Glacial deposition creates distinctive landforms and contributes to glaciated landscapes

Glacial Deposition and Debris

2.8 Glacial deposition creates
distinctive landforms and
contributes to glaciated landscapesGlacial debris
. Once rock has entered the glacial system and is
being transported, it is classified into three kinds of
debris:

• Supraglacial
• Englacial
• subglacialIce
  Surface
  debris layer
  Bedrock
  :

Debris
Direction of debris movement
0
O
Englacial flowlines
Equilibrium lineErratics
. The presence of large boulders known as glacial
erratics, so called because they are different tock
type to the bedrock they 'sit' on, testifies to the
sheer scaled of the ability of glaciers to transport
enormous quantities of rock over great distances.

• Example: Erratics from Scandinavia have been
  found in the boulder clay/till of Northumberland,
  Durham and Yorkshire, confirming the presence of
  the continental ice sheets from ScandinaviaDeposition
  How would a glacier deposit what it is carrying?
  Lodgement = this occurs
  beneath the ice mass when
  subglacial debris that was
  being transported becomes
  'lodged'. Lodgement occurs
  when friction between the
  subglacial debris and the bed
  becomes greater than the drag
  of the moving ice.
  Ablation = this process
  refers to debris being
  dumped as the glacier
  melts and thaws. It can
  include supraglacial and
  en glacial material, as well
  as subglacial material.Task - processes of glacial
  deposition
  Lodgement
  This process occurs beneath the
  ice mass when subglacial debris
  that was being
  transported
  becomes 'lodged' or stuck on the
  glacier bed.
  It is commonly associated with
  glaciers carrying huge loads of
  debris and where the glacier is
  very slow moving.
  This occurs if high meltwater
  content causes the glacial debris
  to creep/slide or flow during
  deposition
  Flow
  Less common process associated
  with weak underlying bedrock,
  whereby these sediments are
  defined by the movement of the
  glacier
  Deformation
  This process refers to debris
  being dumped as the glacier
  melts and thaws. It can include
  supraglacial
  and
  englacial
  material, as well as subglacial
  material
  AblationAll of these processes produce different till or boulder clay
  Lodgement till is more rounded
  Ablation till is more angular
  Lodgement till has a more rounded clasts
  because of the grinding that occurs at the
  ice bed interface
  Ablation till consists of more angular clasts
  as they are not ground down, and also the
  matrix is of larger-sized material and less
  compact.Glacial Deposits /
  SedimentClast Shape
• Clasts (rock
  fragments) can be
  angular or show
  evidence of rounding
  . Roundness = how
  smooth / sharp edges
  of clasts are
  . It depends on how
  much the clasts move
  and therefore erode
  through attrition
  high
  sphericity sphericity
  low
  very
  angular
  angular
  sub-
  sub-
  angular rounded rounded
  well
  roundedSediment Fabric
  . How the clasts are
  organised?
  · Orientation of clasts
  Do all the long axis point the
  same way?
  . Clast or Matrix supported
  Are the clasts in contact with
  and support each other?
  Clast Support
  Matrix Support
  · Imbrication
  An imbricated fabric is when
  the clasts are all stacked (like
  roof tiles or fallen dominoes)
  in the direction of flow.
  Current
  flowWhich sediment has an
  imbricated fabric?
  A
  B
  current
  @1998 Encyclopaedia Britannica, Inc.Stratification
  · Stratified sediment is divided into different layers.
  · Unstratified sediment is not!
  · Graded sediment has a layer of largest particles at
  the bottom with layers of fine particles on top.Sorting
  · What is sorting?
  · Sorting is the range of grain or clast sizes in the
  sediment.
  . Very well sorted sediments - grains all the same size
  . Very poorly sorted sediments - grains with a wide
  range of sizes
  very well
  sorted
  well
  sorted
  moderately
  sorted
  poorly
  sorted
  very poorly
  sorted
  Chart
  SortingLithology (the study of the general
  physical characteristics of rocks)
  . Are only local rocks present or erratics too?
  · Erratics are rocks which are foreign to the drainage
  basin.Drift
  (General term for all sediment
  deposited as a result of glacial
  processes)
  TILL DEPOSITS
  Deposition by glacial ice
  (old term = boulder
  clay)
  FLUVIO-GLACIAL
  DEPOSITS
  Deposition by meltwater
  (old term = outwash)Till Deposits
  Sketch
  Clast (rock
  fragment)
  B
  Rock flour
  (mainly
  clay)Sketch
  Fluvio-glacial Deposits
  Sand and
  gravel layer
  deposited
  in autumn
  Silt layer
  deposited
  in winter
  Pebble
  layer
  deposited
  in Spring &
  Summer
  2nd Year
  1 YearFor till and fluvio-glacial sediment
  work out the characteristics!
  Characteristic
  Use your notes & diagrams to help you decide ???
  Clast Shape
  (1) Angular and subangular or rounded?
  Sediment Fabric
  (2) Long axis aligned in direction of flow (Yes or No?)
  (3) Imbrication (Yes or No?)
  (4) Matrix or clast support?
  Stratification
  (5) Stratified or unstratified?
  (6) Grading (Yes or no?)
  Sorting
  (7) Sorted or unsorted?
  Lithology
  (8) Local rocks only or erratics present?

