The density of ice is 0.9167 g/cm<sup>3</sup> at 0 °C (under atmospheric pressure).

I know of two factors that may influence this (are there more?)

1) Pressure

The [glaciology faq (*Common Questions and Myths about Glaciers*)](http://ak.water.usgs.gov/glaciology/FAQ.htm) at the Alaska Science Center of the  U.S. Geological Survey (USGS) mentions for glacier depth:

> A good guess is that the ice thickness is about one-half of the surface width of the glacier. Although few glaciers have been measured, the measured thicknesses range from a few tens of meters for small glaciers to about 1,500 meters for the largest glaciers in Alaska.

Does the density of ice change significantly with depth?

[The Wikipedia article on ice](http://en.wikipedia.org/wiki/Ice) mentions the density of ice increasing slightly with decreasing temperature, and the different [phases](http://en.wikipedia.org/wiki/Ice#Phases) of ice under pressure, but nothing on density.

2) Inclusion of air

Googling for [pressure ice density](https://www.google.com/search?q=pressure+ice+density) the (my) first search finds [Density of glacier ice](http://www.igsoc.org:8080/journal/3/27/igs_journal_vol03_issue027_pg568-573.pdf) at the International Glaciological Society. This focuses on air in glaciers making the density *lower*, and concludes that at larger depths we reach that 0.92 limit.

What would be a good average to take?