the date of the imagery on Google earth pro (your university will probably have a sub) and use the ruler tool along the centreline.

Ta. I guess the centre line would be halfway between the outer reaches/sides of the glacier? nb It is google Earth Pro we're using, my mistake in the OP.

French maps now now glaciers as in the 1970s and currently.  Interpolate??

A classmate took 3 measurements, being the highest, lowest, and a middle one, and has averaged the 3, it's only about 5 marks for the 'how did you measure the change' bit, so that seems good enough until/unless I come across another method, I have a few weeks to ponder if I want to be more complicated than that. 

https://vaw.ethz.ch/en/research/glaciology/glacier-monitoring.html#glamos

The Swiss have several projects, might be something useful amongst their site. 

I can't directly answer your question, but you might be interested in this site from David Archer of the U. Chicago which I made use of when I did one of his courses on Coursera a couple of years ago.

http://climatemodels.uchicago.edu

IIRC, a regular poster in this site is a glaciologist. Will rack my brains and try and remember who. 

Me (although maybe you meant someone else), which is why I got in a quick reply 😂 (I have also set this assignment and variations of it myself in the past). 
 

To the OP: the centreline is a little open to interpretation, but essentially yes, equidistant between the two margins. I’d also suggest that a really good student would consider the the method isn’t perfect, and do a few repeat measurements and estimate an uncertainty… A really good student would also look at thickness change over time using the profile tool 😉 

I assume you have been given a named glacier? Or do you have to pick one?

Thanks, yes we have a named glacier, I haven't looked yet into whether thickness can be examined via Google Earth Pro. The centre-line approach is quite vague seeming, almost tempted to take ten high and low points and find an average of them.

Many Ta's. 

some ranom thoughts...

could you do it via image processing and count the pixels in a standardised sized image? ie overlay the images.  I've no idea if this is practical given the tools

wont give depth but will give area.

i'd also want to pair up images for season and repeated images ir ot just one for 1985  and one for 2019 - if they exist !

Wont overlaying a contour map give a fair estimate of depth loss?

EDIT: perhaps not when channelled by vertical cliffs…

Doesn't really matter as long as you know the glacier's thickness before and after - it's more or less the same volume of ice going through the channel so it doesn't matter if the depth increases temporarily in the constriction.

this is beginning to sound like the thread about how much water is in Rutland Water!

I suggested doing a series of profiles based on contour information from the pre 1974 maps before flooding

The standard procedure here is to use the end of the balance year - I.e. when the glacier is at its minimum mass. Usually September in the northern hemisphere.

Yup, you can grab a profile from the DEM in GEPro, which is essentially what you are describing.

if it’s a Swiss glacier lots of them have very useful publicly available data on GLAMOS 

I'm possibly the other UKC resident glaciologist, unless there are others hiding out here (not unlikely, many of us climb).

Disappointingly enough, I can't give you a precise answer. I've not really worked with alpine glaciers, and trying to actually determine where a glacier ends from satellite imagery is often pretty ambiguous.

A good place to start would be the Randolph Glacier Inventory (https://www.glims.org/maps/glims). I've not used it myself but I believe they have an archive of glacier outlines for thousands of glaciers in a vector format you could import into Google Earth, GIS software or manipulate with a python package. They may have multiple outlines from different years for your glacier.

As ianstevens says, you want to measure along a centre line. I don't know if the RGI provides these. You could always plot one in Google Earth from the satellite view by delineating along some feature such as a medial moraine. There are more involved methods but something crude will probably suit the assignment fine.

Many thanks to yourself, and others too. 

I don't suppose you know what you'd call a circular and shallow indentation as a landform left behind by a glacier moving across it, too, and what process might create it?

It's not a deep feature, relative to it's size, but almost like a thin layer of rock, or paint for an analogy, has been picked away, but in bedrock.