, and there are probably only about 30 glaciers in thehe world t that e bebeen monitored for mass balale for 10 or morere yearsrs. >> a glacier exists here because snow that falls in the winter does not melt completely in the summer. the relative amounts of snowfall and melt represent this mass balance. like a positive bank account, a positive mass balance indicates s that the glacier is growing. on the flip side, if the glacier has less snowfall and more melt, the glacier becomes smaller. so how have generations of scientists come to grips with the estimation of the health of this 3,900-square-kilometer ice sheet? they dig. a lot. by digging many pits like these, scientists like dr. jason amundson calculate how much melted ice is flowing into the ocean. >> when the glaciers are actually in retreat, the one thing they do is they contrtribe to sea level rise, but they also affect atmospheric circulation patterns, which propagates downstream. it affects other things. the changes in the amount of freshwater runoff into the ocean, which will affect the ocean properties, which could afaffect