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Project Mohole

Commemorating the Accomplishments of Project Mohole -- 1961-2011

Project Mohole represented the Earth sciences' answer to the space program. It was an attempt to retrieve a sample of the Earth's mantle by drilling a hole through the Earth's crust to the Mohorovicic Discontinuity, or Moho, which lies between the two layers. The National Academy of Sciences undertook this extremely ambitious project for its scientific potential. What began as an almost unfathomable idea grew into a popular project in which the Academy nurtured the concept and sponsored the feasibility phase. In April 1961, the project succeeded in drilling farther into the Earth's crust than ever before.

To tell the story of Project Mohole and celebrate the 50th anniversary of its achievements, we present a unique collection of photographs, video, original narratives, and historical documents.


Site Highlights:


Willard Bascom's original drawing illustrating the planned Mohole in relation to the deepest oil well and surrounding geographical features.
Project Mohole was an attempt to retrieve a sample from the Earth's mantle by drilling a hole through the Earth's crust to the Mohorovicic Discontinuity, or Moho. The project was suggested in March 1957 by Walter Munk, NAS member (1956) and member of the National Science Foundation (NSF) Earth Science Panel. The project's objectives were outlined in a proposal of December 1957 [PDF] by American Miscellaneous Society (AMSOC) member Harry Hess (NAS 1957).

Project Mohole represented, as one historian has described it, the Earth sciences' answer to the space program. If successful, this highly ambitious exploration of the intraterrestrial frontier would provide invaluable information on the Earth's age, makeup, and internal processes. In addition, evidence drawn from the Moho could be brought to bear on the question of continental drift, which at the time was still controversial.

The Mohorovicic Discontinuity -- named for Andrija Mohorovicic, a Croatian geologist who first proposed its existence -- marks the boundary between the Earth's crust and mantle. The plan was to drill to the Moho through the seafloor at those points where the Earth's crust is thinnest. Attempting such an effort on land would have been impractical, since the drilling equipment would not have withstood the depths and temperatures involved. Ocean drilling offered a further advantage in that undersea samples, unaffected by atmospheric and surface impacts, would provide better evidence of long-term geological activity than would samples drawn from land.

The American Miscellaneous Society

 "Walter Munk suggested that they should consider what project, regardless of cost, would do the most to open up new avenues of thought and research. He thought that sampling the Earth's mantle would be most significant."
-Willard Bascom, in remarks at the Symposium Commemorating the 25th Anniversary of the Demonstration of the Feasibility of Deep Ocean Drilling, 1989

Members of the AMSOC Committee, from left to right: Harry Ladd, Leonard S. Wilson, Harry Hess, Arthur Maxwell, Joshua Tracey, Linn Hoover, Gordon Lill, Edward Espenshade, Willard Bascom, William Thurston, Harold Saunders, William Heroy, James Balsley, and Lt. Col. George Colchagoff
The American Miscellaneous Society (AMSOC), which suggested drilling to the mantle, was an informal group of scientists formed in 1952 by Office of Naval Research geophysicists Gordon Lill and Carl Alexis. Lill and Alexis came up with the idea for AMSOC when they found themselves handling research proposals that fit into no existing scientific categories. Out of that "precarious miscellany," AMSOC emerged as a forum for scientific speculation.

At an AMSOC breakfast meeting, Walter Munk, a Scripps Institution of Oceanography geophysicist, proposed his idea for sampling the Earth's mantle. The society endorsed this idea, and by September 1957, members Roger Revelle (NAS 1957) and Tom Gaskell had persuaded the International Union of Geodesy and Geophysics to adopt a resolution that "urged the nations of the world to drill to the Moho Discontinuity."

In early 1958, the National Science Foundation agreed to provide $15,000 in initial funds for the project. The National Academy of Sciences became the sponsor of Project Mohole when in April 1958, with Academy assent, the AMSOC Committee of 14 was made a full-fledged unit of the Division of Earth Sciences of the National Research Council, the Academy's operating arm.

The Cuss 1 Drilling Ship
In 1958 a meeting of geophysicists was held in the great hall of the National Academy of Sciences building to discuss the AMSOC plan. Transcripts from that meeting show three main points of opposition. The first argument was that the sample taken from one hole could not be expected to represent the entire mantle, and that 10 or even 100 holes were needed. To which Harry Hess, then chairman of the Research Council's Earth Sciences Division, answered, "Perhaps it is true we won't find out much about the Earth's interior from one hole, but if there is not a first hole, there cannot be a second, or a tenth or a hundredth hole. We must make a beginning."

A second objection was raised regarding the expense. No one was yet able to give a reasonable estimate, and some worried that the project would strip funding from other Earth sciences projects for years. Roger Revelle answered with a historic example -- Columbus securing financing to sail west to India -- to illustrate that no great discovery has ever been without cost.

