SEGH Articles

The evolving role of environmental geochemistry in Alaska

02 July 2018
Dr Keith Torrance, Principal Consultant at Environmental Resources Management in Alaska, provides us with a unique insight into the diverse field of Environmental Geochemistry in the state.

Alaska is the 49th state of the United States of America and is strategically situated between Canada and Russia; the only part of the United States that lies partly above the Arctic Circle.  The image of Alaska that is most frequently brought to mind is of pristine mountain peaks, snow-capped volcanoes, spectacular fjords, and glaciers, graced by moose, bear and caribou.  A magnificent wilderness that is untouched by the industrialization that has blighted other parts of the United States. While the reality is that Alaska is even more breathtaking than you can possibly have imagined, the state is still facing many environmental impacts related to climate change and development of natural resources that can benefit from a better understanding of how environmental geochemistry affects health.  Consequently, Alaska is home to an active group of geologists, geochemists, and environmental professionals who are collectively working to study the geochemistry of soils, ice and water within the state. This article is intended to give an overview of some of the areas that are of interest to SEGH members.

 

Flying over the glacier on Denali National Park


Geological Setting

The continental mass of Alaska has been built up through the accretion of different terranes producing a complex geology endowed with metallic mineral deposits (Au, Zn, Ag, Pb, Cu), extensive coal and oil and gas resources. It is an understatement to say that Alaska has some of the most interesting geology on the planet and is one of the best places to see geomorphological processes first hand. About 5% of the state is covered by glaciers, some of which are readily accessible from Anchorage. There are over 130 volcanoes in the state, forming the Aleutian Island chain. Together with the Aleutian Trench, this arc delineating the zone where the Pacific Plate is being subducted under the North American Plate. At any given time, at least one of these volcanoes along the 3,400 kilometer length is active, often explosively. Seismicity associated with this tectonic plate movement is responsible for frequent powerful earthquakes that shake Southcentral Alaska, including the Great 1964 Alaskan Earthquake, which had a magnitude of 9.2.  Tsunamis and landslides complete the suite of geohazards associated with Alaska’s tectonic setting.

Mercury

Subduction related volcanism is also a major influence on the geochemical signature of Alaska. As oceanic crust and sediments are subducted under the North American Plate, their high water content causes partial melting of the mantle and the formation of intrusive magmatic bodies. These are imparted with oceanic geochemical signatures that can produced enrichments of copper, arsenic, chromium and mercury which can lead to the formation of ore deposits. The flux of atmospheric mercury from these volcanoes is largely unstudied, but likely contributes to deposition rates during major eruptions. Mercury is a significant health concern in Alaska for several reasons. Firstly, gaseous elemental mercury is known to travel long distances from source before being sequestered in the Arctic.  Consequently, mercury emitted into the atmosphere during coal burning in Asia can be carried by prevailing winds as far as Alaska. A second factor is the prevalence of subsistence living in Western Alaska, where locally caught fish, such as salmon, pike and burbot, form a high percentage of the diet of rural villages. The State of Alaska has issued advisories to limit consumption of certain fish species by women who are pregnant or can become pregnant.

A more tangible expression of this mercury deposition are epithermal mercury deposits that formed in response to shallow depth volcanicity along a wide belt across the Kuskokwim River. Several mines in the region worked these deposits for mercury and gold, but the most notable is the Red Devil Mine, which operated from 1933 until 1971 producing around 1,224 tonnes of mercury. After mining ceased in 1971 the property was abandoned. Mine tailings with high concentrations of mercury, antimony and arsenic have been eroding into the Kuskokwim River and are a concern for local residents. The responsibility of cleanup has fallen to the Bureau of Land Management (BLM) which manages land on behalf of the Federal government.  The logistics of remediating a remote property such as Red Devil are challenging, with air and river transport the only options open for bringing in equipment and removing contaminated media.  Not surprisingly this greatly increases the cost of addressing environmental issues on this property to the satisfaction of local stakeholders.

Lucky Shot Mine

The abandoned Lucky Shot Gold Mine, Hatcher Pass, Alaska

 

A more imminent threat to rural communities on the western coast of Alaska is the consequences of climate change, which have been more extreme in the Arctic.  The most visible effect of rising temperatures is increased erosion rates along the coastline caused by longer ice-free periods. This is coupled to the susceptibility of permafrost to wave erosion and deeper seasonal melting, producing annual erosion rates in the tens of meters at some locations. The village of Kivalina is one of the most at risk and re-location to a higher elevation at great cost, seems to be the only option.  A further concern is whether an extended period of permafrost melting will release sequestered methane from the active layer, that is, the depth to which the soil melts in summer.  

Paul Schuster and his colleagues at the USGS have recently concluded a study that measured mercury concentrations in permafrost. His team estimated that 15 million gallons of mercury is sequestered in frozen soil and concluded that northern permafrost soils are the largest mercury reserve on the planet [1]. Warmer temperatures could release a large quantity of mercury into the atmosphere which could potentially affect ecosystems beyond Alaska.

Arsenic

Given the abundance of gold mining in Alaska it is not surprising that arsenic in groundwater is a concern for many communities. Fairbanks, the second largest city in the state, is located in the interior of the state and partly owes its existence to the discovery of gold in the Chena River in 1902. Gold-bearing veins are present in the Fairbanks area and are associated with the intrusion of granitic rocks in the Late Cretaceous. Placer deposits in gravel in the area has been dredged at one time or another, leaving a distinctive hummocky topography along the floors of the valley, with the occasional marooned dredge.  Kinross Gold operate the open pit Fort Knox mine north of Fairbanks, which has produced over 7 million ounces of gold to date. There are several active gold exploration projects in the area.

Gold Dredge Fairbanks

An abandoned gold dredge in Fairbanks

 

As a consequence of the mineralization and historical mining activity, arsenic is present in drinking water from wells all over the region, with concentrations as high as 1140 ppb. The Alaska Section of Epidemiology [2] reported that several residents had elevated urine arsenic as a result of consuming drinking water from this source. Fortunately, reverse osmosis treatment of drinking water at the well head to remove arsenic is highly effective.

The combination of world-class metal deposits and pristine wilderness is a potential recipe for conflict between proponents who wish to develop natural resources and environmentalists who are opposed to further development.  Mining projects are under intense scrutiny as they navigate the permitting process and scientists attempt to quantify impacts of development on wetlands, fish species and human health. A better understanding of the relationship between environmental geology and health is of great importance in making defensible decisions on whether to proceed.

If you haven’t visited Alaska it should be on your bucket list.



[1] Schuster, P. F., Schaefer, K. M., Aiken, G. R., Antweiler, R. C., Dewild, J. F., Gryziec, J. D., … Zhang, T. (2018). Permafrost stores a globally significant amount of mercury. Geophysical Research Letters, 45, 1463–1471. https://doi.org/10.1002/2017GL075571

[2] State of Alaska Epidemiology Bulletin No. 14, May 17 2016.

Photo credits: Keith Torrance

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