Glacier terminal was over Sentinel Rock in the 1890's and at the present carpark as recently as about 1920. Glacier road extended further up the valley prior to I984. A big flood washed it out and it hasn't been reinstated. Successive layers of snow are compressed into hard ice in the Neves. Rate of ice flow depends on steepness of valley.
Ice keeps on flowing down-valley regardless of whether the glacier is advancing or retreating.
These are usually caused by extra snow falling in the neve on a short term basis. Fox has gained about 5OOm. Fox was named after William Fox, Premier of New Zealand in the 1860's. Haast was the first to explore the terminal of the Franz in the 1860's, but the area was not fully surveyed until Charlie Douglas did so in the 1890's. Tom Fyfe, Jack Clarke and George Graham on Christmas Day 1894.