Landforms associated with different parts of an ice mass

Glacial landforms provide clues about the past presence and behaviour of glaciers. These features form in specific zones relative to the ice mass, creating distinctive landscapes through processes like erosion and deposition.

Subglacial areas

Subglacial areas lie directly beneath the ice mass. Their landscapes show a high concentration of erosional features, indicating the ice's presence.

Marginal areas

Marginal areas form at the edges of glaciers or ice sheets. These landscapes show evidence of the ice through their depositional features, formed by both glacial and fluvioglacial processes.

Proglacial areas

Proglacial areas are located in front of the ice mass. These landscapes show features created by meltwater and wind, with fluvioglacial depositional processes strongly influencing their shape.

Periglacial areas

Periglacial areas are cold regions near glaciers, often featuring permafrost (permanently frozen ground). These landscapes are shaped by weathering processes like freeze-thaw action, with ice movement and melting having minimal direct impact.

Scales of glacial features

Glacial features range in size, from tiny marks to landscape-dominating structures. Understanding their scale helps in identifying and interpreting them in the field.

Micro-scale features

Micro-scale features are the smallest, typically less than 1 metre in length.

Examples of micro-scale features:

• Striations

Meso-scale features

Meso-scale features are medium-sized, ranging from 1 metre to 1 kilometre in length.

Examples of meso-scale features:

• Roches moutonnées
• Drumlins
• Eskers
• Kettle holes
• Erratics

Macro-scale features

Macro-scale features are the largest, often dominating entire landscapes.

Examples of macro-scale features:

• Glacial troughs
• Corries
• Sandurs

Relict landscapes and reconstructing past glaciation

Relict landscapes preserve evidence of past ice cover, allowing us to reconstruct glacial history. These differ from active glacial landscapes, which are currently under ice.

Characteristics of relict landscapes

Relict landscapes show remnants of glacial features after the ice has melted. Analysing these helps determine the extent and nature of former glaciation.

Challenges in interpreting relict landscapes:

• Multiple glacial periods can overlay features, complicating analysis.
• Human activities, such as farming or construction, may alter or obscure natural landforms.

Inversion modelling and uniformitarianism

Inversion modelling involves studying remaining features to infer past glacial events. This relies on Hutton's principle of uniformitarianism, which states that processes observed today, like erosion and deposition, operated similarly in the past to shape landscapes.

Differences between upland and lowland glacial features

Glacial features vary by altitude, reflecting different dominant processes.

Upland areas:

• Located at higher altitudes, such as mountain slopes.
• Primarily characterised by erosional features.

Lowland areas:

• Found at lower altitudes, such as valley floors.
• Mainly characterised by depositional features.

Features indicating glacier direction

Certain glacial features reveal the direction of ice movement, helping reconstruct glacier flow paths.

Erratics

Erratics are boulders transported by ice and deposited far from their origin. Identifying their rock type traces back to the source area, indicating the glacier's direction of travel.

Drumlins

Drumlins are streamlined hills aligned with ice flow. Their orientation shows the glacier's direction: the steeper, taller end faces upglacier (towards the ice source), while the gentler, tapered end points downglacier.

Crag and tail landscapes

Crag and tail landscapes are aligned with ice flow, with the resistant rock outcrop (crag) facing upglacier and the deposited tail of sediment extending downglacier, paralleling the ice flow direction.

Corries

Corries are circular hollows that often face the same direction on a mountain slope, indicating the glacier's downslope route. However, when forming a pyramidal peak, corries may face multiple directions around the peak.

Features revealing glacier path, extent, and speed

Beyond direction, some features provide insights into a glacier's specific path, maximum extent, and movement speed.

Indicators of glacier path

Lateral moraines are ridges formed alongside the glacier, mirroring its path.

Indicators of glacier extent

Recessional and terminal moraines indicate the position of the glacier's snout or its furthest extent.

Indicators of glacier speed

Drumlin elongation ratio:

Drumlins' shape reveals ice speed. Longer, narrower drumlins suggest faster movement.

Formula for elongation ratio:

$\text{Elongation ratio}=\frac{L}{W}$

Where:

• L = Length of the longest axis
• W = Width at the widest point

A higher ratio indicates faster glacier flow, as rapid ice stretches the sediment more.

Till fabric analysis:

• This method examines the orientation and dip (angle of tilt) of elongated particles in till deposits.
• Analysing a large sample of till reveals the probable path and flow direction of the glacier, as particles align with ice movement.