Monday Geology Picture: Old Maps of Africa

Several old maps of Africa on display. I love when maps are used as decoration! The skewness of these maps upsets my ODC tendencies, but in a way it also adds to the charm of the display!

Earlier this year I visited a local wine farm here in the Western Cape of South Africa, and there I saw a lovely display of some reproductions of some old maps of Africa. I’m not sure about the background of these maps, but I snapped a few pictures because I thought they were interesting. If you recognize any of the maps, please let me know in the comments.

Here are a couple of close-ups of the detailed map of the Cape Town area, where I live:

Cape Town area map #1. — Cape Town area map.

- View #2. — Cape Town area map – Close-up view.

If you look closely on the close-up view (click for a larger version), you can see that there are some useful descriptions on parts of the map. For example, there’s a description “Very Good Grounds” and then there’s a description “Grounds Not Fit for Tillage”. There are also some comments about the local mountain chains, with one being described as “Inaccessible Mountains” (I’ve corrected to modern spelling).

My husband and I live roughly in the “Grounds Not Fit for Tillage” part of the map, which probably explains why we struggle with our garden! The soil where we live is indeed very sandy and mostly comprised of quartz. Thus, it’s tough to grow anything other than local, native plants. So, we’ve planted a garden full of local succulents and are attempting this year to grow a few vegetables in a raised bed. We tried planting some flowers earlier this year, but only the ones in the pots (with special soil) seemed to survive!

I think that “Inaccessible Mountains” description may be fair, too. I’ve been on some tough hikes in that area!

I really enjoy old maps, and it’s great when they contain detailed information such as the Cape Town area map. I’d say that this map is still useful today!

Monday Geology Picture: An Early Map of Arabia

A Map of Arabia by Abraham Ortelli, circa 1570. Map print hanging in the Dubai Museum, September 2013. — Map of Arabia by Abraham Ortelius, circa 1570. Map print hanging in the Dubai Museum, September 2013.

Back in September 2013 I visited Dubai for one day during a layover when I was flying from Alaska back to South Africa. I was fortunate enough to be able to sleep on the flight from New York to Dubai, so when I arrived in Dubai I took a quick shower at the hotel then headed out to explore for a few hours. I spent some time at the Dubai Museum. The museum is located in a fort that is the oldest building in Dubai and has several interesting exhibits. I’ll blog a little more about my visit to the museum later this week.

For now, I want to share this picture of an interesting map that was displayed in a little nook in one part of the museum. As I was walking through the museum, the map caught my eye, so I took a picture of it. The map is titled “Map of Arabia in 1570 by Abraham Ortelius”. I was intrigued by the map as I thought that 1570 was quite early for such a detailed map to have been produced for the region. When I did some googling after the museum visit, I discovered that the map comes from a book known as the Theatrum Orbis Terrarum (Theatre of the World), which is considered to be the world’s first modern atlas. This atlas was compiled by Abraham Ortelius, a Flemish cartographer and geographer. I’ll have to do some reading on Ortelius– he sounds like he was a very interesting person. According to Wikipedia, he was apparently one of the first people (the first person?) to propose the theory of continental drift… long before Alfred Wegener!

A Famous Ocean Floor Map

The 1977 World Ocean Floor Map created by Bruce Heezen and Marie Tharp. Image taken from here.

One of the most famous world maps is the 1977 World Ocean Floor Map (see above) created by Bruce Heezen and Marie Tharp, a pioneering female oceanographer and kick-ass female scientist. Prior to the publication of this map, scientists had very little idea of what the seafloor looked like on a global scale.

Although the concepts of mid-ocean ridges and plate tectonics seem innate to the work of oceanographers and geochemists today, these concepts are remarkably recent in their development. Plate tectonics was not fully accepted by the scientific community until the late 1960s and early 1970s, and this first great seafloor map was not published until the late 1970s. Mid-ocean ridges were not discovered until the work of Heezen and Tharp in the 1950s and 1960s.

To this day, scientists still know relatively little about the seafloor. Modern technology is making mapping the seafloor easier, but to obtain detailed information one really must go out in a boat and take many days to carefully study a section of seafloor. Research cruises to map the seafloor are expensive and not always practical. Remote sections of the ocean or places where there is bad weather are difficult to impossible to map. Geologists actually know more about the topography of the moon and other terrestrial planets, such as Mars, than they know about the topography of Earth’s own ocean floor.

Prior to the pioneering work of Heezen and Tharp, almost nothing was known about the topography of the seafloor. The advent of new technologies to study bathymetry and the dedicated work of Heezen, Tharp, and other oceanographers shed some light on the dark, unknown ocean floor. Tharp carefully mapped the Atlantic ocean and discovered the Mid-Atlantic Ridge, a giant chain of mountains running along the middle of the ocean. At first, no one believed Tharp’s discovery of mid-ocean ridges. In the days before plate tectonic theories had been worked out and generally accepted, having a giant mountain chain in the middle of an ocean didn’t make much sense. There was no obvious reason why such a mountain chain should occur in the middle of an ocean.

Later, scientists realized that such ridges made perfect sense: mid-ocean ridges represent places where two oceanic plates are moving apart and new oceanic crust is forming from volcanic eruptions. At a mid-ocean ridge, the young, hot lava is bouyant and creates a topographic high. As the oceanic crust moves away from the ridge and ages, it cools and becomes more dense. The crust contracts and also sinks lower into the mantle, creating a topographic low. Thus, the ocean is shallower at mid-ocean ridges and deeper in the middle of oceans and also at subduction zones, places where the oldest, densest oceanic crusts subducts underneath lighter continental crust.

The famous 1977 seafloor map of Heezen and Tharp was a revolutionary map for the worldview of oceanographers. All of a sudden, oceanographers had an elegant, dramatic picture of the mid-ocean ridges running through the world’s oceans like seams on a baseball. The map made sense in the framework of the young science of plate tectonics.

Although new data on the seafloor has been collected using modern techniques such as multibeam bathymetry (bouncing waves off the bottom of the ocean to calculate topography) and satellite altimetry (using the height of ocean waves to look for gravity anomalies and infer the topography below), the 1977 Heezen and Tharp map is still remarkably accurate, especially considering they made up (honestly– they didn’t deceive anyone) parts of the map where they had no data.

Heezen and Tharp’s 1977 seafloor map is also remarkable for its aesthetic beauty. The map was actually painted by a famous landscape and panorama artist named Heinrich Berann, a very talented Austrian painter. Berann masterfully captured the dramatic mountain ranges of the mid-ocean ridges in his painting.

Bruce Heezen died many years ago, and Heinrich Berann died a few years back. Marie Tharp just died in 2006 at the age of eighty-six. Here’s to a great female oceanographer and scientist. I hope that my career in oceanography has a tenth of the influence Marie’s career did.

Bruce Heezen and Marie Tharp. Image from Wikipedia Commons.

Marie Tharp in 2001. From Columbia University Website here.