The formation of Aden is purely volcanic, and bears the appearance of having been in recent activity. It is supposed that the peninsula was originally an island, and became gradually connected by the accumulation of sand in the narrow channel which intervened between it and the mainland.
The whole peninsula is a large crater, formed by lofty and precipitous hills, the highest of which, Shumshum, has an elevation of 1,755 feet, but, being entirely destitute of vegetation, looks much higher.
The range of hills which forms the wall of the crater is nearly circular: on the western side the hills are very precipitous, and the rain-water descending from them is carried rapidly to the sea; on the interior, or eastern side, the hills are quite as abrupt, but the descent is broken by a table-land occurring midway between the summit and the sea-level, which occupies about one-fourth of the entire superficies of Aden. This plateau is intersected by numerous ravines, nearly all of which converge into one valley, which thus receives the drainage of the peninsula. From the remotest times this provision of nature has been seized upon for supplying the town of Aden with water. Tanks of various dimensions, and the most fantastic shapes, have been formed, in many cases by simply building a dyke across a ravine; while they are so constructed that on the overflowing of one the water reaches the next—and thus a complete chain has been formed, reaching the heart of the town.
The annual fall of rain in Aden is very limited, seldom exceeding seven inches; and as the neighbouring country is in too unsettled a state to restore the aqueduct built by the Sultan of Yemen, Melek-el-Mansoor, towards the close of the fifteenth century, which conveyed the water of the Bir Hameed into Aden, and it having been found that increasing the number of wells does not proportionately increase the supply of water, recourse is now being had to condensing the water of the bay into fresh water.
The scarcity of water in such a climate, and at a place of such importance, both in a commercial and also a strategic light, is a matter of serious consideration, and is engaging all the energies of Brigadier Coghlan to remedy, by clearing out and repairing all the ancient tanks.
The town and the principal portion of the military cantonments are within the crater already described, and consequently they are surrounded on all sides by hills, except on the eastern face, where a gap exists opposite the fortified island of Sheerah. This inlet is called Front or East Bay.
The crater has been cleft from north to south, and the rents thus produced are called the northern and southern passes; the former, better known as the main pass, is the only entrance into the town from the interior or from the harbour.
When this town was visited by Captain Haynes, of the Indian navy, the ruin of Aden appears to have been complete. It was nothing but a wretched village, built on the ruins of the former city, containing about ninety stone houses, in a dilapidated state, and only one mosque in a state of repair. The remainder of the dwelling-places were miserable huts made of mats. Its trade was annihilated, its wells brackish from neglect, and everything bearing the mark of ruin and decay.
Since the conquest in 1839, how rapidly has it changed! A neat and well-built town has superseded the former squalid-looking village. The population has increased from 600 to 25,000; while the value of the trade, including imports and exports, amounts to upwards of one million sterling per annum.