· Look at Figure 2.29 on page 96 Pearson Edexcel
Book 1 and see if you got the answers right.Characteristic
Definition
Till
Fluvio-glacial deposits (outwash)
Clast Shape: Rounded
Explanation:
Process of attrition in meltwater makes
clasts more rounded.
Imbricated Sediment - Long axis of clasts
aligned with direction of river flow and dip
with top of clasts pointing downstream.
Clasts support each other (not in a matrix)
Explanation:
Clasts move into position of least resistance
to strong river flow currents
Stratification
(stratified,
unstratified and
grading?)
Sediment is divided into different layers
Layer of largest particles at the bottom
with layers of fine particles on top.
Unstratified clasts.
Explanation:
Rock debris is dumped
chaotically by the glacier as it
melts out
Clasts are stratified and graded.
Explanation: Preferential transport by rivers
mean larger stones are dropped firsts as
river energy falls. Seasonal variations in
meltwater result in high flows in summer
moving and depositing larger material. Low
flows in winter so only fine silts moved and
deposited.
Sorting
Range of grain sizes in the sediment. A
sorted sediment has a common grain size.
(ie all the b-axis measurements are
similar)
Unsorted
Explanation: Ice has enough
energy to transport a very
wide range of grain sizes from
fine rock flour to huge
boulders
Sorted
Explanation: Preferential transport means
rivers do not move larger material far and
mainly deposit sands and gravels
Lithology
Only local rocks present or erratics too?
Erratics are rocks which are foreign to the
drainage basin.
Both
Explanation: Glaciers can move
rocks over long distances
Both
Explanations: Fluvio-glacial rivers will carry
whatever material was in the glacier
Clast Shape
(degree of
roundness)
Sediment Fabric
(Clast
orientation,
support and
imbrication)
Clasts (rock fragments) can be angular or
show evidence of rounding. Roundness
refers to how smooth or sharp are the
edges of particles. It depends on how
much the clasts move and therefore
erode through attrition
Orientation of clasts (Do all the a-axis
point the same way?)
Clasts in contact with and support each
other or are contained and supported by
a matrix of smaller particles eg sand, silt
or clay.
An imbricated fabric is when the clasts
are all stacked (like roof tiles or fallen
dominoes) in the direction of flow. The
clasts lean against each other with the
top of the clasts pointing downstream.
Clast Shape: Angular and
subangular
Explanation:
Clasts are frozen into ice
limiting their movement so
less attrition
Clasts (rock fragments) in a
clay matrix.
Long axis of clasts aligned in
direction of ice flow.
Clasts usually horizontal
rather than dipping
BUT in push moraine (see
later notes) imbrication occurs
as clasts dip.
Explanation:
Clasts move into position of
least resistance to ice flowNext lesson
Glacial Sediments (DRIFT)

Glacial Deposits and Landforms

Till and Fluvio-glacial Deposits

Glacial Deposits
Till (Boulder Clay)
Directly deposited by ice,
unsorted and unstratified

1. Landforms of Glacial
   Deposition
   Erratics
   Drumlins
   Moraines - lateral
   - recessional
   - terminal
   - medial
   - push
   Till Plain
   Fluvioglacial Deposits
   These deposits are sorted
   and stratifed by the action
   of meltwater

1. Landforms of Fluvioglacial
   Deposition
   Kames
   Kame Terraces
   Kame Deltas
   Eskers
   Kettle Holes
   Braided Streams
   Varves
   Outwash Plains (Sandur)Landforms of glacial deposition
   · The term moraine is used to refer to an
   accumulation of glacial debris, whether it is
   dumped by an active glacier or left behind as a
   deposit after glacial retreat.Lateral moraines
   Medial moraines
   Push moraines
   Ice contact
   depositional
   features
   Drumlins
   Terminal Moraines
   (end)
   Recessional moraines
   Lodgement till
   Lowland
   depositional
   features
   Ablation till
   Till plainsIce contact features:
   Moraines can be put into two broad categories:
   Moraines formed beneath the glacier (subglacial)
   Moraines formed along the margins of a glacier (ice-
   marginal)Ice marginal moraines
   Label the diagram with the following moraine types:
   · Lateral moraine
   · Medial moraine
   · Recessional moraine
   · Terminal moraineLateral moraine
   Lateral
   Moraine
   Lateral
   Moraine
   Medial MoraineMedial moraineLateral moraine
   Recessional moraine
   Terminal morainePush moraine
   L
   retreat
   moraine
   1
   advance
   pushing
   moraine
   ILateral moraines
   Medial moraines
   End moraines
   Terminus of
   glacier
   Recessional
   moraine
   Ground
   moraine
   Terminal
   moraine
   Outwash

· https://timeforgeography.co.uk/videos-
list/glaciation/glacial-deposits-types-moraine/Sub glacially formed moraines :
Drumlins
Wisconsin (Green Bay Lobe) DrumlinDrumlins - the unsolved mystery?
Drumlins are typically between 10m to 50m high and between 200m and 2000m long.
They usually occur in swarms which are referred to as 'basket of eggs topography'. They
are typically found in lowland areas.
Direction of ice flow
Stoss
Lee
Section
Plan
"Basket of eggs" topography
Elongation ratio = Length
WidthDrumlins:
. Are lined up parallel to the direction of ice flow
. Have their blunt end facing into the ice-flow
direction, and their tapered end facing downstream
of the direction of ice flow
· Are typically 100-2000m long and 50-600m wide
· Are usually under 50m high
. Are made of glacially deposited sediments,
although some have a rock core.Formation of drumlins?
. The formation of drumlins is not fully understood.
. One theory suggests that a drumlin is formed by
deposition in the lee of a slowly moving obstacle.
The obstacle of bedrock, or thermally frozen
material, forms the core of the drumlin and ground
moraine is plastered round it.
. The Shaw theory suggests that all drumlins, even
rock core drumlins, were formed by subglacial
meltwater in flood causing irregularities to form in
the river bed which were subsequently moulded into
drumlins and streamlined by the advancing ice.