Page 288 - Ultimate Visual Dictionary (DK)

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

Glaciers

A VALLEY GLACIER IS A LARGE MASS OF ICE that forms on land and moves slowly
downhill under its own weight. It is formed from snow that collects in cirques
(mountain hollows also known as corries) and compresses into ice as more and
more snow accumulates. The cirque is deepened by frost wedging and abrasion
(see pp. 282-283), and arêtes (sharp ridges) develop between adjacent cirques.
Eventually, so much ice builds up that the glacier begins to move downhill. As the
glacier moves it collects moraine (debris), which may range in size from particles
of dust to large boulders. The rocks at the base of the glacier erode the glacial
valley, giving it a U-shaped cross-section. Under the glacier, roches moutonnées
(eroded outcrops of hard rock) and drumlins (rounded mounds of rock and clay)
are left behind on the valley floor. The glacier ends at a terminus (the snout),
GLACIER BAY, ALASKA
where the ice melts as fast as it arrives. If the temperature increases, the ice melts
faster than it arrives, and the glacier retreats. The retreating glacier leaves behind its moraine and also
erratics (isolated single boulders). Glacial streams from the melting glacier deposit eskers and kames
(ridges and mounds of sand and gravel), but carry away the finer sediment to form a stratified
outwash plain. Lumps of ice carried on to this plain melt, creating holes called kettles.

VALLEY GLACIER
Medial
Lateral Meltwater Medial Suspended Horn moraine
moraine pool moraine erratic
Arête
Englacial (ridge)
Cave stream
Hanging valley Suspended
Melting erratic
glacier Stream
Ice margin
lake Snout
Waterfall
Terminal
moraine
Steep side of
U-shaped
Braided
stream valley
Boulder Terminal Meltwater Roche Lake
clay lake stream moutonnée
Push
moraine
POST-GLACIAL VALLEY
Roche Horn of
Collapsed Exposed moutonnée mountain
sediment Drumlin valley
floor Arête
Kame Esker Erratic (ridge)
terrace
Lacustrine
terrace
Post-
glacial Kame
stream delta
Kettle Terminal
moraine Terminal
Kettle moraine
lake
Steep side of
Outwash Boulder Kame Roche Outwash U-shaped Roche
terrace clay moutonnée fan valley moutonnée

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