Glacial Ice Cliff Collapse: Fits and Starts Explained

Yes, towering glacial ice cliffs can collapse in fits and starts, and this behavior is a key focus of cryosphere research. These cliffs, often hundreds of meters tall, do not fail as a single, sudden event; instead, they undergo repeated episodes of fracture, calving, and temporary stabilization, driven by a complex interplay of ice temperature, ocean melt, and structural stress. Understanding this stop-and-go collapse is essential for predicting how rapidly ice sheets like those in Greenland and Antarctica will contribute to sea-level rise.

What Are Glacial Ice Cliffs?

Glacial ice cliffs are the steep, often vertical faces of glaciers or ice sheets that terminate in the ocean or a lake. They form where ice flows off land and meets water, creating a front that can be tens to over a hundred meters high. Unlike a glacier’s gently sloping terminus, ice cliffs are unstable because the ice is thick, heavy, and under immense internal stress. The most famous examples are the tidewater glaciers of Alaska, the outlet glaciers of Greenland, and the floating ice shelves of Antarctica, where cliffs can tower above the waterline.

How Do Ice Cliffs Collapse?

Ice cliffs fail through a process called ice calving, which is the breaking off of chunks of ice from the glacier front. This is not a single, uniform event. Instead, it happens in a series of fits and starts:

• Crack formation: Stress builds as ice moves forward or as the ocean melts the submerged base. This stress creates surface and internal cracks (crevasses).
• Partial failure: A section of the cliff, often a block tens of meters across, breaks off and topples into the water. This can happen rapidly, but it’s a localized event.
• Retreat and stabilization: After a large calving event, the cliff face retreats to a position where it is temporarily more stable, often grounded on a shoal or where the ice is thicker and more resistant.
• Renewed stress: Over weeks or months, the glacier continues to flow forward, and the ocean continues to melt the underwater part, rebuilding the stress that leads to the next calving episode.

This cycle of stress accumulation → sudden failure → temporary stability → renewed stress is what gives ice cliffs their characteristic fits-and-starts behavior.

Why Do Some Cliffs Collapse Rapidly?

Several factors can accelerate the collapse cycle, turning a slow, episodic process into a rapid, near-continuous retreat:

• Ocean warming: Warmer water melts the submerged part of the cliff, undercutting it and removing the support that holds the ice above. This makes the cliff more prone to toppling.
• Ice thinning: A thinner ice cliff is less able to support its own weight, so it fails more easily. Thinning also reduces the buttressing effect of ice shelves, which normally hold back glaciers.
• Surface meltwater: Meltwater on the surface can pour into crevasses, widen them, and even drive them all the way to the bed, causing sudden, deep fractures.
• Ice fabric and temperature: Warmer ice is softer and more ductile, so it deforms rather than fracturing. Colder ice is more brittle and prone to sudden, explosive failure. The internal structure (fabric) of the ice, including the orientation of ice crystals, also influences how cracks propagate.

The Role of Ice Shelves and Buttressing

Many glaciers are held back by floating ice shelves—thick, floating extensions of the glacier. These shelves act like a cork in a bottle, slowing the flow of ice behind them. When an ice shelf collapses (as seen with Larsen B in Antarctica in 2002), the glaciers behind it suddenly lose this buttressing force. The result is a dramatic acceleration of ice flow and a rapid increase in calving, with ice cliffs collapsing in a series of large, episodic events. This is a classic example of how a sudden change in boundary conditions can shift a glacier from a stable, slow-calving state to a rapid, fitful collapse.

Measuring and Predicting Collapse

Scientists monitor ice cliffs using a combination of satellite imagery, ground-based radar, GPS, and oceanographic sensors. They track the position of the ice front over time, measure the height of the cliff, and record the frequency and size of calving events. This data feeds into numerical models that try to predict future behavior. However, modeling ice cliff collapse is notoriously difficult because it involves processes that occur on very small scales (crack formation) but have consequences on very large scales (entire glacier retreat). The “fits and starts� behavior makes predictions especially challenging, as a glacier may appear stable for years and then suddenly undergo a series of rapid collapses.

Why This Matters for Sea-Level Rise

The collapse of ice cliffs is a major source of uncertainty in sea-level rise projections. If glaciers like those in West Antarctica collapse rapidly, they could add significantly more to global sea levels than current models suggest. The “marine ice cliff instability� hypothesis posits that once an ice cliff becomes tall enough, it cannot support its own weight and will fail catastrophically, leading to a self-sustaining retreat. This is a contentious idea, and the actual behavior—whether cliffs collapse in a slow, episodic manner or in a rapid, runaway fashion—is a critical unknown. The fits-and-starts behavior observed in many glaciers provides some hope that collapse might be more gradual than the worst-case scenarios, but it also means that sudden, unexpected accelerations are possible.

Frequently Asked Questions

Can ice cliffs collapse without warning?

Yes, individual calving events can happen without much warning, sometimes within minutes. However, the overall pattern of collapse is usually preceded by visible signs like the formation of large crevasses, increased seismicity (icequakes), and a thinning of the ice. Scientists can often identify periods of heightened instability, but predicting the exact moment of a specific calving event is not yet possible.

What is the tallest ice cliff ever recorded?

Ice cliffs are typically between 30 and 100 meters high, but some can be much taller. In Greenland, cliffs at the front of Jakobshavn Isbræ have been measured at around 100 meters. In Antarctica, ice shelves can have fronts that are over 50 meters high, but the tallest cliffs are found where ice streams meet the ocean, and these can be over 100 meters. The theoretical maximum height for a stable ice cliff is a subject of active research, with estimates ranging from 100 to 200 meters depending on ice temperature and fracture mechanics.

Do ice cliffs collapse faster in summer?

Yes, in many regions, calving rates increase during the summer months. This is because warmer air temperatures cause more surface melting, and the meltwater can enhance fracturing. Warmer ocean water in summer also increases submarine melting, which undercuts the cliff. However, in Antarctica, the seasonal signal is less pronounced because the ice is colder and surface melting is limited, but ocean-driven melting still varies seasonally.

Is an ice cliff collapse the same as an iceberg breaking off?

Yes, they are essentially the same process. An ice cliff collapse is a type of calving event. The term “collapse� is often used for larger, more dramatic failures where a significant portion of the cliff face breaks away, while “calving� can refer to any size of ice chunk breaking off, from small bergy bits to massive tabular icebergs.

Can ice cliffs collapse in a chain reaction?

Yes, this can happen. When a large section of a cliff collapses, it can remove support for adjacent sections, triggering a series of failures. This is sometimes called “progressive calving� or “domino-style� collapse. This is more likely to occur when the ice is heavily fractured and under high stress. Such chain reactions can lead to very rapid retreat of a glacier front over a short period.

Related

• MKV Converter: What It Does and How to Use One
• How to Choose a Marine Conservation Organization
• Google Home Speaker Bricked? Fixes & What to Know