What conditions cause glaciers to grow larger and advance?

Gravity and/or a downhill slope causes the glacier to advance. As it slides down, the glacier gathers more material such as snow and dirt, which cause the glacier to grow larger. 

Mexico has a host of environmental problems, including significant chemicalpollution  from factory discharges and waste dumping, but the main threat to itsbiodiversity  probably stems from  deforestation  and other natural habitat losses. forest habitat is lost for a number of reasons