The third objection introduced a question of whether it was even possible to undertake a drilling operation in deep water. In answer to that, A.J. Field (NAE 1974), an engineer from Union Oil Company, showed movies of the converted Navy barge CUSS I -- a vessel equipped with a full-sized drilling rig working off the California coast in 200 feet of water. The CUSS I would go on to play a significant part in the Mohole effort.

Until that point, ocean drilling technology was a closely guarded secret of the oil companies. Virtually no one at the meeting had seen or heard of such equipment before, but they could see that it represented a new sort of tool which looked as though it could be developed into a deep-sea drilling rig. A wave of enthusiasm went through the audience and they saw the project in a new light. One audience member declared, "if American technology can go this far, it can drill to the Moho."

First Phase of Project Mohole: CUSS I Drilling Ship

Willard Bascom sitting on one of the four massive outboard motors, used to hold the ship steady for drilling
When funds for Project Mohole had been obtained from NSF, AMSOC in 1958 took charge of the effort. Lill chaired the committee, which included oceanographic engineer Willard Bascom as executive secretary and head of the technical staff. As Bascom recalled it:

"Behind the scenes the work was proceeding nicely, but by October the committee was becoming disturbed about the misinformation reaching the public. Rumors were flying that made deep-sea drilling sound more like science fiction than science. It was decided to scotch these wild rumors with a complete public statement for, by then, possibilities had narrowed, and our thoughts on how the work should proceed were more orderly. At least the committee could say with reasonable certainty what the scientific objectives were, which drilling sites seemed the most promising, and what kind of equipment might be used. The result was an article in the Scientific American (April 1959) written by me and titled 'The Mohole,' which summarized our thinking at the time."

The research vessel Horizon, which delivered the buoys to orient the CUSS I's positioning system
In September 1959, the AMSOC Committee released the report, "Drilling Thru [sic] the Earth's Crust: A Study of Desirability and Feasibility of Drilling a Hole to the Mohorovicic Discontinuity." The report reviews the feasibility of the project, including drilling sites and rig capabilities, and lays out a basic three-phase plan.

Phase I involved modifying a drilling vessel for deep-water operations. In part to test the equipment and obtain engineering design data, holes were planned for at least two locations using a variety of techniques. The scientific objective of Phase I was to core as deeply as possible into the ocean bottom. The second phase consisted of an intermediate vessel program, and the third would culminate with the final drilling to the Mohorovicic Discontinuity.

The crew of the Horizon lowers the buoys into the water.
The vessel used for Phase I was the same barge shown to the geophysicists meeting at the Academy in 1958 -- the CUSS I. Named for an engineering study committee sponsored by the Continental, Union, Shell, and Superior oil companies, the CUSS I was a surplus Navy freight barge converted in 1957 for offshore oil drilling. For the Mohole Project, the ship was modified to include experimental deep-water drilling gear and a newly devised system for holding it on station. The system, designed by Bascom, consisted of four huge outboard motors to hold the ship steady, thus preventing it from moving so much that its drill string would break. The ship's heading was to be monitored by gyrocompasses and controlled from a joystick mounted on a console. Its position would be determined in relation to a set of buoys, designed by Pete Johnson of the AMSOC technical staff (read his account here), set out in a circular pattern. As Bascom put it, "It occurred to me that if a ship were equipped with maneuvering propellers and if the pilot had a fixed reference point such as a piling or buoy to guide him, he could maneuver indefinitely to hold the ship within a small area." Bascom's new dynamic system for positioning the CUSS I represented a technological breakthrough by allowing stable drilling at depths for which anchoring would be problematic.

After ocean-going trials off La Jolla, California, Phase I began in earnest with a set of drilling experiments near Guadalupe, Mexico, in March and April 1961. The research vessel Horizon laid down the buoys to orient the CUSS I's positioning system, after which CUSS I took up station. Five holes, one of which extended 601 feet beneath the seafloor, were drilled under 11,700 feet of water. Cores obtained from the holes showed that the first layer of crust extended 557 feet and consisted of sediment Miocene in age. The second layer of crust was sampled for the first time, and, at this location, was found to consist of basalt. The Guadalupe operation and its results were documented in the report, "Experimental Drilling in Deep Water at La Jolla and Guadalupe Sites."

Phase I was not only a scientific success, but a triumph for the AMSOC Committee's technical staff, who were responsible for engineering solutions to the novel problems the operation raised. The technical staff's involvement in the Guadalupe operation was hands-on, as they provided direct scientific supervision aboard ship. Read the ship's log here.

On April 8, 1961, President Kennedy sent the following telegram to Dr. Detler Bronk, president of the National Academy of Sciences and Dr. Alan Waterman, director of the National Science Foundation:


I have been following with deep interest the experimental drilling in connection with the first phase of Project Mohole. The success of the drilling in almost 12,000 feet of water near Guadalupe Island and the penetration of the oceanic crust down to the volcanic formations constitute a remarkable achievement and an historic landmark in our scientific and engineering progress.

The people of the United States can take pride not only in the accomplishment but in the fact that they have supported this basic scientific exploration.

