Happy ending for Franck Cammas and Charles Caudrelier and all the crew of the Gitana team
Links :
- GeoGarage blog : Rolex Fastnet 2019
Saturday, August 17, 2019
Friday, August 16, 2019
How underwater archaeology reveals hidden wonders
This Maya skull was found by underwater archaeologists in a sacred cenote, or natural sinkhole, in Mexico.
Photograph by Paul Nicklen, Nat Geo Image Collection
Photograph by Paul Nicklen, Nat Geo Image Collection
From National Geographic by Erin Blakemore
Curious about still-hidden archaeological treasures?
Just add water—that’s the concept behind the emerging field of underwater archaeology.
But don’t be deceived: It’s anything but simple, and recent advances have made it one of the most exciting forms of modern archaeological research.
It’s always been difficult to access sites under water, but there’s a particular allure to potential archaeological sites hidden under oceans, lakes, and rivers.
Shipwrecks are far from the only thing to document, study, and preserve underwater: there’s also everything from very ancient human remains to submerged settlements, like portions of ancient Alexandria, the Egyptian city that partially sank into the Mediterranean over the centuries.
Over the years, the relatively recent discipline of underwater archaeology (which really got going with the use of scuba in the mid-20th century) has branched off into a number of subdisciplines that look at everything from how humans interact with water to the search for airplanes that make water their final resting place.
And plenty of above-ground archaeologists eventually find themselves looking to nearby bodies of water for answers.
Finding an ancient Spanish shipwreck
Led by clues found in old documents, maritime archaeologist Robert Grenier makes a thrilling discovery.
Led by clues found in old documents, maritime archaeologist Robert Grenier makes a thrilling discovery.
Often, the hunt for underwater objects presents serious logistical and interpretive questions.
It can be expensive to look underwater at all, and researchers must recruit divers (who are often also archaeologists) with the ability to document and handle delicate objects appropriately.
Weather conditions and tides can stymie an expedition.
And once a site is located, it can be tricky to study.
Water is dynamic, and objects are susceptible to its ebb and flow.
It can break up materials and jumble them in a way that makes interpretation difficult.
Conservation can be even trickier; water can be hard on already delicate objects, and moving a newly recovered object is even harder when it’s underwater.
This illustration shows a remotely operated submersible used in underwater research.
Illustration by Richard Schlecht, Nat Geo Image collection
Luckily, archaeologists have plenty of technology to combat those challenges.
LiDAR can reveal structures and objects underwater and map sites; sonar, magnetometors, and other remote sensing devices can help, too.
Advanced photography and videography can bring sites to life even for those who’ll never venture into the water.
And a new generation of submersibles is driving new discoveries.
The R/V Petrel, for example, carries two onboard robots that have helped uncover 21 World War II vessels, including the U.S.S. Indianapolis.
Helping hands
Underwater archaeology also depends on good relationships with other communities familiar with the bodies of water they work in.
That became clear to researchers who were alerted to a large cache of shipwrecks near Fourni, Greece, by a local fisher.
The assistance of the area’s fishers ended up helping archaeologists discover 23 shipwrecks in the area in 22 days.
Volunteers can drive much of the field, as in Florida, where volunteers work alongside archaeologists.
Octavio del Rio examines a skull from a funerary deposit in northern Yucatan, Mexico.
Photograph by Wes C. Skiles, Nat Geo Image collection
Local and international laws also apply: UNESCO, the UN’s cultural arm, has established international law around underwater cultural heritage that mandates in situ (“in place”) preservation as the ideal option when researching a submerged archaeological site.
That means many underwater finds must be left where they were found.
This can add another layer of challenge for researchers who document sites with locations that may never be revealed to the public in order to prevent vandalism or looting.
Other sites do find public lives, as did Baiae, a Roman seaside resort that is now an underwater museum open to visitors.
Working under the waves is challenging, but it can offer rich rewards for those seeking to understand the past.
Links :
Thursday, August 15, 2019
How pioneering geologist Marie Tharp changed our view of Earth
Oceanic cartographer Marie Tharp helped prove the theory of continental drift with her detailed maps of the ocean floor.
This animation by Rosanna Wan for the Royal Institution tells the fascinating story of Tharp’s groundbreaking work.
From Forbes by David Bressan
Marie Tharp was born on July 30, 1920, in the city of Ypsilanti, Michigan.
As a young girl she followed her father, a soil surveyor for the United States Department of Agriculture, into the field.
She also loved to read and wanted to study literature at St.
John's College in Annapolis, but women were not allowed to join the courses.
So she went to Ohio University, where she graduated in 1943.
Marie Tharp used hundreds of seismic profiles to reconstruct the topography of the seafloor, like here of the Atlantic Ocean.
Lamont-Doherty Earth Observatory, Marie Tharp
She worked for a short time in the petroleum industry, but found the work unrewarding and decided to resume her studies at Tulsa University, Oklahoma.
In 1948 she graduated in mathematics and found a job at the Lamont Geological Laboratory at Columbia University.
At the time the U.S. Navy was interested in mapping the seafloor, believed to be of strategic importance for future submarine warfare.
Marie started a prolific collaboration with geologist Bruce Charles Heezen, a specialist for seismic and topographic data obtained from the seafloor.
As a woman, Marie was not allowed to get on board the research ships.
Instead, she interpreted and visualized the collected data in her laboratory, producing large hand-drawn maps of the seafloor.
By interpolating and plotting the echo soundings of the seafloor collected from the research ship in 1957 Marie Tharp noted the strange bathymetry of valleys and ridges of the mid-Atlantic ridge.
The existence of a ridge under the Atlantic Ocean was discovered during the expedition of HMS Challenger in 1872, taking depth measurements across the ocean.
In 1925 it was confirmed by sonar that the ridge of unknown origin extends around the Cape of Good Hope into the Indian Ocean, making it one of the most extended mountain range on Earth.
Marie Tharp suggested that the mid-ocean ridges had "rift valleys" running along their axes where new crust is formed, pushing apart blocks of older crust, forming the ridges.
Her idea dismissed at the time as "girl talk" by one of the expedition's leaders.
Original sketch by Tharp of the seafloor in the Mid-Atlantic.
Between 1959 and 1977 she continued to work on various large-scale maps that would depict the still mostly unknown bathymetry of the seafloor.
Not too many people can say this about their lives: The whole world was spread out before me (or at least, the 70 percent of it covered by oceans).
I had a blank canvas to fill with extraordinary possibilities, a fascinating jigsaw puzzle to piece together: mapping the world’s vast hidden seafloor.
It was a once-in-a-lifetime—a once-in-the-history-of-the-world—opportunity for anyone, but especially for a woman in the 1940s.
The nature of the times, the state of the science, and events large and small, logical and illogical, combined to make it all happen.
This animation portrays the motion of continents (grey, yellow, orange and red) and oceanic plates (blue) since Pangea breakup from 200 million years ago.
The model is a modified version of the Seton et al. (2012) plate reconstruction, and is used to analyse factors affecting plate velocities in Zahirovic et al. (2015).
The results indicate that continental keels slow down plate velocities, where Archean cratons (red) have the strongest effect in limiting plate speeds.
cortesy of EathByte, University of Sydney
cortesy of EathByte, University of Sydney
The seafloor was not a series of muddy plains, as previously imagined by most geologists, but instead featured mountains, ridges and canyons, sometimes larger and deeper as any example found on the continents.
Along the mid-ocean rifts, molten rock rises up from Earth's mantle, pushing and pulling apart the oceanic crust.
This mechanism is not limited to the oceans but also involves the continents and is the driving force behind plate tectonics.
Links :
- GeoGarage blog : Marie Tharp: the woman who mapped the ocean floor / If the ocean was transparent : the see-through sea / How one brilliant woman mapped the ocean floor's ... / The floor of the ocean comes into better focus / Floor of the World Ocean, Harrison 1961 vs Garcia ... / The great challenge of mapping the sea / Secretly mapping the sea floor / Why the first complete map of the ocean floor is .. / The quest to map the mysteries of the ocean floor
Wednesday, August 14, 2019
Canada (CHS) layer update in the GeoGarage platform
25 nautical raster charts have been updated & 3 new charts added
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