2. Starter
• Describe the different ways by which material can be
transported by a glacier
• How can the characteristics of the material help in giving
us clues as to how it was transported
• Compare and contrast lodgement and ablation till.
• Describe how sub glacial moraines differ from marginal
moraines.
3. The Role of Meltwater
• As seen meltwater plays a vital role in erosion,
entrainment transportation and deposition
• It is also indirectly involved in the processes of:
• Plucking
• Abrasion
• However, it is pivotal in the process of basal sliding and
sub glacial bed formation
• The two main sources of meltwater are:
• Surface melting
• Basal melting
4. Surface Melting
• Contributes most of the supply
• Peaks in mid summer
• Only source of meltwater for cold glaciers
• Supraglacial streams form on the top
especially in the ablation zone, often fast
flowing and can plunge through
crevasses but more commonly a ‘moulin’
(Cylindrical tunnel like a pothole)
5. Movement through the Glacier
• As it moves it may re-freeze or contribute to more
melting
• It may then reach a subglacial supply
6. Basal Melting
• Normally occurs in warm based glaciers
• Flows under hydrostatic pressure
• Can excavate subglacial tunnels by cutting through
bedrock
• Emerges through portals (caves) at the glacier snout
7. Processes of Erosion
• Glacier streams behave similarly to normal streams away
from the glacier
• Within the glacier ‘fluvio-glacial’ streams operate
differently because of the high pressure and velocity
• It causes erosion of the bedrock by abrasion, and
chemical weathering of the glacier
• It can also lead to intense erosion as it exits the glacier as
during deglaciation ablation rates can be very high leading
to large discharge.
8. Processes of Deposition
• Meltwater deposits material subglacially, englacially and
supraglacially
• This material is called ‘Ice contact fluvio-glacial deposit’
• Where the material is deposited at or beyond the ice
margin it is known as ‘proglacial or outwash’
9. Characteristics of fluvio- glacial Deposits
• Proglacial material is generally sorted and stratified by
the action of the meltwater
• Whilst ice contact deposits tend to be unsorted and
unstratified
• Smoother and rounder
• Sorted horizontally
• as the larger material tends to be found nearer the glacier
snout
• Stratified vertically
• which reflects the annual/ seasonal sediment changes
10. Clast shape and Imbrication
• Clast shape
– The clast maybe more angular or show
evidence of rounding due to the processes of
attrition
• Imbrication
– The clast may have a preferred orientation
and dip caused by the strong currents
– Clasts are aligned in the direction of ice
movement and often dip upstream
• Sorting
– Seasonal variations in stream discharge sorts
the grains into layers of consistent size
THIS CAN BE TESTED IN THE FIELD
12. Landforms of fluvio-glacial
Deposits
• Description: Long Sinuous ridges on the valley floor
• Explanation Formed from material in subglacial
tunnels as supply of hydrostatic meltwater decreases
• Subglacial streams carry large amounts of rocks and
debris due to their high hydrostatic pressure inside
tunnels
• When the glacier retreats it is deposited at a
consistent rate and forms a ridge as shown. They are
also distinctive to glacial deposits as they are
stratified and sorted and often have distinct bedding
of the sediments
Ice contact Fluvio-glacial
13.
14. Kames
• Description An undulating
mound of Fluvio-glacial sand
and gravel deposited on the
valley floor near the glacier
snout
• Explanation: Formed as
meltwater streams emerge onto
the outwash plain or proglacial
lakes at the glacier snout, their
velocity suddenly falls and
sediment is deposited
• Kames form in zones of melting
ice such as crevasses, moulins
and larger cavities
• They are often sorted
• They are distinctive as they
have an irregular pattern as
compared to drumlins which
Ice contact Fluvio-glacial
15. Kame Terrace
• Description: A flat linear deposit
of Fluvio-glacial sand and gravel
deposited along the valley sides
• Explanation: During the summer
the valley sides radiate heat,
melting the edges of the glacier
and forming meltwater streams
which deposit sediment
• When the glacier retreats, the
sediment will fall to the valley floor
forming kame terraces
• They often have sorted sand and
gravel
Ice contact Fluvio-glacial
16. Outwash Plain (Sandur)
• Description: A flat expanse of
Fluvio-glacial sediment in front of
glacier snout (proglacial)
• Explanation: As meltwater streams
emerge from the glacier and enter
lowland areas, they gradually lose
energy and are deposited
• They are size sorted by the water
runoff of the melting glacier with the
finest materials, like silt, being the
most distantly re-deposited, whereas
larger boulders are the closest to the
original terminus of the glacier
• (This is also a good example of
braiding)
Proglacial Fluvio-glacial
17. Kettle Holes
• Description: Small circular
depression often forming a lake
in an outwash plain
• Explanation: As the glacier
retreats, detached blocks of ice
remain in the outwash plain.
• Meltwater streams flow over the
ice covering them in deposits of
Fluvio-glacial debris eventually
the ice melts and the debris
subsides to form a depression
which often then fills with
meltwater forming a lake
Proglacial Fluvio-glacial
19. Proglacial lakes
• Description: A lake formed in front of the
glacial snout
• Explanation: Formed either by the
damming action of a terminal or
recessional moraine during the retreat of a
melting glacier, or by meltwater trapped
against an ice sheet due to isostatic
depression of the crust around the ice
Proglacial Fluvio-glacial
20. Meltwater Channels
• Description: A narrow channel cut into
bedrock or deposits, either underneath
or along the front of the ice margin
• Explanation: Meltwater can erode deep
channels, even gorges as a result of
high hydrostatic pressure within the
glacier and their high sediment load.
• The have unique characteristics:
– Under hydrostatic pressure Under
hydrostatic pressure beneath the glacier
they are able to flow up hill and they are
often larger than post glacial streams
– Braiding of meltwater channels is common,
due to seasonal variations in discharge
Proglacial Fluvio-glacial
21. Material (Fabric)
• The till fabric is often moved into the direction of flow due
to be re-worked by the ice and basal meltwater this means
they can be tested in the field into the direction that the
rocks face
• This should highlight the direction that the ice flowed and
help with understanding the direction the glacier travelled.
• They following exercise will highlight this:
22. Turn to page 81 (Oxford)
• Using the data in figure 8 draw the following graphs
– Mean Sediment size against Distance from Snout
– Average sediment shape against Distance from Snout
• (This is two separate graphs)
• Analyze each graph and describe the relationships if any
seen
• Other than Student t test what other tests could be run on
these relationships?
7.10 is on page 299
7.5 is on page 303
23. N. America
• Position of the ice
sheets in North
America at 10,000 and
7,000 years before
present
• This allowed many fish
to cross drainage
divides