I extend to you my congratulations and ask that you pass them on to the special committee and staff of the National Academy of Sciences, the National Science Foundation, and Global Marine Exploration Company, and especially to all those onboard the CUSS I and attendant vessels who have combined their talents and energies to achieve this major success.



Phase II and Subsequent Discontinuation

After the unprecedented success of Phase I, the AMSOC Committee turned its attention to the design of a new drilling ship. The committee was divided, however, on whether this ship should be an "intermediate ship" or the final vessel that would eventually drill down to the Moho. AMSOC did agree that such a large-scale engineering and operational drilling program was beyond the scope of the National Academy of Sciences, primarily an academic entity. In preparation for the follow-on work, the AMSOC Committee supported and published a staff report, "The Design of a Deep Ocean Drilling Ship," which incorporated the lessons from the Guadalupe tests and included a proposal for an intermediate drilling ship as a next step.

After some controversy among supporters and participants, NSF assumed operational control and solicited proposals from industry. In 1962 a contract to drill the Mohole was awarded to Brown & Root of Houston. The projected undertaking was understood to be a difficult one. A.R. McLerran -- then an independent consultant for Brown & Root -- explained that at the time, "the deepest hole that had ever been drilled on land was about 27,000 feet. They [Brown & Root] were faced with the problem of trying to design a system to drill 35,000 feet from a bobbing platform out in the ocean that could maintain a station over the drill site and survive a 100-year hurricane."

Solving that problem meant tackling several unforeseen engineering challenges. In meeting those challenges, a great deal of research and technology were produced, much of it still in use in ocean drilling today. Unfortunately, the challenges also meant lengthy delays and cost overruns. Original estimates had priced the project at around $14 million; later that estimate grew to more than $150 million. After investing $57 million in the project, Congress denied further funding, and it was terminated.

Contributions of Project Mohole

This enlarged view of a cut and polished section of a one-inch core of glassy basalt resulted from experimental drilling for Project Mohole. This sample contains many very small veins of dolmite, zeolite, and several hydrated alteration products. Photo by U.S. Geological Survey.

Although Project Mohole did not achieve its ultimate aim of drilling to the mantle, it did contribute much to scientific knowledge of the Earth's makeup and processes, fostered progress in deep drilling techniques, and laid the groundwork for an ongoing scientific ocean drilling program.

Geological Samples

Mohole proved that deep-ocean drilling was a viable means of obtaining geological samples. The project retrieved, for the first time, a sample of the second layer under the softer sediments of the ocean floor. This layer, whose presence had previously been indicated to scientists only by reflections of seismic soundings, was revealed as basalt, a hard rock formed by the solidification of molten material within the Earth. The finding of basalt, which we now know continuously pours from fracture zones on the ocean floor, provided a major piece of evidence supporting the theory of continental drift.

The joystick control for the four outbound motors designed to hold the drilling ship in place.
Dynamic Positioning System

As described above, the problem of restraining the movement of the drilling ship was one that needed to be solved before any drilling could take place. Bascom's Dynamic Positioning System represented a conceptual and engineering breakthrough that was crucial to the success of Phase I. Read his plan for the dynamic positioning system here [PDF].

Workmen check drilling pipe guide shoe during installation beneath the hull of the CUSS I. Shoe acts to limit bending of the drill pipe at the hull bottom.
The Guide Shoe

One problem inherent in deep-water drilling is that the length of drill pipe near the water's surface is liable to bend, and subsequently kink, when combined with the tension generated by its own weight, as well as the motions of the drill ship. Preventing this from happening would be critical to successful drilling. The solution was found by Edward Horton (NAE 2002), a petroleum engineer on the AMSOC staff. Horton devised a funnel-shaped tube called a "guide shoe," through which the drill pipe passed on its way out of the ship and which constrained the pipe from bending excessively.

The Landing Base and Tapered Casing

A second potential site for bending stress to affect the drill pipe is on the seafloor. Here again a solution was needed to keep the pipe from kinking. It came in the form of a "landing base," a hexagonal seafloor steel structure with a tapered casing above and a standard casing below it. The entire structure was lowered to the seafloor with the drill pipe, then drilled into the bottom, and then disconnected from the drill pipe, allowing the pipes to continue to drill a deeper hole. As its name implies, the landing base provided a foundation for the pipe on the seafloor and the tapered casing prevented the pipe from over-stress bending where it entered the seafloor.

Although phases two and three of Project Mohole were not completed, it remains a significant milestone in the history of Earth sciences and laid the groundwork for future deep-ocean drilling projects. A truly pioneering project, Mohole provided a better determination of the age of the Earth, its history and internal constitution, the distribution of elements, and new insight into then-controversial theories of continental drift.

Resources for Further Study

An artist's rendering of what the ocean floor drilling equipment might look like. This design was significantly different from the system that was actually used.



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National Academies Reports



Notable Media Coverage



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Mohole's Impact on Pop Culture