Arctic landscapes and associated environmental concerns

Environmental geology course lecture outline

Content:


Introduction

Why consider arctic landscapes in this course? Fewer people live in high latitudes and high altitudes because it is cold. This factor reduces the overall risk. However, for several reasons we will still explore the environmental geology of these cold climate regions a bit in this introductory course. First, people do live there, and it is a distinctive and interesting environment with its particular set of environmental concerns. Also, climate change is most evident in this part of the world and so the landscape system is in disequilibrium. While fewer people live there, more change is occurring, introducing more uncertainty. Finally, it is clear that in the future more people will live there. Those at all familiar with the Ice Age also know that these conditions and processes used to exist over a much wider area, including here in Omaha. The landscape and geology of many places that are no longer cold was shaped by these processes, and hence, present day geologic resources and environmental concerns can be shaped by that Ice Age Legacy. Finally, in some ways the Arctic and other cold climates are a remaining frontier, and one can predict that more and more human activity will migrate into these areas. One of the most distinctive aspects of these environments is permafrost, and so we will delve into this topic a bit more first.

This polished and striated bedrock surface in Omaha was produced by glaciers from one of the earlier phases of the Ice Age (more technically known as the Pleistocene). A continental ice sheet extended all the way down into Kansas from the interior of Canada. As the glacier moved over the bedrock (in this case an orange sandstone known as the Dakota Sandstone) it was carrying rock debris, which scoured, polished and striated the surface leaving these very distinctive features. The ice movement was basically to the south, as would be expected.

This is a somewhat generalized map showing the extent of the Pleistocene Ice Sheet. That such an entity existed only some 15,000 years ago (recent geologically) shows the extent of change that can occur. The ice sheet was far from static, but shrank and grew significantly. The most recent advance of the ice sheet only reached down to Madison, Wisconsin and to the northeast border of Nebraska, but earlier advances dipped down into Kansas. Map taken from USGS publication - Our Changing Continent by John Schlee - https://pubs.usgs.gov/gip/continents/ .


What is permafrost?

Permafrost is ground that is permanently frozen due to the cold climate, and therefore occurs at high altitudes and high latitudes. Permafrost strongly influences the biologic and geologic character of the landscape. It can be anywhere from several meters to hundreds of meters thick.

Map from USGS showing permafrost distribution in Alaska. As one would expect latitude is a primary control on permafrost distribution because it strongly influences temperatures. Source: http://pubs.usgs.gov/ha/ha730/ch_n/N-AKtext1.html

On a walk through the tundra biome in Alaska. The tundra here is underlain by permafrost. Note the relatively small trees. What is limiting their growth? Much tundra is treeless. The board walk is used because much tundra is boggy in the summer as the upper portion of the permafrost melts to form what is known as the active layer. Some of these small trees can be quite old. As you can imagine growth in these cold areas can be quite slow. Scars of disturbance on tundra can persist for at least many decades,

Active layer: this is the upper layer of permafrost that goes through seasonal freeze-thaw cycles, and as a consequence is very mobile. It can sort and shape the sediment into distinctive geometric patterns - stone and ice polygons, stone circles, stone stripes. This phenomena is known as patterned ground.

Photo of patterned ground from Midterhuken peninsula, Spitsbergen, Norway. These patterns are due to the constant freeze thaw cycles off the upper active layer in permafrost regions, which puts the soil in motion. Note the hexagonal pattern. Where else in nature do you see this pattern? It is the mobile, dynamic nature of these permafrost surface layers that produces a lot of engineering concerns.

Patterned ground on Mars. These patterns are polygenetic and there might not be a lot of thaw going on at present on Mars (it is fairly cold), or there is another possibility we have not thought of yet. Image NASA/JPL/Malin Space Science Systems, http://photojournal.jpl.nasa.gov/catalog/PIA05951

Photo of a section of the Alaska pipeline. Why isn't it buried like most pipelines? There are two major concerns that influenced the pipeline design, permafrost and earthquakes. The oil in the pipeline is heated to make it flow easier. If it was in the ground what would happen? Note the device with radiating fins on top of posts holding up the pipeline. Also note the small trees - typical of areas with permafrost. This is just one of the many ways that permafrost presents an engineering challenge.

Thermokarst: these are melt pockets that develop in the permafrost. Why would some areas thaw more or thaw less? How they absorb versus reflect sunlight is of course a key consideration. When they are frozen the lakes will likely reflect more than the surrounding ground (depending on the amount of snow cover), while once they are thawed, they can absorb more. They get more solar radiation in the summer and less in the winter. There may be a delicate tipping pont where on an average yearly basis they start soaking up more solar radiation than the surrounding tundra. This can cause the banks to melt more, collapse, and the lake to grow larger.

Abundant lakes in permafrost regions of Siberia.Note the very different colors of the various lakes. What feedback loop might enlargen these lakes with time? Image source: NASA Visible Earth - http://visibleearth.nasa.gov/view_rec.php?id=17371

Image showing how thermal 'coupling' of surface features and permafrost is important. When lakes are darker, they can absorb more sunlight, which in turn melts more of the permafrost. Source: USGS http://pubs.usgs.gov/ha/ha730/ch_n/N-AKtext1.html

Aerial image showing development of new ponds in an area of polygonal ice wedges from the Alaskan Arctic Coastal Plain. The pattern of ponds is influenced by but superimposed on the polygonal pattern, providing insight into the history of change. Image source - USGS site on Arctic Coastal Plain Studies - Chipp River Studies (retrieved 10/10/2017) - https://alaska.usgs.gov/science/wild/abc/acp.php .

As you might guess the mobility of the active layer and the present rate of change in these colder regions produces many more engineering challenges. If you have driven on the Alaska highway you can see the effects. A USGS summary can be found here - Permafrost and related engineering challenges, pubs.usgs.gov/pp/0678/report.pdf .


What is the significance of permafrost as a methane reservoir?

The crucial fact here is that methane (CH4) is a greenhouse gas, and can contribute to global warming. This produces the potential for a positive feedback loop between warming and methane release. Methane has a much short residence time in the atmosphere because it is more reactive than CO2.

Methane leaking from below and captured in surface ice. Of course this will be shortly released to the atmosphere. Image source: USGS site on permafrost - http://www.usgs.gov/blogs/features/usgs_top_story/permafrost-its-chill/ .

There are many lines of evidence that permafrost is degrading (melting) at an accelerated rate. The above graph is only one small bit of it. Image source: http://geochange.er.usgs.gov/poster/permafrost.html .

The graph above this one shows the data for one site. What is the larger picture? The graph shows summary data from multiple sites from around the world. The x axis is, of course, time in years. This data suggests that permafrost temperatures are increasing with time on a much broader scale. There is also some interesting variation between and within site data. This data is consistent with the idea of a changing landscape in process disequilibria. Graph from Williams & Ferrigno, 2012, State of the Earth’s Cryosphere at the Beginning of the 21st Century: Glaciers, Global Snow Cover, Floating Ice, and Permafrost and Periglacial Environments, USGS Professional Paper 1386 (retrieved 10/10/2017)-Ahttps://pubs.usgs.gov/pp/p1386a/gallery5-fig09.html .


Accelerated coastal erosion of permafrost areas

It is very clear that certain Arctic shorelines have begun to retreat at much faster rates than historically observed. Coastal villages are being moved because of this. Why has erosion greatly accelerated (one hint - how might it be related to reduced sea ice)?

Photo from USGS website - http://soundwaves.usgs.gov/2009/05/research2.html - showing an area of accelerated coastal erosion. The undercutting that is occurring is more obvious here. Note how the water is also relatively ice free. This provides a greater area for the wind to blow over, resulting in larger waves, which play such a significant role in shoreline erosion.

Example of how the changes can be mapped through time. This one shows significant shoreline erosion. Image source: http://energy.usgs.gov/alaska/ak_coastalerosion_images.html

 


Glaciers

UNO students on the Matanuska glacier in Alaska. This is the front part of the glacier where melting dominates, which has created the rough topography on the glacier. Note all the rock debris the glacier is carrying, and which is being concentrated on the surface of the glacier as the ice melts.

What is a glacier?

Environmental significance of glaciers?

Trees being plowed under by an advancing glacier. Source of photo: http://nsidc.org/glaciers/gallery/piedmont_marginNV.html
NSIDC/WDC for Glaciology, Boulder, compiler. 2002, updated 2005. Online glacier photograph database. Boulder, CO: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media


Jokulhaups (how do you say that)?

This is an Icelandic word for very large floods that occur there periodically. They are associated with glacial lakes with unstable ice dams.

Picture of Hubbard glacier after it has surged up in Alaska. Image source: USGS

Breakout flood past the ice dam. Image source: Photo by US Forest Service Yakutat Ranger District, June 20, 2002, during the current near Russell Fiord closure. USGS website: http://ak.water.usgs.gov/glaciology/hubbard/

First identify the various features in this landscape. Can you detect the elements that allow for a small breakout flood to occur?

This is a close up of the lake at present. Where would you drill or sample to get a record of lakes building up and then draining?

Channeled scabland story. Channeled scablands are a very distinctive landscape in Washington State now understood to be created by very large (very, very large) jokulhaups.

Photo of only a portion of Dry Falls, part of the channeled scablands in central Washington State. The lakes are the plunge pools from when this entire view plus more was a gigantic series of waterfalls. The small white specks in the distance are a town, and give some idea of scale.

This is downstream from Dry Falls and the large basalt boulders just behind the car were carried along by the jokulhaup currents, and the depth of the water exceeded the height of the cliffs in the background.

A map from the visitor's center at Dry Falls showing the ice sheet, the position of the large glacial lakes associated with the Ice Age, the location of the crucial ice dam, and the path that the floods covered.

Plague commemorating the geologist who initially figured out this story, Harlen Bretz. His ideas were not initially well received, but with perseverance the geologic community came to see he was right.


Role of glaciers in global climate change: