“The extent of pre-Columbian land use and its legacy on modern ecosystems, plant associations, and species distributions of the Americas is still hotly debated. To address this gap, we present a Holocene palynological record (pollen, spores, microscopic charcoal, SCP analyses) from Illimani glacier with exceptional temporal resolution and chronological control close to the center of Inca activities around Lake Titicaca in Bolivia. Our results suggest that Holocene fire activity was largely climate-driven and pre-Columbian agropastoral and agroforestry practices had moderate (large-scale) impacts on plant communities. Unprecedented human-shaped vegetation emerged after AD 1740 following the establishment of novel colonial land use practices and was reinforced in the modern era after AD 1950 with intensified coal consumption and industrial plantations of Pinus and Eucalyptus. Although agroforestry practices date back to the Incas, the recent vast afforestation with exotic monocultures together with rapid climate warming and associated fire regime changes may provoke unprecedented and possibly irreversible ecological and environmental alterations.”
“Politicians have tussled for years over the fate of the Tongass, a massive stretch of southeastern Alaska replete with old-growth spruce, hemlock and cedar, rivers running with salmon, and dramatic fjords. President Bill Clinton put more than half of it off limits to logging just days before leaving office in 2001, when he barred the construction of roads in 58.5 million acres of undeveloped national forest across the country. President George W. Bush sought to reverse that policy, holding a handful of timber sales in the Tongass before a federal judge reinstated the Clinton rule.
“The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (Sørensen et al. 2018). We refer to this 5415 km survey as the ‘PROMICE perimeter’ (Fig. 1). Here, we assess ice-sheet mass balance following the input-output approach of Andersen et al. (2015). We estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice flux across the PROMICE perimeter.”
Mendenhall Glacier is the most visited and photographed terminus in the Juneau Icefield region. The glacier can be seen from the suburbs of Juneau. Its ongoing retreat from the Visitor Center and the expansion of the lake it fills is well chronicled. Here we document the rise in the snowline on the glacier that indicates increased melting and reduced mass balance that has driven the retreat. The change in snowline from 1984-2018 and the associated retreat are documented. The snowline as July begins in 2019 is already in the end of summer range.
Mendenhall Lake did not exist until after 1910. In 1948 it was 2.2 kilometers across, and by 1984 the lake was 2.7 km across. Boyce et al (2007) note the glacier had two periods of rapid retreat: one in the 1940’s and the second beginning in the 1990’s, both of which were enhanced by buoyancy-driven calving. The latter period has featured less calving, particularly in the last decade, and is a result of greater summer melting and a higher snowline by the end of the summer, which has averaged 1,250 meters since 2003 vs. 1,050 m prior to that (Pelto et al, 2016). In 2005, the base of the glacier was below the lake level for at least 500 m upglacier of the terminus (Boyce et al (2007). This suggests the glacier is nearing the end of the calving enhanced retreat. It is likely another lake basin would develop 0.5 km above the current terminus, where the glacier slope is quite modest.
The glacier in 1984 ended at the tip of a prominent peninsula in Mendenhall Lake. The snowline is at 950 m. In 1984 with the Juneau Icefield Research Program, we completed both snowpits and crevasse stratigraphy that indicated retained snowpack at the end of summer is usually more than 2 m at 1,500-1,600 m. The red arrow indicates a tributary that joins the main glacier, where Suicide Basin currently forms. In 2014 the snowline in late August is at 1,050 m. The terminus has retreated to a point where the lake narrows, which helps reduce calving. In 2015 the snowline is at 1,475 m. In 2017 the snowline reached 1,500 m. There is a small lake in Suicide Basin. In September 2018 the snowline reached 1,550 m—the highest elevation the snowline has been observed to reach any year. In Suicide Basin the lake drained in early July. In 2018 Juneau Icefield Research Program snowpits indicates only 60 percent of the usual snowpack left on the upper Taku Glacier, near the divide with Mendenhall Glacier. On July 1 2019 the snowline is already as high as it was in late August of 1984. This indicates the snowline is likely to reach near a record level again. The US Geological Survey and the National Weather Service is monitoring Suicide Basin for the drainage of this glacier melt filled lake. In 2019 the lake rapidly filled from early June until July 8—the water level increasing 40 feet. It has drained from July 8 to 16 back to it early June Level. The high melt rate has thinned the Mendenhall Glacier in the area reducing the elevation of the ice dam and hence the size of the lake in 2019 vs. 2018.
