Brady Glacier lies in Glacier Bay National Park and Preserve, flowing from the Brady Icefield at 11,942 feet (3,640 m) in the Fairweather Range of the Saint Elias Mountains to Taylor Bay on Cross Sound’s north shore, about 139 miles (224 km) southeast of Yakutat and 32 miles (52 km) west of Gustavus, Alaska. The largest ice stream in the Fairweather Range, it stretches 32 miles (52 km) and covers 126,518 acres (51,200 ha). Sharing its accumulation area with the Reid and Lamplugh glaciers, it flows south and terminates above sea level in an outwash plain and tidal delta 3.7 miles (6 km) north of Taylor Bay. Taylor Bay, 3.4 miles (5.5 km) wide, extends northwest from Cross Sound for 4.5 miles (7 km) to the mouth of the Brady River. It was named by William Healey Dall of the US Coast and Geodetic Survey, possibly for H.C. Taylor of the US Navy in command of the SS Hassler, the hydrographic survey ship used in Cross Sound at that time. That same year, the survey named Brady Glacier for Reverend John G. Brady, a missionary who later governed the District of Alaska (1897–1906) before resigning amid fraud allegations linked to the Reynolds-Alaska Development Company. Glacier Bay’s topography results from the collision of the North American and Pacific plates. The Fairweather-Queen Charlotte Fault cuts its western edge and has guided the northwest movement of the Pacific Plate and Yakutat Microplate for over 50 million years. As the Pacific Plate is forced beneath its North American counterpart, fragments of island arcs, seafloor, and continental margin are scraped off and accreted. The peninsula between Taylor Bay and the Pacific comprises mainly the Chugach terrane. Extending from the western Alaska Peninsula to Southeast Alaska, it is composed of graywacke and siltstone that become increasingly metamorphosed northeastward. Beneath Brady Glacier, the Tarr Inlet suture zone marks the boundary between the Chugach and older Alexander terrane, whose rocks—over 500 million years old—were displaced from an equatorial region about 100 million years ago.

During the Last Glacial Maximum the Cordilleran ice sheet covered southeast Alaska and extended onto the continental shelf. It began retreating about 20,000 years ago as the Fraser Glaciation ended, eventually leaving most of the region ice-free. Periodic advances occurred during the Holocene—the most recent in the Little Ice Age, when cooling stretched from the 16th to the mid-19th century. Glaciers advanced until Glacier Bay was completely blanketed by the Glacier Bay Icefield; around 1770 the ice front began its retreat. These shifts highlight the dynamic interplay between climate change and glacial activity. Glacier Bay’s glaciers have been documented since 1794, when Captain George Vancouver visited. A survey party led by Lieutenant Joseph Whidbey recorded that the southern terminus of the Glacier Bay Icefield lay in Icy Strait. A submarine terminal moraine indicates the terminus extended into Icy Strait and bordered Lemesurier Island between 1725 and 1794. Vancouver sailed into Taylor Bay and observed Brady Glacier as a calving tidewater glacier. Sometime in the 1800s the glacier ceased calving and advanced about 5 miles (8 km)—a likely example of a tidewater glacier cycle in which an advance follows a change from tidal to non-tidal status. During the late 19th century the glacier receded, building the outwash plain that now separates it from Taylor Bay. Between 1926 and 1977 the plain expanded by more than 2.5 miles (4 km) and over 4,942 acres (2,000 ha). Compared with other glaciers in Glacier Bay National Park, Brady Glacier’s terminus has remained remarkably stable while gradually constructing its outwash plain. Yet this apparent stability conceals substantial thinning. Measurements from 1995 to 2000 documented an annual loss of 0.12 cubic miles (0.52 cubic km) of ice, and thinning along the terminus and margins has led to the formation of several ice-marginal lakes. These findings underscore the importance of considering both glacier extent and thickness when assessing glacial change.

Glacier-dammed lakes and their outburst floods can inflict severe downstream damage and alter glacier dynamics. The largest, most hazardous lakes form in ice-free tributary valleys blocked by active glaciers, while smaller lakes appear in alcoves along glacier margins or in depressions where tributary glaciers converge; most occur in the lower reaches. Once isolated, these depressions fill with meltwater and runoff until they overflow a bedrock saddle or trigger a self-dumping process, often reaching depths that destabilize the dam. Outburst floods can devastate infrastructure and reshape river channels. Lake failure may begin when a channel forms under, through, or over the ice. Causes include slow plastic yielding under hydrostatic pressure, floatation that lifts the dam, crack propagation from glacier flow combined with high pressure, drainage through preexisting channels at the ice–rock interface, overflow along the dam margin, subglacial melting from volcanic heat, and seismic weakening. These mechanisms, acting singly or in combination, can rapidly undermine the dam’s integrity. Once a leak forms, melting quickly enlarges the breach. Brady Glacier’s main terminus has remained relatively stable for 130 years. Yet between 1948 and 2000 its margins retreated up to 1.2 miles (2 km) and down-wasted up to 404 feet (123 m) near ten large ice-dammed lakes—six subaerial, four subglacial. In seven cases, its calving margin exceeded 0.6 miles (1 km). These lakes, along with numerous smaller ones, range from new or emergent to stable, non-draining or periodically draining. This variability reflects the complex interplay of climatic conditions and glacier mechanics. Calving margins of glacier-dammed lakes resemble those of tidewater glaciers. Once in equilibrium, climatic perturbations can thin tidewater glaciers, causing loss of grounding on stabilizing shoals and triggering calving that outpaces replenishment, sometimes leading to catastrophic retreat. Such dynamics underscore the hazards posed by ice-dammed lakes and the need for ongoing monitoring. Monitoring these systems is critical to mitigating risks and understanding glacial behavior. Read more here and here. Explore more of the Brady Glacier and Taylor Bay here: