Although lakes are,
geologically speaking, temporary features of the landscape, many lakes across
the globe have been accumulating sediment for millions of years. The potential
sedimentary archives in these ancient lake basins are often continuous, with
no hiatus in sediment accumulation, and of high temporal resolution, with sedimentation
rates in excess of one centimeter per year thus permitting the study
of phenomena at annual to decadal scales. Additionally, lakes respond to forcings
on a local to regional scale, lending a high degree of spatial resolution to
The GLAD200 drilling rig recovers sediment from Hvitarvatn, Iceland, in the summer of 2003. Courtesy Douglas W. Schnurrenberger.
A long history of research on relatively young lake basins illustrates the utility of studying lake sediments for information on such diverse topics as past climate, landscape modification, biological evolution, regional tectonics and hydrocarbon formation.
Obtaining long sedimentary records from lacustrine basins has been difficult, however, due to the logistics of mounting a drill rig on a platform capable of drilling hundreds of meters below a lake floor in deep waters. The cost of mounting such site-specific campaigns has restricted the scientific drilling of lakes to only a few promising examples.
Researchers have drilled Lake Biwa in Japan several times, with one hole reaching 1,400 meters depth. Researchers have also drilled Lake Baikal in Siberia, the worlds deepest lake, from the stable platform provided by lake ice. While these projects illustrated the scientific value of lake drilling, they also proved the difficulty in such an endeavor. Each project was forced to rent equipment from commercial drilling firms and essentially reinvent the wheel in terms of recovering high quality cores from largely unconsolidated sediment.
In the fall of 1999, a small group of scientists and drilling engineers held a two-day meeting to brainstorm the construction of a mobile drilling platform that could rapidly and inexpensively be deployed to many of Earths large lakes. One of the leaders of this group, Kerry Kelts of the University of Minnesota, coined the term GLAD (Global Lakes Drilling) as the acronym for this effort. By September 2000, the concept moved from the drawing board to reality, with holes drilled more than 100 meters deep in both the Great Salt Lake in Utah and Bear Lake in Utah and Idaho.
At the same time that planning for drilling became a reality, the research team realized that existing facilities for core handling, documentation and archiving were inadequate for the number of core meters anticipated from coring expeditions. Therefore, in anticipation of the first GLAD drilling in the Great Basin, Kelts, Emi Ito and Doug Schnurrenberger, all of the University of Minnesota, along with Tom Johnson of the University of Minnesota, Duluth, set out to construct and operate a core repository known as LacCore (National Lacustrine Core Repository), with funding from the National Science Foundation (NSF).
Situated on the University of Minnesota campus in Minneapolis, LacCore has been in operation since the summer of 2000 and currently archives 2,000 meters of lacustrine core sections, providing more than 15,000 samples for study to scientists and educators.
To date, the GLAD program has explored seven lakes in four projects worldwide. Funded through the International Continental Drilling Program (ICDP) and several national agencies including NSF, GLAD operates two primary workhorses for lake drilling: the GLAD200 and GLAD800 drilling rigs. (The numbers in each name refer to the optimal lengths in meters of total drill string recommended for each system.) Drilling equipment, platforms and expertise for GLAD projects are owned and operated by DOSECC (Drilling, Observation and Sampling of the Earths Continental Crust), a nonprofit, NSF-sponsored corporation operated by a consortium of 51 research organizations.
Lake drilling can involve coring through soft, unconsolidated lake muds as well as gravels and ultimately carbonate or crystalline rock, depending on the projects objective. To address these issues, DOSECC engineers have designed a palette of coring/drilling tools to optimize sediment recovery and to facilitate recovery of a wide range of sediment and rock types. The primary tool for unconsolidated lake mud is the hydraulic piston core, which acquires a 3-meter-long core by being hydraulically forced into the mud. As the consolidation of the sediment increases, drillers may opt to employ the non-rotating extended shoe coring tool, in which a non-rotating core barrel with liner is forced to advance while an outer rotating core barrel cuts into the sediment. Finally, when encountering rock, drillers employ a rotating extended core bit that cuts into the rock and produces a solid core.
Great Salt Lake and Bear Lake
In August 2000, the GLAD program opened with scientific drilling and engineering tests on the Great Salt Lake and Bear Lake. Headed by Kelts, the GLAD1 project involved the collaboration of both academic and government researchers. Holes drilled in the two lakes achieved depths in excess of 120 meters. Attempts to drill deeper (down to 400 meters) in Great Salt Lake were thwarted by nightly storms blowing the platform off the hole (in shallow water there is less room for horizontal displacement) and, ultimately, funds.