The snowline separates the accumulation zone from the ablation (melting) zone and the glacier needs to have more than 60 percent of its area in the accumulation zone. The end of summer snowline is the equilibrium line altitude where mass balance at the location is zero. With the snowline averaging 1,500 m during recent years, this leaves less than 30 percent of the glacier in the accumulation zone. This will drive continued retreat even when the glacier retreats from Mendenhall Lake. The declining mass balance is evident across the Juneau Icefield (Pelto et al 2013). Retreat from 1984-2018 has been 1,900 m. This retreat is better known, but less than at nearby Gilkey Glacier and Field Glacier.
This article originally appeared on the American Geophysical Union blog, From a Glacier’s Perspective.
It’s summertime in the Northern Hemisphere. And for those of us that are able, the summer months can mean time off from work and an opportunity to venture near or far on a vacation.
Glaciers lie on each of the world’s seven large landmasses, meaning, while they’re often located in relatively remote areas, one needn’t travel to the polar regions to observe the remnants of the last Ice Age—which makes them a popular vacation draw.
New Zealand has the Southern Alps. Glaciers are found in each of the seven Andean nations: Venezuela, Columbia, Ecuador, Peru, Bolivia, Chile, and Argentina. The mountains of the American West, as well as Alaska, host glaciers. And, of course, there are the alpine peaks of southern Europe and the iconic, albeit much more remote, mountains of the “Third Pole.”
A survey of photo sharing websites, such as Flickr, reveals the enduring allure of the world’s glaciers, particularly as climate change and the threat it poses to the longevity of the world’s cryosphere becomes more and more apparent.
And therein lies a paradox.
So-called last-chance tourism is driven by interest in visiting the landscapes that are vulnerable to rising temperatures and more frequent and more intense extreme weather events. Yet with greater interest in these places comes increasing threats to their sustainability, whether due to carbon-intensive airline travel or the consumer waste that results from a simple visit to the refreshment stand at a national park. A recent study even sought to quantify the amount of summer sea ice in the Arctic that melts with each metric ton of carbon emitted by an individual.
Individual consumer decisions won’t bring the world significantly closer to zero emissions as long as decisions about how energy is generated, what modes of transportation are available, and how consumer goods are produced—the largest sources of carbon pollution—remain largely in the realm of the public sector, that is society-wide.
Visiting glaciers can heighten one’s understanding of the massive forces bound up in Earth’s climate and geology, which, perhaps for many people, explains their seduction.
Here’s a view of some of the world’s popular glacier destinations through the eyes of recent visitors.
Just a short journey from Alaska’s capital city of Juneau, Mendenhall Glacier is the state’s most popular summer tourist destination, and arguably one of the most accessible glaciers in the world. Located in Tongass National Forest, Mendenhall is one of 38 glaciers that originate from the massive 1,500 square mile Juneau Icefield. From its origin to its terminus at Mendenhall Lake, the glacier stretches some 13.6 miles.
A strong tourism industry around Alaska’s glaciers provides the state with substantial economic benefits. It also gives visitors an opportunity to witness the effects of anthropogenic climate change.
Beyond the pristine beauty and temperate summertime weather in Alaska, so-called “last chance tourism” is a huge motivation for visitors, who wish to marvel at immense blocks of blue and white ice as well as Mendenhall’s famous ice caves before they melt.
Opened in 1962, the Forest Service Visitor Center at Mendenhall Glacier was the very first in the United States. “When this visitor center was built, there were 23,000 visitors per year, and now there’s over 700,000,” James King, a region director for the US Forest Service in Alaska, told the Juneau Empire.
Current facilities are designed for up to 485,000 visitors per year. The growth in tourists has caused congestion, long waits, and an experience that is less than ideal for visitors to the 6,000 acre Mendenhall Glacier Recreation Area.
Robin Bouse, a tourist who visited Mendenhall last month, described the overcrowdedness. “The visitor center was crowded, so crowded that I couldn’t wait to get out of there,” she told GlacierHub. “I came from a cruise ship with about 4,000 passengers aboard and there were four similar ships in port that day.”
At its current capacity, the visitor center can only accommodate 4,000 people at a time.
In addition, tourist infrastructure will need to evolve to keep up with climate change. From satellite measurements taken by NASA’s Landsat 5 satellite in 1984 and Landsat 8 in 2013, Mendenhall retreated almost 4,000 feet, or three-quarters of a mile in under 20 years. Mendenhall Lake, which sits right at the terminus, has grown by roughly the same amount.
Another visitor to the glacier, Tim Denham, thought a visual representation of the glacier’s retreat over time would have been a valuable visual to add to the experience. “I think it would have been good to have big 4×4 posts with the years carved into them to show how rapidly it has receded,” he said.
