Deep Crack In A Glacier

Deep Cracks in a Glacier: A Window into Climate Change and Glacial Dynamics

Glaciers, majestic rivers of ice, are powerful indicators of our planet's health. Their slow, relentless movement sculpts landscapes and influences global sea levels. But these icy giants are increasingly showing signs of stress, with deep cracks – known as crevasses – becoming more prevalent and wider. Understanding these deep cracks is crucial for comprehending glacial dynamics, predicting future changes, and ultimately, assessing the impacts of climate change. This article delves into the formation, characteristics, and significance of deep cracks in glaciers, providing insights into this fascinating and increasingly crucial aspect of glaciology.

Introduction: The Formation of Crevasses

Crevasses are deep, gaping fissures that form in the surface of glaciers. They're not just superficial cracks; they can extend tens of meters deep, creating significant hazards for climbers and researchers. Their formation is primarily linked to the interplay between the glacier's internal stresses and its brittle nature. Unlike a liquid, a glacier's movement isn't uniform. Different parts of the glacier move at different speeds and in different directions, creating internal tensions. These tensions, exceeding the glacier's tensile strength (its ability to resist being pulled apart), result in fracturing.

Think of it like this: imagine a thick, slow-moving river of ice. As it flows down a slope, the ice closest to the valley floor experiences more friction and moves slower than the ice higher up. This differential movement creates shear stress – a force that tries to slide one part of the glacier against another. Similarly, the glacier might flow around a bend or over an uneven terrain, generating tension that pulls the ice apart. When these stresses overcome the ice's strength, a crevasse is born.

The depth and orientation of a crevasse depend on several factors, including the glacier's thickness, slope, flow rate, and the nature of the underlying bedrock. Crevasses are most commonly found in areas where the glacier's surface is undergoing significant stretching or tension. These areas are typically found on the upper parts of glaciers, where the ice is flowing downhill rapidly, or in areas where the glacier is curving or flowing around obstacles.

Types and Characteristics of Glacial Crevasses

Crevasses are not all created equal. They exhibit diverse characteristics, classified based on their orientation and formation process. Some of the most common types include:

• Transverse Crevasses: These are the most common type, running perpendicular to the direction of ice flow. They form in areas of extensional stress, where the glacier is stretching and thinning.

• Longitudinal Crevasses: These crevasses run parallel to the direction of ice flow. They are less common than transverse crevasses and often form in areas of compressional stress, where the glacier is being squeezed. They often develop in the middle of the glacier where the ice is moving fastest.

• Radial Crevasses: These crevasses radiate outwards from a central point, often found where a glacier is flowing out from a confined area, such as a cirque (a bowl-shaped valley).

• Marginal Crevasses: These crevasses form along the edges of a glacier, particularly where the ice is interacting with the valley walls. They are often caused by differential movement between the ice and the bedrock.

The size and depth of crevasses can vary dramatically. Some may be relatively small and shallow, while others can be hundreds of meters long and tens of meters deep, creating significant hazards for those venturing onto glaciers. The appearance of crevasses can also change over time, with some closing up and others widening or extending depending on the prevailing stresses and the glacier's movement. Furthermore, the crevasses can be partially or fully filled with snow and ice, making them particularly dangerous as their presence is not always immediately obvious.

Deep Crevasses as Indicators of Glacial Health and Climate Change

The frequency, size, and depth of crevasses provide valuable insights into the overall health and stability of a glacier. An increase in the number and size of deep crevasses can signal that the glacier is undergoing significant changes, often related to climate change. Several factors contribute to this:

• Increased Meltwater: Rising temperatures lead to increased surface melting and the formation of meltwater streams and ponds. This water can infiltrate the glacier, lubricating the base and accelerating its flow. Faster flow often results in increased stresses and the formation of more numerous and larger crevasses.

• Changes in Ice Thickness: A reduction in ice thickness, due to increased melting or decreased snowfall, can weaken the glacier and make it more susceptible to fracturing. Thinner ice is less capable of withstanding the tensile stresses.

• Changes in Snow Accumulation: Reduced snowfall can expose more of the glacier's surface to melting, further accelerating the processes described above. A decrease in snowfall also means less "rejuvenation" of the glacier's surface, leaving it more vulnerable.