One site at the Great Salt Lake penetrated two salt beds of 3- and 6-meters thickness, indicating near total desiccation of this large yet shallow water body. Uranium-thorium age estimates, determined by Hai Cheng and Larry Edwards of the University of Minnesota, indicate a basal age of the hole in excess of 280,000 years. The two salt beds are believed to represent lake desiccation during the last interglacial and possibly during the Younger Dryas interval around 10,500 years ago.
The two thick salt beds bracket another sedimentary package unit, which records a deep freshwater lake, known as Lake Bonneville. Lake Bonneville rose to its maximum height about 1,000 feet above the modern lake level approximately 17,000 years ago. These dramatic fluctuations in lake level reflect this lakes sensitivity to regional precipitation patterns and faithfully record changes in precipitation in the Great Basin for the past almost 300,000 years.
Scientific drilling on Lake Titicaca (GLAD2) took place in 2001, under the direction of Paul Baker of Duke University, Sheri Fritz of the University of Nebraska and Geoffrey Seltzer at Syracuse University. The project involved drilling three sites over one month at nearly 4,000 meters elevation in the Bolivian Altiplano (Geotimes, December 2001).
Cores recovered from Lake Titicaca document a series of glacial advances and lake-level changes producing laminated carbonate muds during times of low water and massive, gray, silty beds during periods of higher lake level and expanded glaciers in the surrounding highlands. These cores are still being analyzed but will yield information about the timing and nature of late Pleistocene climate events in the Andean Altiplano and, ultimately, the Amazonian rainforest (the source of much of the precipitation reaching Lake Titicaca).
Drilling at the Englebright Reservoir on the Yuba River in northern California (GLAD3) took place in summer 2002, using the newly designed GLAD200 drilling system with funding by the U.S. Geological Survey (USGS).
The Englebright Reservoir was constructed in 1941 to impound hydraulic mining waste. The goal of this drilling, led by Charlie Alpers of the USGS Water Resources Division in Sacramento, was to study the possible impact of mining-related pollutants in the stream sediments beneath the reservoir and the feasibility of restoring the stream to its original status as an anadromous fish stream. Approximately 300 meters of core from 22 holes at seven sites were recovered, which will be studied to determine the composition of the sediments, their age and possible contamination by mercury and gold.
In June/July 2003, drilling of three Icelandic lakes Hestavatn, Hvitarvatn and Haukadalsvatn occurred using the GLAD200 drilling rig mounted on a custom-built barge. This GLAD4 project was a collaboration between Gifford Miller at the University of Colorado, Boulder, and Aslaug Geirsdottir of the University of Iceland. It provided the challenge of moving the entire rig and barge to each of the lakes, one of which involved coring in front of an actively calving ice margin off the Langjökull icecap. Funded by NSF and the Icelandic Research Council, the goals of this project were to produce well-dated records of growth and retreat of Icelands ice caps during the Late Glacial and Holocene periods.
As of January 2004, two other GLAD projects have been funded for drilling on Lake Bosumtwi in Ghana and Lake Malawi in Malawi (GLAD5 and GLAD6). Proposals are also in preparation for submission to the ICDP to fund drilling efforts on Lago Peten Itza in Guatemala and Lake Elgygytgyn in Siberia.
Future GLAD projects will add to the expertise and capabilities of the GLAD core recovery teams. Drilling in Guatemala and Ghana is expected to include the recovery of cores specifically to study the nature of microbial life forms in the deep subsurface and their significance and role in biologically mediated geologic processes. Coring and drilling deep into Lake Malawi will entail use of a dynamic positioning system to maintain position over the hole as the lake is far too deep for anchoring. The drilling of meteorite-impact-crater lakes in Ghana and Siberia will add new challenges, as drillers and scientists attempt to drill deep into the impact rocks underlying the lake sediments.
With publication of results from prior GLAD projects and the exciting new projects still in the planning stages, the future of the drilling program looks bright. Investigators interested in learning more about the capabilities and use of the GLAD drilling system are encouraged to contact DOSECC, ICDP and their national funding agencies.
Life of a Core
The process of recovering a core from deep beneath the water's surface
is a mysterious process to those who have never witnessed it, and a dangerous,
difficult task for those who undertake it on a daily basis. The following
description chronicles a lake core from the process of its recovery through
its initial phase of analysis at the National Lacustrine Core Repository,
or LacCore, in Minneapolis, Minn.