By 2050, the glacier itself will no longer be visible from the huge windows that look out from the Mendenhall Glacier Visitor Center. ”The glacier ice was so beautiful and I felt fortunate to see it,” Bouse said. “It was easy to see that the glacier is retreating from the bare rocks surrounding it.”
From 2016 to 2018, six public meetings were held to develop a plan for revamping the Mendenhall Glacier Recreation Area and Visitor Center. The updated 50-year plan, published by the US Forest Service in February 2019 emphasizes major renovations over the next 10 years.
The Mendenhall Glacier Master Plan aims to create a sustainable recreation experience that can adjust to variations in glacier features. King from the US Forest Service estimated the project’s price tag at around $80 million.
As the glacier continues to retreat, the current viewpoints will become more strained, and visitors with a time limit––such as those who must return to their cruise ships––could subsequently be unable to attain the full experience.
“It was difficult to get up close to the glacier with the few hours I had to spend there, but the distant view was still spectacular enough,” said Bouse.
Denham similarly noticed the marked appearance of the glacier’s retreat, noting it was “barely visible across the lake. We hiked out a half mile on the trail but we were still too far away to see much.”
To accommodate increased glacial melt, the new plan proposes to switch from a land-based focus on hiking trails and viewing areas to a more water-based approach, complete with a commercial boat service to take people in small groups right to the terminus of Mendenhall Glacier.
There will also be a smaller mobile visitor center closer to the glacier itself. These new features will fulfill the frequently cited desire of tourists to truly be interactive with the glacier, allowing visitors to “touch the ice.”
Other parts of the proposed plan include more restrooms, a larger theater, and expanding parking availability. New walking trails will increase access to ecosystems newly exposed by the glacier’s retreat, including salmon, bears, and other wildlife. Finally, an additional visitor center will provide amenities such as food, restrooms, and directions, leaving the original building as an educational center and museum.
Taken together, these alterations could give the visitors a more pleasant and informative stay, showing them the glacier as it is now and as it had been. And it could awaken in them a sense of the urgency of climate change as a pressing issue, whether on vacation or back at home.
Mendenhall Glacier, near Alaska’s capital city of Juneau, is one of the most visited and oft-photographed glaciers in the United States. Kevin Lyons, an Alaska-based adventurer, uses his lens to offer a fresh angle on Mendenhall. Lyons is a self-described “photography enthusiast with a passion for travel and the outdoors.”
Dirt and cryoconite deposits on the ice surface inhibit the glacier’s ability to reflect solar radiation. Melt pools form on the ice surface, accelerating ablation by creating pores that allow water to penetrate the glacier.
Mendenhall’s retreat is well-documented, partly thanks to time lapse imagery provided by scientific cameras, like the one pictured below. The 2012 film, Chasing Ice, highlighted Mendenhall’s retreat to effect of global warming on the planet’s glaciers.
Mendenhall’s famous ice caves, pictured below, have collapsed since Lyons visited in 2014. A Frequently Asked Question on the U.S. Forest Service website addresses the rumor that ice caves exist at Mendenhall: “There have been several ice caves in past years, but the cave that appears in many recent internet photos has collapsed and disappeared. It was located along the west flank of the glacier but the ice has completely melted out of that area and no other caves are present.”
An indirect benefit for visitors and residents of Juneau is Lake Mendenhall, which did not exist prior to 1930. The lake formed due to excessive melt. The tongue of the glacier is expected to retreat to the point where it no longer terminates in the lake itself. According to Lyons, when the ice surface freezes just right “the hockey games out there are epic.”
Do you need to cool off from the stifling August heat?
Video of the Week is just what you need! This week we explore the melting ice caves of Alaska’s Mendenhall Glacier. Currently about 13 miles long, Mendenhall Glacier has been retreating for hundreds of years, and its melt rate has increased in modern times due to climate change. This melting, paired with failing ice dams, has put Juneau residents at risk for flooding as Mendenhall Lake’s water levels continue to rise.
This has not stopped thousands of people from visiting the glacier every year, however. The Mendenhall glacier is a popular tourist destination that flows from the Juneau Icefield all the way to Mendenhall Lake. In fact, the tourist-accessible features of the glacier are in the planning stages of being redone to incorporate new facilities and trails. Unfortunately, the ice caves featured in the video are not as easily accessible to visitors who want to make the adventure themselves. Mendenhall Glacier’s ice caves typically form and melt away quickly, so this video might have to suffice for now to help you escape this summer’s temperatures.
To learn about how Mendenhall Glacier helps teach about climate change, check out one of our articles from earlier this year.