Roads of Arabia

02bis (08) Arabie US p54-69_BAT.qxd 23/06/10 19:37 Page 56
ROADS OF ARABIA
Geographic Introduction to the Arabian Peninsula
Fig. 1. Geomorphological map and
geological section of Arabia
Fig. 2. Average annual rainfall in Arabia
Hélène David, 2010
Hélène David, 2010
volcanic eruptions
Oman mountain
crystalline plinth
Paleogene and Neogene
]
limestone plateaux
Jurassic and Cretaceous
Palaeozoic and Triassic (sandstone plateaux)
regs of gravel and pebbles
salt flood depression
dune fields
plains and depressions (Quaternary)
paleo-drainage
wadi
escarpment bordering Tihamah
cuest and cliffs
north, in Jabal Hisma on the edge of the Gulf of Aqaba, they reach 2,681 metres and in the
south are even higher, attaining 2,000 metres, not far from Mecca in the Hijaz, 3,000
metres near Abha in the ‘Asir, and even more in Yemen, a country of high plateaus of
between 2,500 and over 3,000 metres with mountains culminating at 3,760 metres in the
Nabi Shu’ayb, not far from the capital, Sanaa. Mountains and plateaus abruptly decline
towards the Red Sea, especially in the ‘Asir and in Yemen where the valleys plunge into
impressive gorges. In the north there is only a narrow and discontinuous coastal plain,
whereas in the south the coastal region, the Tihamah, widens extensively.
In the eastern half of the peninsula a succession of sedimentary layers, more recent
from west to east, can reach considerable thicknesses. Erosion scooped out a series of
meridian depressions in the soft rock, throwing into relief escarpments and plateaus
carved in hard rock, sandstone or limestone. Thus Jabal Tuwayq, culminating at 1,500
metres, forms a vast arc of a circle over 800 kilometres long, presenting to the west a rocky
cliff over 200 metres high.
Everywhere rocky scarps are sculpted by desert erosion with very steep slopes going
down to the flat surfaces of the regs – formed of coarse sands – that surround them.
Mechanical erosion plays a major role (frost in the high or northern regions, thermoclastic
56
57