Glacial Till

Download PDF

What is Glacial Till?

Bookmark added to your notes.
View Notes

Glacial till is the deposition of sediment by a glacier. It overlaps glacier forefields, can be assembled to create moraines and other glacier landforms, and is omnipresent in glacial environments. It contains a very distinctive composition which typically appears from the fact that glaciers not only grind rocks, fragmenting them into fine, small pieces but they also take off large chunks of rock. This reflects that glaciers transport everything from big boulders to small grains smaller than sand.

What is a Till?

till is any substance laid down directly or revamped by a glacier. Essentially, it is a mixture of rock fragments and gibber stones in a fine-grained muddy or sandy matrix. The absolute composition of any specific till, however, depends on clay content, boulder size and their blend. However, in glacial landform, the type of deposition is called lodgment till. 

Types of Glacial Till

There are different types of glacial sediment usually categorized by whether they are transported on, within, or under the glacial ice. The primary types of sediment in a glacial environment are defined as below.

  1. Supraglacial (on top of the ice) and englacial (within the ice) sediments which skid off the melting front of a stationary glacier are able to create a ridge of unsorted sediments known as end moraine. The end moraine which reflects the farthest advance of the glacier is called a terminal moraine. Sediments carried and amassed by glacial ice are called till.

  2. Subglacial sediment (example is lodgement till) is a substance which has been eroded from the underlying rock by the ice, and is shifted by the ice. Supraglacial sediments are principally extracted from freeze-thaw eroded substance that has fallen onto the ice from rocky slopes above. These sediments create lateral moraines and, where two glaciers meet, medial moraines.

Glaciated Till

The sediments generated by glacial grinding are quite distinctive. Glacial till consist of sediments of every size, from minute particles smaller than a grain of sand to huge stones, all jumbled up together.

These sediments and rocks are blended altogether in a jumble after they are deposited. On the contrary, rocks and sediments collected by rivers settle out as the water slows down the speed, so huge boulders are frequently dropped before small grains of sand. Instead of jumbling sediments of every size, rivers organize them in a manner that viscous glaciers cannot.

Glacial Flour

Glacier flour defines the component of glacier sediment which is way finer than sand. This substance contains similar consistency to flour, which is why for its name. Since this sediment is so fine, it is effortlessly transported by and suspended in water. It is that flour tiniest size of sediment (much smaller than sand) and is accountable for the milky, colored water in the rivers, ponds, and lakes that are nourished by glaciers. Glacier lakes consist of a large-scale of beautiful colors which appears as sunlight scatters when it hits sediment particles in the water.

Quick Facts

  • When a glacier melts, all of the sand, mud and rock that it was bearing get left behind. This mixture of sediment is what we call till.

  • Blocks of ice left behind in the till steadily melt developing depressions termed as kettle holes. These can fill with water creating kettle lakes.

  • An erratic is a boulder which has been carried a long way by a glacier. Erratics are different types of rock than the local bedrock.

  • Till might just be a meter or two thick or tens of metres thick based on how much residue was in the ice.

  • Several tills can get constructed if glaciers advance and melt a number of times.

  • The composition of till demonstrates the geology of the region the ice has flowed over. This typically implies that till from various parts of a massive glacier will contain different types of minerals and rocks.

  • At times precious minerals can be detected to their bedrock source.

  • Geologists compare maps that display where there are high concentrations of minerals like gold or platinum with maps that depict which direction the glacier shifted. This is what they call drift prospecting.

FAQ (Frequently Asked Questions)

Q1. Why is it a Till Called Boulder Clay?

Answer: Often till is referred to as boulder clay since it is majorly composed of clay, boulders of intermediate sizes, or a blend of these. The rock fragments are generally angular and sharp instead of being rounded, as they are deposited from the ice and have experienced minimal water transport. The boulders and pebbles may be faceted and stripe from grinding while lodged in the glacier. Some till deposition display constrained organization of the fragments: huge numbers of stones may lie with their long axes running parallel to the direction flow of the glacier. This could provide more appropriate and adequate information about flow direction than other glacial signals.

Q2. What are the Different Types of Till?

Answer: Although difficult to distinguish by how it appears, there are 2 types of till, ablation and basal. Ablation till has been transported or on or near the surface of the glacier and has let down as the glacier melted. On the other hand, Basal till has been carried in the base of the glacier and often laid down beneath it.

Q3. What are the Different Types of Glacial Till?

Answer: Glacial till is divided into 2 categories which are further classified into subdivisions. The two classifications of glacial till are:-

1. Sub Glacial Till

  • Subglacial melt out till: often develops within cavities

  • Lodgement till: lodged by the ice onto the substrate

  • Deformation till: deformed soft non-glacial sediments

2. Supra Glacial Till

  • Supra glacial melt out till: lateral and medial moraines are reflection of supra glacial

  • Flow till: from flow of supra glacial substance at the ice front

  • Sublimation till: not very common, forms only in extremely cold regions