Matt Herod

The Search for Ithaca

Matt Herod July 21, 2014

This post unifies two of my absolutely favourite topics: geology and classical Greek history. I have always had a soft spot for the classics. In fact, when I started my undergrad I was planning on doing a double major of geology and classics. I decided to focus on geology, but I have not lost my love of ancient civilizations particularly the ancient Greeks and Romans.

Odysseus (Source: Wikipedia)

Most of us are familiar with the story of the Odyssey, but I’ll recap it here briefly. The Odyssey is the tale of Kind Odysseus’s journey back from Troy to his home island of Ithaca. Odysseus, despite being a pretty shrewd guy, angers the god Poseidon who condemns him to wander the ocean for decades before he can go home. During this time Odysseus experiences many wild adventures in is quest to return home to his wife, Penelope and his son, Telemachos. Eventually, Odysseus returns home, but just in time to prevent his kingdom falling into rival hands. It is a classic good guy triumphs over evil tale and one of the best classical poems ever written. Homer obviously took substantial creative licence in the poem, as was customary at the time, however many of the places he mentions are real, as are the people such as Agamemnon, Menelaus, Troy, Mycenae, Sparta, etc. However, there has always been a question…where is Ithaca?? Indeed, Ithaca was missing. The home of the principle character in the poem was nowhere to be found and this just doesn’t jive with the accurate nature of rest of the poem.

This is a question that had baffled classical scholars for decades. At first, many believed that Homer just made up Ithaca since at that time Troy was believed to be fictional as well. However, once Troy was discovered it no longer made sense to think that Ithaca was made up and therefore, it must be some place amongst the Greek islands.

The passage in the Odyssey that describes the location of Ithaca is as follows:

εἴμ’ Ὀδυσεὺς Λαερτιάδης, ὃς πᾶσι δόλοισιν

ἀνθρώποισι μέλω, καί μευ κλέος οὐρανὸν ἵκει.

ναιετάω δ’ Ἰθάκην ἐυδείελον: ἐν δ’ ὄρος αὐτῇ

Νήριτον εἰνοσίφυλλον, ἀριπρεπές: ἀμφὶ δὲ νῆσοι

πολλαὶ ναιετάουσι μάλα σχεδὸν ἀλλήλῃσι,

Δουλίχιόν τε Σάμη τε καὶ ὑλήεσσα Ζάκυνθος.

αὐτὴ δὲ χθαμαλὴ πανυπερτάτη εἰν ἁλὶ κεῖται

πρὸς ζόφον, αἱ δέ τ’ ἄνευθε πρὸς ἠῶ τ’ ἠέλιόν τε,

I am Odysseus, Laertes’ son, world-famed

For stratagems: my name has reached the heavens.

Bright Ithaca is my home: it has a mountain,

Leaf-quivering Neriton, far visible.

Around are many islands, close to each other,

Doulichion and Same and wooded Zacynthos.

Ithaca itself lies low, furthest to sea

Towards dusk; the rest, apart, face dawn and sun.

Od 9.19-26 (text from http://www.odysseus-unbound.org/PDFs/How_did_Homer_describe_Ithaca_ENG.pdf)

So there you have it in beautiful Homeric Greek. The location of Ithaca…it is the westernmost of the Greek islands, which today is Cephalonia, formerly known as Sake, and not Ithaca. As for the current Greek island called Ithaca it in no way meets the description of Homer’s Ithaca and therefore it cannot be the same island, unless Homer was trying to play a massive joke on us all or did not understand basic geography, neither of which is very likely. So where did ancient Ithaca go?

Over the past few years a new theory has emerged to answer this question. In short the idea is that the thin isthmus of land between Paliki and the rest of Cephalonia was at one point underwater separating the two places and resulting in two islands. Indeed, there is classical text to back up such and idea. Strabo, the renowned ancient geographer wrote “where the island is narrowest it forms an isthmus so low-lying that it is often submerged from sea to sea.” If we trust Strabo, this means that during classical times there were actually two islands that are now one. Perhaps, westernmost Paliki was Ithaca during Homer’s time and the current island called Ithaca was another island was Doulichion. However, how can we prove that this idea is more than just an interesting theory?

Elevation map of Cephalonia. The white test is the current names and the yellow text is the name in Homer’s time. (Source: Odysseus Unbound)

Well, to answer this question we must turn to geology…we had to get there sometime.

The geological investigation of Stabo’s channel, now known as the Thinia valley, is being carried out by John Underhill, a professor of seismic and sequence stratigraphy in the University of Edinburgh department of geosciences. The geological evidence that Strabo’s channel existed is outlined in a paper by Dr. Underhill published in Nature Geoscience and is freely available online. However, I’ll give a brief outline of the evidence here.

In order to prove that Paliki was once an island the geology must show that the Thinia valley was once under water. However, the problem is that the elevation of the Thinia valley is 180m above sea level…and sea level certainly has not changed 180m is only 3000 years!!! However, there are other geologic features that can account for some of the uplift. The Eastern side of the Thinia valley is divided by a large thrust fault known as the Aenos Thrust, which is an extremely active fault to this day. Indeed, the last major earthquake on Cephalonia was a 7.2 magnitude in August 1953. The seismicity is generated by the collision of the Eurasian plate with the African plate. However, the earthquakes, while they cause substantial uplift did not occur often enough or have enough displacement to result in over 180m of uplift since the time of Homer. Therefore, another mechanism is needed to fill in the valley and raise it to 180m. Mapping of the island and the valley revealed a possible solution to this problem. The mapping revealed the occurrence of several large landslides and rockfalls in the valley. In fact, large blocks from the valley walls are easily observable within the valley. These massive landslides and rockfalls were caused by the earthquakes and storms and a lot of material fell from the steep valley walls into the valley.

A resitivity survey of the Thinia valley. The blue is Cretaceous bedrock, red is water, and the green and yellow are unconsolidated sediments. (Source: Odysseus Unbound)

To further prove the existence of Strabo’s channel, however, direct evidence of marine sediments must be observed underneath all of the landslide fill. In order to do this Underhill’s team drilled numerous boreholes around the valley and found many places where there was indeed marine sediment. In addition to drilling they also conducted geophysical surveys in order to map the subsurface geology of the valley in greater detail, which would allow them to map the channel and prove that it actually separated Paliki from the rest of Cephalonia. The geophysical techniques allowed them to determine the amount of fill in the valley from landslides, the depth to bedrock and the bedrock contours. Further surveys also revealed that there were drainage features in the sediment of the embayments on either side of the valley which shows that water flowed into the sea through the valley. Combining the boreholes, and the geophysical mapping all of the evidence points to the fact that Strabo’s channel did exist 2000-3000 years ago and that since that time uplift from earthquakes, landslides and rockfalls has filled in the channel and joined Paliki (Ithaca) to the rest of the Cephalonia concealing Ithaca from us!!!

Thanks for reading and please feel free to post any questions or comments!

References:

Odysseus Unbound: http://www.odysseus-unbound.org/

Underhill, J. (2009). Relocating Odysseus’ homeland Nature Geoscience, 2 (7), 455-458 DOI: 10.1038/ngeo562

Note: This is a repost from my pre-EGU blog location with minor updates. It was originally posted in June 2012.

Guest Post: Dr. John W. Jamieson – Using seafloor mapping to find missing Malaysia Airlines flight MH 370

Matt Herod June 16, 2014

Figure 1: Global seafloor topography map derived from satellite altimetry data. Source: http://topex.ucsd.edu/WWW_html/mar_grav.html

On March 8^th, 2014, Malaysia Airlines flight MH370 disappeared while en route from Kuala Lumpur to Beijing. Evidence from satellite tracking suggests that the aircraft may have crashed into the Indian Ocean several 1,000 kms west of Australia and this is where the search is now focused. No debris or oil slick related to the aircraft has so far been found. However, signals consistent with the “pings” of the flight data recorder were detected in two areas, several 100 kms apart from each other. A search of the northernmost location, using an autonomous underwater vehicle (AUV) owned and operated by the United States Navy has so far turned up no sign of wreckage of the aircraft. The intent of this blog post is to explain what instruments are being used to locate the wreckage, how they work, what are their limitations, and hopefully provide some clarity and perspective on the monumentally difficult task that lies ahead for the searchers.

Why is finding something on the seafloor so difficult? The methods we use for mapping and surveying on dry land (e.g., aerial photographs, satellite imagery, laser and radar mapping) rely on the electromagnetic spectrum (e.g., radio frequencies, the visible spectrum and even infrared photography). Electromagnetic waves attenuate quickly in seawater, however, and can only propagate over short distances (sunlight only penetrates the top 200 m of the ocean, known as the photic zone). The result is is that we cannot see through water very well using electromagnetic waves, and the oceans effectively shield us from surveying the seafloor using traditional means used on land (and on other planets!). So, to map the seafloor, alternative techniques are required.

On any world map that includes information on the ocean floor (e.g., Google Earth^TM) you can see features such as ridges, seamounts, the continental shelves and submarine trenches. These features were mapped using satellite altimetry, a technique in which orbiting satellites use radar to measure small spatial variations in sea level. The uneven surface of the ocean results from variations in Earth’s gravitational field, which is stronger above positive features (e.g., a volcano) on the seafloor, due to the presence of more mass, relative to regular abyssal plain. The increased gravitational pull causes seawater to preferentially flow to that location, resulting in an elevated ocean surface height directly above the volcano, or a dip in ocean surface height above a trench. These sea surface variations can be translated into a map of topographic features on the seafloor (Fig. 1). The resolution of the map, however, is only 1-3 km, which means features on the seafloor smaller than a few kilometers cannot be resolved (note that most media outlets covering the Malaysia Airlines search have been inaccurately reporting the resolution as 20 km).

Figure 1: Global seafloor topography map derived from satellite altimetry data. Source: http://topex.ucsd.edu/WWW_html/mar_grav.html

To generate maps of the seafloor with higher resolution, hydroacoustic or SONAR (Sound Navigation And Ranging) methods are used. Unlike visible light or radio waves, sound waves are compression waves and can travel greater distances in water, and hydroacoustic techniques (e.g., the “pinging” of a flight data recorder) are the standard methods used for underwater mapping and communication. Multibeam sonar is a mapping technique where a series of acoustic beams are emitted simultaneously downward to the seafloor in a fan-shaped geometry perpendicular to the direction of travel of a ship, submarine or other carrier platform. The time taken for the acoustic signals to reflect off the seafloor back to a receiver is converted into a depth. By using multiple beams, a swath underneath the ship that is roughly equally to 2 to 7 times the depth can be mapped, producing a 3-D topographic image of the seafloor beneath a vessel as it moves forward. Modern multibeam systems can produce maps with a resolution of ~30 m (actual resolution is dependent on several parameters including depth and speed of the vessel). It would take a fleet of 10 ships 15 to 45 years of continuous surveying to map the entire ocean floor at a resolution of ~40 m. Although the resolution of multibeam mapping is significantly higher than the global satellite map, it is still inadequate to be of any use for finding a downed aircraft.

Higher resolution maps can be generated if the multibeam transmitter and receiver are closer to the seafloor. This is achieved by mounting multibeam systems onto instruments towed deep beneath a ship by a cable, or, more recently, using AUVs such as the U.S. Navy’s Bluefin-21, which are effectively underwater drones that can be programmed to fly at prescribed altitudes above the seafloor. From heights of 50-100 m above the seafloor, resolutions of less than 1 m can be achieved, which is good enough to find objects on the seafloor such as sunken ships, containers that have fallen off cargo ships, or aircraft wreckage (Fig. 2).

Figure 2: Example of a 2 m resolution image of the seafloor, derived from autonomous underwater vehicle (AUV) multi-beam SONAR data. This image is from the Juan de Fuca Ridge, in the NE Pacific Ocean. The mound in the foreground has a diameter of ~75m and a height of 26 m.

A related hydroacoustic method that is commonly used (including for the Malaysia Airlines search) is side scan sonar. Instead of emitting acoustic beams downwards, beams are emitted outward and downward at a wider angle, relative to multibeam sonar. The intensity of the reflected signal is measured, producing an acoustic “image” of the seafloor. The advantage of side scan sonar is that hard, solid objects stand out clearly, and, because the survey “swath” is wider than that for a multibeam survey, a larger area can be covered.

The initial search area for MH370 was a 314 km² area where a pinging consistent with that of the Boeing 777’s black box was detected. This area was surveyed with a U.S. Navy Bluefin-21 AUV using side-scan sonar, covering an area of ~40 km² per day. This initial survey turned up no evidence of the missing aircraft. As the search radius expands, the area of seafloor to be covered increases exponentially. For example, expanding the survey area to cover 60,000 km² of seafloor, which is likely the next step, would take over two years with a single AUV. However, this area will first be mapped using ship-based multibeam (a process that has already started), before choosing new targets to survey more thoroughly with an AUV.

In 2009, Air France flight AF447 crashed in the Atlantic Ocean en route from Rio de Janeiro to Paris. The wreckage of the aircraft, including the flight data recorder, was found two years later after searching nearly 17,000 km² with 3 REMUS6000-type AUVs (one from GEOMAR in Kiel, Germany, and two from Woods Hole Oceanographic Institution, in Massachusetts, USA). Figure 3 shows side scan reflections that were the first images of wreckage on the seafloor from the Air France flight. Luckily, the wreckage came to rest in a flat, featureless area within a very mountainous region of seafloor near the Mid-Atlantic Ridge, so that the reflections seen in the image stood out easily. Had the wreckage come to rest in an area such as that shown in Figure 2, the wreckage would not necessarily stand out so clearly.

