Update on glacier recession

 

 Oh, how I miss Quelccaya! It has been three years since we've been able to do fieldwork at Quelccaya Ice Cap, a result of removing the AWS and the COVID-19 pandemic. Nonetheless, satellite imagery provides a glimpse at changes continuing at the glacier.

The image pair above illustrates one portion of the ice cap margin as it appeared last week (upper), and just prior to our last visit, in 2018 (lower). The red dots are co-registered to provide a perspective on examples of change over the three years. As in the past, ice recession has not been uniform along the margin. Retreat is especially dramatic at the formerly proglacial lake Morojanicocha. Collaborator Gustavo Valdivia visited this area in September, was able to walk entirely around the lake, remarking that it is "incredible how fast the ice is retreating".

Also note the change in waterlevel at the lake at the top of both images. The obvious drop may reflect seasonal lowering during the June - September dry season, but may also be a response to longer-term hydrological changes associated with ice retreat.

Other environmental changes at Quelccaya are less easy to interpret from imagery at this resolution, such as the magnitude of glacier thinning. Also, changes in the volume and routing of meltwater runoff from the glacier over time are difficult to assess from imagery, due to the combination of seasonal and diurnal variability, as well as the five-day image acquisition interval.

The landscape around the ice cap supports tremendous biodiversity, due largely to meltwater storage in down-valley lakes and wetlands (bofedales). As the volume of runoff decreases, the many species dependent upon the water are needing to adapt or relocate.

Another change with biotic effects is the glacier-surface morphology, which we have observed over the past two decades. Quelccaya is where breeding by the world's only glacier-nesting bird species has been observed, as described here, here, and here. These Glacier Finch (Idiopsar speculifer, formerly known as White-winged Diuca Finch, Diuca speculifera) will only build nests in crevasses and very steep, fissured margins - both of which tend to disappear as the glacier has thinned and retreated.

We remain optimistic about returning in the next few years to this amazing place, to document and measure changes since our last visit!

Recession continues

 

These two Sentinel-2 images show changes over 4.5 years at a portion of Quelccaya's western margin. The view includes Lonnie Thompson's Base Camp (lower left) for fieldwork since the 1970s, and the marginal lake we refer to as Morojanicocha.

Some visible differences are seasonal, such as the higher water levels in May and lower-albedo ice in the ablation zone during November (also with less snowcover).

Most notable is ongoing retreat of the ice margin, particularly towards the bottom of the image where the ice is thinner. Ice is no longer calving into the lake, and our colleague Gustavo Valdivia reports that it is now possible to walk entirely around it on rock.

The importance of fieldwork

White-fronted Ground Tyrant (Muscisaxicola albifrons) with crane fly larvae and adults

Since first visiting Quelccaya in 2003, the objective of our work has been to accurately establish the summit climate, and quantitatively document how climate is recorded by the glacier - illuminating what we can learn about climate from ice cores. These efforts are documented in publications, with more still in preparation.

Working at high elevation on the glacier requires a bit of physical exertion (e.g., digging snowpits, wrestling with AWS tower extensions), as well as mental concentration (e.g., electrical wiring, datalogger programming). In spite of these requirements - or perhaps due to them - we also spend time at Quelccaya simply making observations, of both abiotic and biotic features and processes. These 'distractions' were often fascinating, including ice caves, streamflow and sediment transport, atmospheric convection, and abundant wildlife.

Our avian observations revealed behaviors previously unknown, some of which we have published (see here, here, and here), while others remain only partially understood. Another observation remained only in notes and photographs until recently, involving a fly. Since 2004, we encountered a large fly species at the AWS, typically clustered beneath the snow surface in proximity to the tower tubing and buried instrument enclosures. During transition-season visits in April and October 2014, we observed the flies on the snow surface at our moraine camp (5,200 m), crawling around in our tents, and being eaten by birds.

We posted photographs of this fly species on iNaturalist, where it remained unidentified for five years. In November, Russian entomologist Dmitry Gavryushin observed the report and took interest. He was able to identify the crane fly to species, based on a speciman from Bolivia described by prominent crane fly taxonomist Charles P. Alexander, who was affiliated with the UMass Entomology Department from 1922-1959. The coincidences continue, for the type locality for Dicranomyia (Dicranomyia) perexcelsior (Alexander) is Chacaltaya Glacier in the Cordillera Real of Bolivia. This is where Niethammer (1953) first described an association between Andean glaciers and our "Glacier Bird" (White-winged Diuca Finch; Idiopsar speculifera).

Our Quelccaya crane flies are the highest-elevation observations from anywhere in the world, which came to the attention of Pjotr Oosterbroek at the Naturalis Biodiversity Center in The Netherlands. Pjotr's enthusiasm and initiative drew in Christophe Dufour from the Muséum d’histoire naturelle in Neuchâtel, Switzerland, and resulted in our latest publication, on high-elevation crane flies. Working with these two was an absolute pleasure.

Our experience at Quelccaya demonstrates that casual observations from seldom-visited, extreme environments are often invaluable. When making them outside of one's field of expertise, one can never know just how important they might be. This is especially true during the rapid environmental changes underway. Chacaltaya Glacier, for example, no longer exists; no one will ever again observe crane flies or Glacier Birds there. Sadly, this will likely also be the case at Quelccaya before the end of the century (Yarleque et al., 2018).

 

Update (with Cranefly news)

Our AWS on Quelccaya has been decommissioned, and everything except deeply-buried tower tubing has been removed. Meteorological measurements spanning 2003 to 2018 are currently being analyzed; we welcome collaboration and data-sharing inquiries.

At least one aspect of our glacier field research will continue for another year. Also, we aspire to investigate the impact of continuing glacier recession on avian activity at Quelccaya (as reported here and here).

This week we learned more about a particular insect that was typically found at the AWS each time we visited for service and data recovery. Individuals and clusters of craneflies were observed beneath the snow surface in association with the AWS tower tubes (see above and below photos). We also observed craneflies on the snow surface near the AWS, elsewhere on the glacier, and at our glacier-margin camp. Craneflies appear to be an important food source for the many high-elevation bird species in the Quelccaya area (> 5,000m).

Cranefly photos were posted to iNaturalist after fieldwork in April 2014, seeking identification. These were identified this summer - after 6 years - based on a single specimen from Chacaltaya in Bolivia. Interestingly, this is the same location where the "Glacier Bird" (White-winged Diuca Finch, Idiopsar speculifera) was first observed in association with glaciers; Chacaltaya no longer exists.

The Quelccaya cranefly species is Dicranomyia hirsutissima. According to Pjotr Oosterbroek, author of "Catalogue of the Craneflies of the World", this is the highest known Cranefly record for all 15,000+ species found throughout the world.

This is yet another fascinating discovery from Quelccaya and the Cordillera Vilcanota, during nearly 50 years of investigation begun by Ohio State University scientists John Mercer and Lonnie Thompson.

Quelccaya Images

A new index (of sorts) has been compiled to better organize Quelccaya images depicting the weather station, snowpit measurements and sampling, as well as other aspects of fieldwork:  Quelccaya Gallery.

Links to images of birds living and nesting around & on the glacier are here.

New paper: birds & glaciers at Quelccaya

Important scientific information has been emerging from research at Quelccaya Ice Cap for nearly 50 years, from ice core records, glacial geology studies, and meteorological measurements. In recent years, research has also yielded new biological findings, revealing the importance of glaciers to the lives of birds in the High Andes.

We published a paper in 2008 documenting nesting on glacier ice at Quelccaya by White-winged Diuca-Finches. Diucas are a medium-size tanager species found in the High Andes of Peru, Bolivia, and Chile, and prior to our new publication were the only bird known to routinely build nests directly on glacier ice. This species is also among the highest-elevation nesting species in the world – to at least 5400 meters (18,000 feet) – despite an environment with average temperatures below freezing, high winds, frequent snowfall, and intense solar radiation.

Our paper in the latest Wilson Journal of Ornithology provides new details on this unique behavior. Ten years of additional observations include fieldwork at Quelccaya outside the core dry season, culminating in 2 weeks at the glacier in 2016 filming a Diuca nest with 2 chicks. Besides observations of multiple active nests, the paper also documents glacier nesting by another species, the White-fronted Ground-Tyrant, and describes nocturnal roosting within or under a glacier by 5 different species. The publication includes an online Supplement (also available here) containing additional images, and links to the BBC/PBS film.

Nesting and roosting on glaciers are adaptations to the harsh environment at high elevations in the Andes, as cavities within the ice provide both a protected microclimate and protection from predators. Are glaciers important to other species, elsewhere? What happens when the glaciers are gone, victims of climate change?

Andean glaciers are shrinking rapidly, and even the largest are likely to disappear this century. Although undocumented until only 10 years ago, the lives of several bird species appear to be dependent upon these glaciers. Their loss may have a direct, negative effect on biodiversity of the High Andes - in addition to other impacts, such as water resources.

Seasonal change

The second half of September at Quelccaya is typically characterized by increasing snowfall, as the dry season concludes. Cloudiness increases rapidly at this time of year, as evidenced and measured by sharply increasing longwave radiation receipt. Air temperature continues a steady increase into November.

These aspects of Quelccaya climate are illustrated by the 2 images below, acquired by Senitinel-2 only 5 days apart. On 27 September (upper image), fresh snow is evident at higher elevations of the Vilcanota, particularly on glaciers and eastern portions of this scene. By 2 October (through high thin clouds), fresh snow had ablated from the landscape (middle image). Lower elevations of Quelccaya Ice Cap also become snow-free, revealing the transient snowline (also see lower image).

Further evidence of this seasonal change in climate is provided by the lower image - an enlargement of yesterday's image - showing the apparent disappearance of ice cover from a marginal lake (circled). In July this ice was thick enough to support a person walking across the lake.

 

Return from fieldwork, forthcoming papers [updated]

August fieldwork was successful and fun, despite rather unstable weather. Considerable dry-season snow blanketed south-facing slopes and the entire glacier, yet little new snow occurred during our ~10 days at Quelccaya. The panorama above shows Boulder Lake and one lobe of the glacier where we have conducted observations since 2003; Lonnie Thompson has worked here since 1974. More photos and details of recent fieldwork will be posted in the next week or two.

A variety of new papers will soon be available, so look for links on this website. As indicated below, some are closer to publication than others...

[UPDATE 10/16] Yarleque, C., M. Vuille, D.R. Hardy, O.E. Timm, J. De la Cruz, H. Ramos, and A. Rabatel. Projections of the future disappearance of the Quelccaya Ice Cap in the Central Andes. 2018. Scientific Reports. To be freely available on 22 October from Nature!

Hardy, S.P., D.R. Hardy, and K. Castañeda Gil. Avian nesting and roosting on glaciers at high elevation, Cordillera Vilcanota, Peru. Accepted 20 Aug. for Wilson Journal of Ornithology.

Hurley, J.V., M. Vuille, and D.R. Hardy. On the interpretation of the ENSO signal embedded in the stable isotopic composition of Quelccaya Ice Cap, Peru. Submitted to JGR-Atmospheres.

Yarleque, C., M. Vuille, D.R. Hardy, O.E. Timm, and H. Ramos, Future projections of precipitation variability over the eastern Central Andes. Submitted to Frontiers.

Chadwell, C.D., D.R. Hardy, C. Braun, and H.H. Brecher. Thinning of the Quelccaya Ice Cap over the last thirty years. In revision/reorganization.

Hardy, D.R., R.S. Bradley, et al. The summit climate of Quelccaya Ice Cap. In preparation.

More snow this week

As forecast by SENAMHI, the Vilcanota has received more snow. The Sentinel-2 image from yesterday shows snowcover surrounding Sibinacocha, as well as the area around the hamlet of Phinaya.

weather forecast: more of the same

The weather forecast for today and tomorrow from SENAMHI calls for rain and snow of moderate to strong intensity in the mountains, with hail expected above 3,000 m; wind gusts to 45 km/hr.

Quelccaya's location here is indicated by the red circle. "Danger Level 3"

And it appears the forecast was accurate, with restricted travel...

#TVPerúInforma

August begins snowy

Sentinel-2 acquired an image of the Cordillera Vilcanota yesterday, 11 days since their previously-published image (via EO Browser)... and fresh snowcover is still widespread.

Compare these two identical scenes, from 3 August (upper) and the last time snowcover was restricted to the highest elevations, on 30 May (lower) - two months ago!

The community of Phinaya, where many alpaca and llama herders are based, is located within the red circle. During June and July, snowcover appears to have been only occasional at this elevation. The smaller red hexagon is the Quelccaya weather station location (5,680 m), illustrating that the transient snowline has remained below the glacier margin (approx. 5,300 m) since May.

