Geography from the Air 1 - Dirat at Tulūl basalt plain, Syria

Background

Normally my work takes me all around the world but with the SARS/COVID-19 pandemic I'm grounded, so I fly around the world virtually instead. There are all sorts of fascinating places. If you can see the ground and know a bit of geography, you will never be bored.

Dirat at Tulūl basalt plain, Syria

Descending towards Syria's capital city of Damascus from the east, around 30 miles out, the flight path passes over a plain of lava, with a roughly circular 10 mile-wide patch of black basalt visible to the south and a line of cinder cones leading from it in a roughly north/south direction. This region located in the Rif Dimashq governate of Syria is known as Dirat at Tulūl (ديرة التلول), meaning "Land of Hills".

Descending towards Damascus from the east over the Dirat at Tulūl lava plain, looking south

Descending towards Damascus from the east, looking south

The figures below show an aerial photograph of the area (left) in natural colour and (right) overlaid by a geological map compiled by a Soviet geological survey in 1964 [1]. The red areas are recent quaternary basalts, and are surrounded by earlier quaternary basalts (lighter pink). The cinder cones lie in chains along fault lines that probably provided conduits for magma. The red dot shows very approximately the aircraft position in the above image.

The darkest area, representing the youngest lava flows, is known as the Tulul al-Safa (the Al-Safa Hills). It covers 220 square km, and contains at least 38 cinder cones, including many vents active in the Holocene (within 12,000 years). Water is extremely scarce in the Tulul al Safa, with only nomadic Bedou visiting occasionally. The inhospitibility of the region has made it a refuge, historically by the Druze in times of war. It was the last pocket of ISIL in the area, captured by the Syrian Army on 17 November 2018 in the As-Suwayda offensive.

Tulul Al Safa volcanic field

Tulul Al Safa volcanic field, from the International Space Station (Public domain image)

Although called "tulul" (meaning "hills"), the elevation of the recent lava area is only modest, as these images showing hillshade (with x4 vertical emphasis, left) and overlaid with contours at 50ft intervals (right) show.

Tulul Al-Safa area showing hillshade (x4 exaggeration) Tulul Al-Safa area showing 50ft-interval contours

The area is a little reminiscent of the lava plains of Oregon and Idaho and particularly the Craters of the Moon National Park in the Snake River Plain. Those lava plains are associated with thinning of the crust and rifting due to tectonic activity (the subduction of the Pacific plate under the North American plate). In general, plate interactions can cause thinning of the crust, reducing pressure on the mantle and resulting in melting, the buoyant melt then rising within the crust. However, that alone does not account for the volume of material in larger lava fields, which also invoke a mantle plume (as in the case of the Eastern Snake River Plain, which has been associated with the Yellowstone hotspot).

In the case of the Dirat at Tulūl lava field, which is a part of the larger Ḥarrat al-Shām volcanic field, although the lava field is close to the tectonic activity associated with the development of the Red Sea and the Dead Sea Fault System, particularly north-south regional extension parallel to the plate movements acting on existing faults [2], [3]. However, chemical and isotopic analysis of the magma origins reveals that the Syrian basalts are difficult to explain by lithospheric melting, and suggests rather an association with the Afar mantle plume under Ethiopia/Yemen and the lateral transportation of material northwards [3].

The Ḥarrat al-Shām (حَرَّة ٱلشَّام) volcanic field, also known as the Black Desert, extends from Syria into Jordan and Saudi Arabia. (There are several such "Harrats" on the Arabian Plate, of which the Ḥarrat al-Shām is the largest.) The blue dotted line in the maps here show the approximate boundary of the Harrat Ash Sham Volcanic Province [4]. The plate boundary between the African Plate and the Arabian Plate is shown as the red dotted line. The Dead Sea Fault System is a strike-slip fault along the plate boundary where Arabia is moving northwards relative to Africa at around 6mm/year.

Ḥarrat al-Shām volcanic field

Ḥarrat al-Shām volcanic field

References

[1]A. A. Krasnov, V. G. Kazmin, and V. V. Kulakov, The geological map of Syria, Syrian Arab Republic Ministry of Petroleum and Mineral Resources, 2nd ed. 1986 (geology compiled 1964).
[2]Khalil M. Ibrahim, The geological framework for the Harrat Ash-Shaam Basaltic Super-Group and its volcanotectonic evolution, The Hashemite Kingdom of Jordan Minestry (sic) of Energy and Mineral Resources, Natural Resources Authority, Bulletin 25, 1983. https://www.researchgate.net/profile/Khalil-Ibrahim-2/publication/270050950_The_geological_framework_for_the_Harrat_Ash-Shaam_Basaltic_Super-Group_and_its_volcanotectonic_evolution/links/58ef75a9aca2721d4eaf24b4/The-geological-framework-for-the-Harrat-Ash-Shaam-Basaltic-Super-Group-and-its-volcanotectonic-evolution.pdf
[3](1, 2) M.-S. Krienitz, K. M. Haase, K. Mezger, and M. A. Shaikh-Mashail, Magma Genesis and Mantle Dynamics at the Harrat Ash Shamah Volcanic Field (Southern Syria), Journal of Petrology, Volume 48, Issue 8, August 2007, Pages 1513–1542. https://academic.oup.com/petrology/article/48/8/1513/1471610
[4]USGS, World Geological Maps. https://certmapper.cr.usgs.gov/data/apps/world-maps

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