Mapping the deep: Marie Tharp’s physiographic diagram of the Atlantic Ocean

Manuscript painting of Heezen-Tharp’s “World Ocean Floor” map.
Heinrich C. Berann, 1977.
Geography and Map Division.

 

From LOC by Julie Stoner
 

This is a guest post by Colette Harley, a Junior Fellow in the Geography and Map Division.

My Junior Fellowship project this summer was entitled “Marie Tharp, Mapmaking Pioneer – Diving into Unprocessed Collection Material”.
As an archivist, my ears always perk up at the phrase “unprocessed material.” This is a bit of a catch-all term for materials that aren’t ready for researchers just yet.
Often, they are unsorted and under-described, which makes their usefulness for researchers limited.
I was also drawn to the work of Marie Tharp, an oceanographer and geologist, who created the first map of the Atlantic Ocean Floor in 1957.
Tharp’s collection is large and documents her career working at the Lamont Geological Observatory and her personal life, as well as the professional and personal papers of her long-time collaborator, Bruce C.
Heezen.

My task was to create an inventory of some of the oversized materials housed in flat files in the G&M stacks.
Much of the material was related to the process of map making – reference maps, graphs, earthquake and seismicity information, negatives of bathymetry and contour data, as well as ship course data.
The material ranged from plastic sheets to a specific copying process called Ozalid, which was used during this time for engineering diagrams and is akin to a white print.
I relied heavily on documentation created by Gary North, the original processor of the collection.
This documentation helped me to understand what these different data sheets were and how Tharp might have used them in her mapmaking.
The running count of the inventory is over 1,300 items, and this will be added to the collection so researchers can access these materials.

 

Detail from Physiographic diagram of North America; Physiographic provinces of North America.

A.K.
Lobeck, 1948.

Geography and Map Division.

Heezen and Tharp’s first published map was a physiographic diagram of the Atlantic Ocean floor, published in 1957.
Physiographic diagrams were first popularized by Armin K.
Lobeck and Erwin Raisz, and depict geological features as if looking at them from above and slightly sideways.
I was interested in these maps for their aesthetic appeal and uniqueness – I had never seen this type of map before.
Although their uses in actual wayfinding may be limited, these maps convey an overarching image of the place they depict almost instantaneously.

In thinking about maps, there is often a connection between form and function.
How a map maker depicts data on the map is often tied to its uses: a tourist map may have additional information about where to get a meal and precise locations are not as paramount.
When working with a nautical chart or topographic map where precise data or use is required, the map maker can choose the type of map best suited to that data and purpose.
Heezen and Tharp’s reasoning for picking this specific type of map is a confluence of history and practicality.

 

Physiographic Diagram of the Atlantic Ocean, Sheet 1.
Bruce C.
Heezen and Marie Tharp, 1957.
Geography and Map Division.

A primary reason for choosing a physiographic diagram versus a straight topographical map was the consideration of the Cold War.
Much of the data Heezen and Tharp utilized was considered classified and so the physiographic diagram was a way to depict the ocean floor without revealing the data they had used.
Additionally, data of the ocean floor was incomplete.
Research vessels often traveled in straight lines and did not acquire data for every square inch of ocean floor.
Thus, as Tharp completed the map, she relied on her training as a geologist to make educated guesses and fill in the missing data to complete the ridges.
Tharp and Heezen note the difficulty of mapping an un-seeable area in their book, The Floors of the Oceans: I.
The North Atlantic:

“There is a fundamental difference between the preparation of a terrestrial and a marine physiographic diagram… Except in unexplored, inaccessible areas, the shape of all land feature is a matter of recorded fact; the problem is to abstract and artfully draw the features in question.
In contrast, preparation of a marine physiographic diagram requires the author to postulate the patterns and trends of the relief on the basis of cross sections and then to portray this interpretation in the diagram.”

Much of this map relies on intuition, which without Tharp’s training as a geologist would have been very difficult.

 

Draft of a physiographic diagram.
Marie Tharp, undated.
Geography and Map Division.

A final reason for choosing this type of map was its ease of conveying data.
Viewers could look at the map, whether they were scientists, school children, or members of the public and understand the ridges and valleys that populated the ocean floor.
Prior to this map our understanding of what lay beneath the ocean was minimal.
This map depicts the bottom of the Atlantic Ocean as a complex and varied place, not just flat sand for thousands of miles.
It also outlined the Mid-Atlantic Ridge, a deep valley and mountain range that separates the North American plate from the Eurasian plate.
While creating this map, Tharp and Heezen overlaid seismicity and earthquake data on the map and realized that many of the earthquakes occurred along this ridge.
This map was a huge step forward in the acceptance of plate tectonics and continental drift, a controversial idea first proposed by Alfred Wegner in 1912.

Tharp and Heezen went on to create maps of much of the ocean floor, without computers or automation, and published several physiographic diagrams of the Atlantic, Indian, and Pacific Oceans.
They worked closely together until Heezen’s death in 1977 shortly after they had completed their first map of the ocean floor with artist Heinrich C.
Berann.
It was a pleasure to spend so much time with Tharp’s work and to learn from everyone in the Geography and Map Division this summer.

Links :

• View other blog posts and story maps from the LOC on Marie Tharp and mapping the ocean floor.
• Read Hali Felt’s biography of Marie Tharp, Soundings: The Story of the Remarkable Woman Who Mapped the Ocean Floor. 
• Explore the Heezen-Tharp Collection finding aids.
• GeoGarage blog : Geologist Marie Tharp mapped the ocean floor and helped / How pioneering geologist Marie Tharp changed our view of Earth / Marie Tharp's adventures in mapping the seafloor, in her ... / Marie Tharp: the woman who mapped the ocean floor / How one brilliant woman mapped the ocean floor's secrets / The great challenge of mapping the sea / The floor of the ocean comes into better focus