Fieldwork begins in a week!

¡Tanta nieve! So much snow! [updated x2]

The snowy dry season of 2018 continues in the Cordillera Vilcanota. Yesterday's Sentinel-2 image (above) reveals a landscape blanketed by snow above 4500-4700 m. Quelccaya Ice Cap (lower right) is difficult to delineate, suggesting substantial accumulation at the margin. Hopefully our instrumentation continues to record hourly snowfall at the summit.

Note the variation in color of lakes just west of the glacier, surrounding the area of our camp (labeled). This reflects varying suspended sediment input, with relatively high concentrations apparently flowing into the Qori Kalis proglacial lake (north of camp); snow is accumulating, while also melting and delivering sediment to the lakes. The 'double' lake to the northwest of camp (and Sibinacocha) appear dark blue, as upstream wetlands (bofedales) filter sediment from freshly-exposed areas proximal to the glaciers.

We will be in the area during the second half of August, measuring snow and recovering weather station data. Fieldwork will occur later than normal, allowing an assessment of what appears to be an anomalous year. Although this snow will be beneficial to glacier mass balance, the toll on camelids (llama, alpaca) could be severe - without warming solar radiation typical of the dry season.

[UPDATE 7/26: A press release from SENAMHI* earlier this week (23 July) describes snowfall in the preceding 72 hours above 3,800 m in the Andes, accumulating to 20 cm. In conjunction with clouds, they warn of low temperatures and prolonged snowcover reducing food for livestock.

Gustavo Valdivia wrote yesterday learning details of the situation in the Cordillera Vilcanota. He received a call from the Phinaya community president, who described the situation as critical, because a lot of alpacas died in recent days. The local people agree that the weather is very unusual.

Press releases from SENAMHI can be found here (in Spanish), with a machine translation  here. 

*SENAMHI is The National Meteorology and Hydrology Service of Peru or El Servicio Nacional de Meteorología e Hidrología del Perú]

[UPDATE 7/27:  Today I learned from Bronwen Konecky (Washington University) that SENAMHI is making daily meteorological summaries available on their website. The closest station to Quelccaya - and one of their highest - is Sibinacocha, at ~4890 m (labeled on map above). These data show 11 mm of water equivalent precipitation on 21 July, followed by 5.9 on the 22nd. Since this automated station is located at the southern end of the lake, the image above suggests that considerably more snow fell at higher elevations. The regional nature of this event is demonstrated by daily totals from Sicuani (~3600 m, 45 km to the SW); very similar daily totals were recorded.

To access any SENAMHI data in Peru, go here, then use the "Seleccionar" button to select a District; zoom in on the map. Thanks, SENAMHI.]

BBC Glacier Bird filming

During our April/May 2016 fieldwork, we were joined by a BBC Natural History Unit crew. Their objective was to film White-winged Diuca Finches nesting on the glacier, a breeding behavior unknown among all other bird species. The project timing was fraught with uncertainty, for only 2 other active Diuca nests had ever been observed, and the 2015-16 El Niño event considerably impacted Quelccaya climate (overview here of a manuscript now out for review). Foremost in our minds was whether we could find active nests to film, when we arrived in April.

Fortunately, our timing was perfect; we observed all stages of breeding behavior, and successfully installed a remote camera at one of the nest sites. After a year in production the segment aired on BBC as part of an episode on the Andes, in the series Mountain: Life at the Extreme. Links to the BBC series are here and here.

This month, BBC Glacier Bird footage will premiere in the United States on PBS. The series takes a new name, Kingdoms of the Sky, with a new presenter, but otherwise appears identical: a three-part documentary "revealing the extraordinary animals and remarkable people who make a home on the iconic mountain ranges of the world - Rockies, Himalaya and Andes." The three episodes will initially air on Wednesday evenings, beginning with The Rockies on July 11 at 9 PM EDT. Himalaya premieres one week later on July 18, and Andes premieres on July 25.

The PBS series website is here, and DVDs can be pre-ordered now.

At the moment, the Glacier Bird segment can be viewed from the right-hand side of the series homepage. Click on "Meet the Bird that Nests Inside Glaciers" to see the first-ever footage of Diuca speculifera nestlings.

Even better is an 8-minute, behind-the-scenes look at Quelccaya filming, available from PBS here. Images from that clip are included above and below.