Figure 3: Side scan image of initial discovery of Air France 447. The debris appears as bright reflections on an otherwise flat seafloor. Source: http://www.bea.aero/docspa/2009/f-cp090601e3.en/pdf/f-cp090601e3.en.pdf

A major difference with the Air France search, compared to the Malaysia Airlines search, is that floating debris was discovered within a week of the crash, providing searchers a clear target from which to base their search. The current search location in the Indian Ocean is constrained by satellite data, which defines a broad area spanning 1,000s of kms, and two separate reports of potential acoustic flight recorder pings, spaced 100 kms from each other. With no physical sign of any wreckage, this search is indeed daunting and may take many years.

About the author:

John Jamieson is a research scientist at GEOMAR – Helmholtz Centre for Ocean Research, in Kiel, Germany. John obtained his B.Sc. in geology from the University of Alberta in 2002, his M.Sc. in isotope geochemistry from the University of Maryland in 2005, and his Ph.D. in marine geology from the University of Ottawa in 2013. John specializes in the study of mineral deposits that form at hydrothermal vents (or “black smokers”) on the seafloor, and the development of technology and methods for submarine exploration. His research has led to participation on several research cruises and projects in the Pacific, Atlantic and Indian Oceans. He has twice dived in the ALVIN submersible on the Juan de Fuca Ridge in the NW Pacific to depths of over 2,000 m. His research currently focuses on the use of autonomous and remotely-operated vehicles and their mapping capabilities to locate and understand the geological controls on the formation of mineral deposits on mid-ocean ridges. He works with governments, international organizations and industry on aspects related to seafloor mining.

The author, on board the French research vessel Pourquoi Pas?, with the GEOMAR REMUS6000-class AUV “Abyss” which was used in the search for the Air France flight AF447 wreckage.

GeoPoll # 2 – What geologic attraction would you like to see most?

Matt Herod May 26, 2014

The first geopoll was a huge success!! I was completely floored by the overwhelming number of responses and the time and care people took to give their opinion. The results of the last poll showed, overwhelmingly, that field work is of paramount importance to a good geology education. In fact, the top two choices with 160 and 157 votes apiece both involved taking students to the field. The third place choice was: an exposure to a wide variety of geologic disciplines. Clearly, the geoscience community is very aware of the integrated nature of our science and the importance of universities producing well rounded geoscientists that take a holistic view of problems. Finally, beer got 76 votes as an indispensable part of geology.

Sad, but true. (Glacial Till Blog)

For poll number two we enter the field. When I travel I always love to go places that offer attractions of the geologic kind as well. I have been lucky to have visited several places on this list and I think going to places and understanding how they formed and their unique geologic history is a very enriching experience and makes the trip even better. Most geoscientists that I speak to have a list of places that they want to go. So that is the question for this poll. Which geologic attraction is highest on your list to visit.

The Grand Canyon from the South Rim (Photo: Wikimedia Commons by Roger Bolsius)

Obviously, I can’t include them all so feel free to add yours in the comment box and I’ll do my best to add it as an option in the poll. Or, if you’d like to debate the merits of your choice back it up in the comments. To see the way the winds of choice are blowing click the view results link at the bottom of the poll. By the way, you only get to vote once on this one so make it count!

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GeoPoll # 1 – What does a geology education need?

Matt Herod May 5, 2014

I’d like to inaugurate a new series of posts, that will pop up on a semi-regular basis, namely, whenever I feel like it. Since day 1 of this blog, even way back in my pre-EGU days, I have tried to encourage participation from readers. To date, the only way for you to engage with me is to comment. However, in reality, not that many people are so moved that they feel like responding directly. Certainly, the proportion of readers to commenters is easily around 100:1, if not more when you take comments from family members out (haha, kidding).

Picard Engage - IT's TIME TO ENGAGE!

Therefore, to try and encourage involvement and hopefully even spur some discussion from time to time I’ll be posting a poll every so often. The plan is that I’ll write the question. It could be serious or humorous or even a bit of both. Question and answer suggestions are very welcome. I’ll also post a variety of answers that ideally will cover a range of opinions. Hopefully, with these informal opinion polls we can generate some interesting discussions and see how people feel about issues that geologists care about. The first test of the poll system a few weeks ago in my post about vadose zone modelling generated over 30 responses, so I am going to call that a success and continue polling.

This weeks poll to kick things off concerns a topic that every geoscientist should have an opinion on. Namely, what key items are necessary for a good geology education? My personal undergrad geology experience included almost all of these things and certainly lots of number 3. However, that does not mean they are truly integral to producing a geologist. Indeed, what could be dropped from a geoscience education without compromising the quality of education and what could not?

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Just a minor note, click the “view results” button on the poll to see how everyone is voting, and if you would like to add a response you can do so in the “other” box or in the comment section to start some more in depth discussion on the topic.

Happy opining!

Matt