Geotimes — March 2004 — The Global Lakes Drilling Effort

Geotimes

Feature
The Global Lakes Drilling Effort
Douglas W. Schnurrenberger and Vance Hiatt

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 paleoclimate reconstructions.

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 world’s 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 Earth’s 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.

The gear

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 Earth’s 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 project’s 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 lake’s sensitivity to regional precipitation patterns and faithfully record changes in precipitation in the Great Basin for the past almost 300,000 years.

Lake Titicaca

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).

Englebright Reservoir

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.

Iceland

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 Iceland’s ice caps during the Late Glacial and Holocene periods.

Future projects

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 El’gygytgyn 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.

The 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.

Once a drilling rig and platform are positioned over the site, either with a four-point anchoring system in relatively shallow (less than 200 meters) water or by means of a dynamic positioning system in deeper waters, casing is hung from the drill rig and additional joints threaded onto lower ones until it sits just above the lake floor. Casing ensures that the drillers can reenter the hole if necessary and protects the relatively weaker drill pipe within it.

Next, DOSECC (Drilling, Observation and Sampling of the Earth's Continental Crust) drillers begin to lay the drill string inside the casing. The first component of the drill string is the outer core barrel. This hollow piece of steel is designed to accept the coring tools as they are lowered down via the wire-line. Additional pieces of drill pipe are threaded onto lower pieces until the core barrel is at the desired depth above the sediment water interface for the first shot.

Depth control is maintained by adding together the lengths of standard drill pipe plus the length of the core barrel as the drill string is put together. The depth to the sediment water interface is determined by means of a depthfinder (sonar device) or a weighted tape measure in shallow water. The driller has a large responsibility, both to maintain proper depth control and to ensure safety on the platform as heavy pieces of casing and drill pipe are raised and lowered in rapid succession.

Once the desired depth for the first shot is reached, the driller lowers the designated coring tool (for this description we will use the example of the hydraulic piston core, or HPC into the uppermost piece of drill pipe), which at this point is held aloft by a clamp operated by the driller. Next, the driller drops the coring tool: The tool falls at about 1 meter per second; with its descent slowed by water, it must displace in the drill pipe as it falls. The driller knows the coring tool has locked into place by hearing a metallic sound as the tool fits into position.

When the HPC is in position, the driller closes off the uppermost piece of drill pipe with a cap that contains a hose from which water is pumped into the drill pipe. The HPC is a composite tool with an inner and outer core barrel containing a plastic liner within the inner core barrel. The inner and outer core barrels are initially held together by metal shear pins (different metals such as aluminum or bronze with different shear strengths are used as necessary). A stainless steel rod is attached to the upper end of the outer core barrel and extends the length of the inner core barrel. A piston on the end of this rod fits snugly inside the plastic liner inside the inner core barrel.

Hydraulic pressure within the drill string will eventually cause the shear pins to fail, and the outer core barrel will shoot forward until its forward motion is halted by the piston rod attached to the outer core barrel. As the inner core barrel moves forward, the piston sucks sediment into the plastic liner. At its fullest extent, the inner core barrel and its plastic liner have moved forward and collected 3 meters of sediment.

The driller now shuts off the pump valve to reduce hydraulic pressure within the drill string. The upper cap is removed from the upper drill pipe (accompanied by an upward flow of water), and the wire line cable with the core tool catching device is lowered down until it sits on the top of the HPC. The driller then raises the HPC with the wire line cable until it is fully out of the drill pipe. At this point, the driller's helpers manually drag the now-6-meter-long HPC over to the core table, while the driller lowers the upper end, finally laying it flat on the core table.

The driller's job is now finished with that particular core, and the science crew takes over. The next steps involve removal of the cutting shoe from the bottom of the core barrel (with its included core catcher) and removal of the plastic liner from the inner core barrel. The science crew cuts the core liner into approximately 1.5-meter-long sections while the drilling crew cleans and reassembles the HPC for the next shot.

Typically a drilling program employs two HPCs. While one is being disassembled, cleaned and rebuilt, the driller loads the remaining tool into the drill string, drops it and begins to clean the hole using a combination of rotation of the reaming tool and jets of water. The driller attempts to clean the hole just down to the base of the previous shot. Once the hole is clean, a conference takes place between the scientists and the drillers to determine the proper depth of the next shot. Once they are in agreement, the driller drops the second HPC and prepares to take the next shot while the science crew is working with the first core.

The science crew cleans the liner and then caps both ends with plastic end-caps affixed with acetone and duct tape. A blue-end cap is placed on the core top and a clear cap on the lower end. The uppermost section is measured and cut to produce a 1.5-meter-long top section. The remaining liner (typically 1.42 meters) is capped and designated section 2. The sediment captured above and below the core catcher is extruded into a short piece of liner — typically measuring 0.08 meters, for a total 3-meter-long core.

The core sections are stored temporarily onboard the barge, either in a bin on the deck or in a cooler if conditions are warm. During shift changes, the core sections are transferred to a shore storage container and stacked on pallets for shipment to Minnesota. Once the project is over, the cores are either air-freighted or shipped in a refrigerated container to Minnesota.

Douglas W. Schnurrenberger

Schnurrenberger is curator of the National Lacustrine Core Repository located at the University of Minnesota in Minneapolis. He has participated in most of the GLAD drilling projects to date. Hiatt is a driller for DOSECC and has operated the GLAD drilling systems on all of the program’s projects. The authors gratefully acknowledge the support of the National Science Foundation.

Link:
"Lake Titicaca: An Archive of South American Paleoclimate," by Paul A. Baker, Sherilyn C. Fritz and Geoffrey O. Seltzer, Geotimes, December 2001

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