Our extended fieldwork with BBC in April 2016 was good fun, and provided new observations of Diuca and other high-elevation species. Please check our website for the Glacier Bird, and stay tuned for a new publication (still in review; contact us for a synopsis of the paper, or a pre-print).

Still Snowy - Quelccaya and beyond

The Cordillera Vilcanota remains snowy, as illustrated by the Sentinel-2 image above from 4 July. Snowcover at high elevations, on south-facing slopes, and on glaciers has changed very little over the past month. At Quelccaya Ice Cap, bare ice is exposed only at the lowest elevations of outlet glaciers (e.g., Qori Kalis, on west side).

Extensive snowcover on the glacier is keeping the albedo high, minimizing mass loss... at least for the moment.

Quelccaya is not alone in being unseasonally snowy this year. For example, in the Karakoram Mountains (Pakistan) climbing teams on mountains such as K2 are finding dangerous avalanche conditions due to heavy snowfall, during the core climbing season. More details can be found here.

Kilimanjaro is also unusually snowy for July, the result of above-average accumulation during the March-May wet season.

In Northeast Greenland, the winter of 2018 brought twice as much snow as the long-term average, and snowcover into early July remains so extensive that Sanderlings and other shorebirds may not even attempt nesting this year. The late snow is having large consequences for the ecosystem.

Finally, snow on portions of the Greenland Ice Sheet is resulting in the "least surface ice loss in decades". As Jason Box notes via Twitter (@climate_ice), these persistent extremes in patterns of atmospheric circulation are an expected signature of climate change.

June snow

Several snowfall events during the first half of June have kept the landscape snowy at Quelccaya this year. In the 14 June image above (ESA Sentinel-2, bands 4,3,2) lingering snow is visible below 4,900 m in shaded locations.

Typically the dry season is underway by mid-June, often with snow only on the glacier. This year, the relatively-bright fresh snow is keeping the albedo low, reducing energy input and ablation of the glacier surface.

Despite the current situation, evidence indicates that recession of the ice margin is accelerating. Planning is underway for fieldwork in the next few months, when snowcover on the glacier will be measured and AWS data since July 2017 will be recovered. We're anxious to document 2017-18 La Niña accumulation!

Snowcover update & ice retreat

Quelccaya Ice Cap currently remains largely blanketed by snowcover, excepting the very lowest ablation zone (e.g., Qori Kalis outlet glacier). The GIF above contains only 2 images; the snowy scene without red annotation was acquired last week (10 May 2018). Contrast 2018 snowcover on the glacier with that 2 years earlier, at the end of March 2016.

These images show a portion of the ice cap's western margin. We have visited this area at least annually since 2003, witnessing continuous retreat of the margin and changes in all of these proglacial lakes.

The red ellipses on the 2016 image highlight two areas where margin retreat is clearly evident. Our GPS measurements up through 2017 at the lower section indicate a retreat rate of 10-15 m/year. At the small red circle by the larger lake, the area of bedrock near the circle has expanded, and only a small portion of the glacier still extends into the lake (contrast 2013). Throughout our years of fieldwork in the area we have observed ice calving into this lake, which began forming in ~1985 (Thompson et al., 2013). Within the next year or two the glacier will no longer reach the lake.

One consequence of Quelccaya margin retreat and thinning is loss of suitable nest sites for the "Andean Glacier Bird" (White-winged Diuca-Finch, Idiopsar speculifer; formerly Diuca speculifera). Until the mid-2000s the area near the lower ellipse supported a relatively high density of nests, built directly on the ice (Hardy and Hardy, 2008 and here). As ice at this margin thinned and became less steep, the area was abandoned for nesting. More recently, the area near the small circle has been used for nesting (e.g., 2014 oblique photo of margin at the lake), but as the ice becomes thinner the birds will need to move up in elevation to find suitable, steep ice slopes. Furthermore, the Glacier Bird is not the only bird species impacted by ice recession; a new manuscript detailing this is currently in review (and available upon request). 

Ref:  Thompson, L.G., E. Mosley-Thompson, M.E. Davis, V.S. Zagorodnov, I.M. Howat, V.N. Mikhalenko, and P.-N. Lin. 2013. Annually resolved ice core records of tropical climate variability over the past ~1800 years. Science, vol. 340, 945-950. 10.1126/science.1234210

Vilcanota wet season

Image above:  A portion of the Cordillera Vilcanota, including Nevado Ausangate (upper left), Sibinacocha (the big lake), and Quelccaya Ice Cap on 31 March 2018 (Sentinel-2 image).

