CELPIP Reading Part 3Reading for Information Practice

A. During warm periods, meltwater gathers in pools and streams on the upper surface of a glacier or ice sheet. Dark particles and low areas can encourage melting to begin earlier in some places than in others. Surface streams often follow shallow channels until they encounter a crack that directs water downward into the ice. This connection transforms water travelling in sunlight into part of a hidden drainage network below the surface. This combination helps explain why seasonal meltwater flowing across glacier surfaces cannot be understood from one feature alone or from one brief observation.

B. Flowing water enlarges a fracture by melting its walls and carrying heat farther into the surrounding ice. The opening may develop into a steep shaft called a moulin, which can extend through a great thickness of ice. A moulin is not drilled as a perfectly straight cylinder, because existing cracks and ice movement influence its route. Its entrance can migrate, narrow, or become abandoned as the glacier deforms and the supply of meltwater changes. For formation and effects of glacier moulins, relationships among these features matter because a change in one may influence several others within the same setting over time.

C. Water descending through a moulin may reach channels at the glacier bed and increase pressure there. Higher pressure can temporarily reduce friction between ice and rock, allowing part of the glacier to move faster. As efficient drainage channels expand, they can later carry water away and lower pressure beneath the same area. The effect on ice speed therefore depends on timing and on how well the subglacial drainage system is organized. Viewed together, details about movement of water beneath the ice connect visible characteristics with processes that are less immediately obvious to an ordinary observer at first.

D. In winter, reduced surface melting may leave some shafts empty, blocked, or covered by new snow. The next melt season can reactivate an old route or create a different opening in another location. Researchers map moulins with surface observations, instruments, and tracers that reveal where flowing water reappears. Direct exploration is hazardous, so much of the internal network must be inferred from measurements made at safer points. Within formation and effects of glacier moulins, the result is a system in which structure, timing, and local conditions remain closely connected throughout continuing development.

E. Not given in any of the above paragraphs.