Effective pressure in subglacial drainage
= Effective pressure in subglacial drainage
{title2=$N=p_i-p_w$}
Effective <pressure> is <ice>-overburden <pressure> minus <fluid pressure>[water pressure] beneath the <ice>. It controls creep closure of channels and cavities; smaller positive $N$ weakens that closure and favors separation of <ice> from bed obstacles. It is therefore central to both <basal sliding> and <subglacial drainage>.