Our ~15 years of measurements reveal clear relationships between ENSO and climate at Quelccaya. A detailed documentation of these is nearly ready for submission, primarily authored by collaborator John Hurley and titled "ENSO variability of Quelccaya Ice Cap d¹⁸O”

Our understanding of Quelccaya's response to ENSO will be further refined when we are able to examine accumulation resulting from the ongoing La Niña event (2017-18). Since last September, negative sea surface temperature anomalies have persisted in the east-central equatorial Pacific. These SST anomalies have been slightly more negative than last year, which followed very warm anomalies associated with the 2015-16 El Niño.

Quantifying the timing and properties of this newest accumulation cannot occur until we visit the weather station, since our data telemetry system failed in 2017. However, satellite imagery suggests that snowfall has been considerable this year. The image above provides the first relatively-clear view of the glacier and surrounding terrain in several months. In this ESA Sentinel-2 "natural-color" image (bands 4, 3, and 2), glaciers and higher peaks are entirely snow covered, and a dusting of snow is visible on terrain west and south of Quelccaya.

Greater detail can be seen in the cropped image below, showing only Quelccaya - and revealing that glacier ice is not exposed even at the lowest elevations (~5,200 m).

Finally, the GIF image at the bottom shows the Sentinel-2 EO Agriculture composite product, on approximately 1 April of the past 3 years. Note in particular the vegetation color difference between the El Niño year 2016, and the next two wet seasons during cold phase ENSO events. Also, there appears to be more snow around the glacier margin this year than in April of 2017. Our ENSO paper will document such ENSO variabilty at the summit of Quelccaya, in terms of snowfall seasonality, the vapor initial d¹⁸O values, and air temperature.

2017 dry season - towards the end

Satellite imagery from earlier this month show that the 2017-2018 accumulation season began sometime within the past month. The image above from 2 October shows a familiar snowline pattern, as ablation continued. We won't know exactly when accumulation began at the summit until our next visit to the AWS, as telemetry was not restored during July fieldwork. Will there be a La Niña signal in accumulation this year?

Glacier Bird on BBC

The final episode of BBC TWO's new documentary series about mountains will air at 9 pm on 13 September, featuring a variety of sequences filmed in the Andes.

Among the Andes sequences will be a segment filmed at Quelccaya, as described above. Several wonderful "behind the scenes" clips have been produced for the Glacier Bird film, one of which is here (hopefully available soon in North America). A link to the page above, with an embedded clip, is here.

Since the time of filming - just last year - science has moved forward:  we have discovered a second species of bird which also nests on the glacier (Hardy et al., submitted to Wilson Journal of Ornithology), and Glacier Bird's taxonomic classification has changed from Diuca speculifera to Idiopsar speculifer. The common name in English remains White-winged Diuca-Finch, but this too may change because the bird is not a Diuca-Finch!

For those not in the UK, the series will be broadcast in North America by PBS at a later date.

"Mountain: Life At The Extreme" (new BBC series)

On Wednesday evenings at 9 pm starting 30 August, television network BBC TWO will be airing a new 3-part documentary series exploring three different mountain ranges: the Rockies, the Himalaya and the Andes.

Each episode is more than a natural history program in that it depicts examples of both the "extraordinary animals and remarkable people" living in these extreme environments (quote credit here).

The Rocky Mountain sequences feature wolverines, extreme skier Hilaree O'Neill, big horn sheep, and Native American horse racing - among others. Clips and more are available on their website:  <http://www.bbc.co.uk/programmes/b093x4gb>

The Himalaya episode also features animals, along with the people comprising remarkable ancient cultures. One exciting sequence follows Nepali ultrarunner Mira Rai through a race. (Mira is featured in the May 2017 issue of Outside Magazine, and will be running one of the UTMB races in Chamonix this week.) For more on the episode, including clips and updated information, check the BBC website: <http://www.bbc.co.uk/programmes/b094klt5>

Details on the final episode airing 13 September have not yet being released. This post will be updated when they are - for it includes a sequence on our work at Quelccaya.

Unfortunately for North Americans, BBC TWO is not available. There will be rebroadcasts by PBS, but dates are not yet available.