A few days ago our group went for a walk on the Sólheimajokull Glacier in Iceland. This glacier has been receding rapidly - well over a kilometer in the last four decades. It is one of 14 glaciers worldwide studied by Jim Balog in his extreme ice survey (extremeicesurvey.org - go there; it's amazing).
Our first view of the glacier
This is the view to our left when the picture above was taken. Observe the ridges in the hillside. Until the last few years the glacier filled this "valley" up to that level.
A closer view emphasizing the prior height of the glacier.
Embarking on a hike with crampons and ice axes in hand.
Ascending onto the glacier.
Note the cones of cinders. A nearby volcanic eruption in 2010 covered the glacier with a layer of cinders. Depressions, cracks and crevices were filled with the cinders. As the glacier melted from the top, these deep pockets of cinders became the pyramids you see.
In this broader view, you can see the melting edge and a glacial lake it is forming.
Cinder cones reach the edge of the glacier, as the edge itself melts away.
Cinder islands remain in the lake that forms.
In another area, melting water forms a waterfall,
A closer view.
Down below the glacier, you can find the sequelae of similar waterfalls.
Now let's look at a snow arch that must have been formed by a small river of water running through and enlarging it.
A detail of the ice on one side of the arch
Two details of the top
The view through the arch reveals the bottom of a waterfall that once brought water to it and, off to the left, a glimpse of a glacial lake.
This is the waterfall..
and its current pathway.
Now lets look at what used to be an arch over another river formed in the ice.
In this view, our guide is walking under the two remaining sides of the erode arch.
The arch was both formed and eroded by a river that grew from a trickle in a crack in the ice. Warm water originally from the surface trickled down into the crack enlarging it gradually into a river way.
These ice caves were formed the same way.
I hope these illustrations help you understand some of the less well known mechanisms of glacial erosion.