• Calving Events: The calving of large chunks of ice from the glacier's terminus (the end) can induce significant stresses in the remaining ice, leading to the formation of deep crevasses. This is particularly relevant for glaciers terminating in water.

Studying Deep Crevasses: Techniques and Challenges

Studying crevasses is crucial for understanding glacial dynamics and predicting future changes. Researchers employ various techniques to monitor and analyze crevasses, including:

• Ground-based Surveys: This involves manually measuring the size and location of crevasses using surveying equipment. It is labor-intensive and can be hazardous.

• Aerial Photography and Remote Sensing: Aerial photography and satellite imagery provide a broader perspective on the distribution and evolution of crevasses across the entire glacier. This allows for larger-scale monitoring.

• Ground-penetrating Radar (GPR): GPR can be used to map the subsurface structure of the glacier, revealing the depth and geometry of crevasses that are not visible on the surface. This is essential for understanding the internal structure of the glacier.

• GPS and other Geodetic Techniques: GPS and other geodetic techniques can be used to measure changes in the glacier's surface elevation and movement, providing further insights into the processes that lead to crevasse formation.

However, studying deep crevasses presents significant challenges. The harsh environment, remote locations, and inherent dangers make fieldwork difficult and expensive. Crevasses themselves are hazardous, requiring specialized safety equipment and techniques. Furthermore, the dynamic nature of glaciers means that crevasse patterns can change rapidly, requiring constant monitoring and updates.

The Significance of Crevasse Research: Predicting Glacial Change and Mitigating Risks

Understanding the formation and evolution of deep crevasses is not merely an academic pursuit; it has significant implications for:

• Predicting Glacial Retreat: The information gained from crevasse research can help to improve models of glacier flow and predict how glaciers will respond to future climate change. This is vital for assessing the contribution of glaciers to rising sea levels.

• Assessing Glacial Hazards: Knowledge of crevasse distribution is essential for managing risks associated with glacial travel and mountaineering. Understanding the patterns of crevasse formation can help to identify hazardous areas and inform safety protocols.

• Understanding Ice Sheet Dynamics: The processes that lead to crevasse formation in glaciers are also relevant to the dynamics of larger ice sheets, such as those in Greenland and Antarctica. Research on crevasses can therefore contribute to a broader understanding of ice sheet stability and potential collapse.

• Improving Climate Change Models: The data collected from crevasse studies contribute to improving the accuracy of climate change models, which in turn enhances our ability to forecast future climate scenarios and their impacts.

Frequently Asked Questions (FAQ)

Q: Are all crevasses dangerous?

A: Not all crevasses are equally dangerous. Shallow, partially filled crevasses might be relatively easy to navigate with proper safety precautions, but deep, open crevasses pose a significant risk of fatal falls. The presence of hidden crevasses, covered by snow bridges, is particularly hazardous.

Q: Can crevasses close up?

A: Yes, crevasses can close up under certain conditions. If the stresses that caused the crevasse to form are relieved, the ice can refreeze and seal the crack. This is more likely to occur in smaller crevasses, while larger ones may remain open for extended periods.

Q: How are crevasses formed in ice shelves?

A: Crevasses in ice shelves form due to similar mechanisms as in land-based glaciers, but with added factors like ocean-induced melting and fracturing at the ice shelf front. Tensile stresses from the ice shelf's movement and variations in thickness can lead to crack formation and propagation.

Q: What is the difference between a crevasse and a moulin?

A: While both are features found on glaciers, a crevasse is a surface crack formed by tensile stress, while a moulin is a vertical shaft that forms when surface meltwater penetrates the glacier's surface, often through crevasses.

Conclusion: A Continuing Story of Ice and Change

Deep cracks in glaciers are compelling visual manifestations of the complex dynamics governing these icy giants. Their formation is a delicate balance between internal stresses within the glacier and the ice's tensile strength. As climate change accelerates, the frequency and size of these deep cracks are increasing, serving as stark reminders of the significant changes our planet is undergoing. Continued research into crevasses is not just crucial for understanding glacier behavior; it is essential for predicting future changes, mitigating risks, and ultimately, for understanding the impact of climate change on our planet. The study of these deep fissures offers a window into the intricate world of glaciology, a window that, unfortunately, reveals a story of increasing instability and the urgent need for action.