The mass balance of a glacier, the term having been introduced by Elsberg et al. (2001) to distinguish the mass balance from the reference-surface balance, which is the balance the glacier would have
if the glacier surface geometry were fixed in time. Conventional balances are obtained when point measurements over a particular time interval are extrapolated to the glacier area and area-altitude distribution measured during the same time interval. Calculations of conventional balance require repeated mapping of glacier hypsometry at intervals appropriate to the rate of change of the surface geometry. However, maps are often re-calculated at longer time intervals, the reported balances being a combination of conventional and reference-surface balances. Conventional balances are relevant for hydrological applications because they represent the actual mass change of a glacier. Conventional balances are not simply correlated to variations in climate because they incorporate both climate forcing and changes in glacier hypsometry. For glacier/climate investigations the reference-surface balance is a more relevant quantity.
In plate tectonics, a convergent boundary or convergent plate boundary, also known as a destructive plate boundary (because of subduction), is an actively deforming region where two (or more) tectonic
plates or fragments of lithosphere move toward one another and collide and where crust is being destroyed. [Wikipedia]