Mirages

Good mirages are rare in these latitudes, especially with our cool climate. But at Jakkalsfontein there is, as we know, often more than meets the eye.


Mirage from Dassen Isalnd

When the sun was low over the island, the dark haze gradually faded and disappeared. Small thunder clouds were building up in the northwest, and we hoped for rain. Good mirages are rare in these latitudes, especially with our cool climate. But at Jakkalsfontein there is, as we know, often more than meets the eye.

Sunday 14 February 1999 was windless and warm. In Cape Town it was Valentine’s Day. Over the Groene Kloof hills on the Eastern horizon hung the grey heat haze of a proper summer’s Sunday. The beach lay unusually clear, without its customary haze, to Yzerfontein in the North and Grotto Bay in the South, where you could pick out the individual houses without binoculars. Beyond Grotto Bay stood Table Mountain, bigger than usual and with the clean look and sharply defined outline that is normally associated with an impending change in the weather. The sea reflected a bright blue sky, and the waves on the beach were low, slow and lazy. Above the western horizon hung a narrow purple bank like ships’ smoke, that stayed through the morning and into the heat of the day. That was also unusual. At about twelve o’clock we saw the amazing mirage rise over Dassen Island.

Now, what is a mirage? I have seen a line of gemsbok marching in the sky in the Namib Desert, and palm trees hanging above the sea fourteen miles east of Mombasa, but must call on specialists to explain this abnormal, very interesting and always spectacular natural phenomenon. So, to the dictionaries we go:

mirage, mïräsh’ n.: an appearance of objects raised or depressed, erect or inverted, single or double, owing to the varying refractive index of hot and cold air, the sky often simulating the appearance of water. [Fr. mirer: to look at ; L. mirari: to wonder at] (Chamber's Twentieth Century Dictionary. London, 1954.

mirage: an optical illusion caused by the refraction of light by the atmosphere, particularly in hot deserts, when the layer of air near the ground is greatly heated by conduction, hence becomes less dense, so that rays of light from the sky may be bent upwards, thus the sky may be seen by refraction, giving the impression of a shimmering sheet of water. A mirage seen over a road surface on a hot day, is known as an inferior mirage. In a superior mirage, where the light rays are bent down from a warm layer of air which is resting on a cold one, a sharply defined double or inverted image of a distant object may be seen. [F J Monk house: A Dictionary of Geography. London, 1970.]

Over the whole length of Dassen Island an image, clear as glass, of the island with its lighthouse, buildings and boulders rose and hung in the sky, barely touching the originals below and giving them the appearance of double-storied structures. The white foam of waves breaking on the south side of the island, doubled and almost tripled in height, the multiple images stacked one above the other like the sails of a ship. The whole scene, swollen to double its size, appeared bigger and much closer than before. Where it touched the purple line above the horizon, the uppermost edge of the image blurred and flickered faintly. I did not have a camera, but made the following simple sketch:

The mirage stayed for an hour and a half and then faded and disappeared, and we saw the island far away and small again, but still surprisingly clearly. By four o’clock the sun was slipping away to the west, aiming to set behind the island. About that time the purple line that hung over the horizon turned brown like heavy smoke, seemed to solidify over the length of the island, dark stalactites drooped down towards the land, and suddenly there was a perfect mirror image of Dassen Island with its lighthouse, boulders and buildings suspended upside down above its original. The huge, inverted image hung there for a long time, fading in places, getting more dense in others, stretching, shrinking, and then again hanging unmoving and heavy in the heat. The details of the image were not very clear. You could not, for instance, see the bands of colour around the upside-down lighthouse, but the outlines and the dimensions and proportions were almost perfect.

When the sun was low over the island, the dark haze gradually faded and disappeared. Small thunder clouds were building up in the northwest, and we hoped for rain. Good mirages are rare in these latitudes, especially with our cool climate. But at Jakkalsfontein there is, as we know, often more than meets the eye.

Over the whole length of Dassen Island an image, clear as glass, of the island with its lighthouse, buildings and boulders rose and hung in the sky, barely touching the originals below and giving them the appearance of double-storied structures. The white foam of waves breaking on the south side of the island, doubled and almost tripled in height, the multiple images stacked one above the other like the sails of a ship. The whole scene, swollen to double its size, appeared bigger and much closer than before. Where it touched the purple line above the horizon, the uppermost edge of the image blurred and flickered faintly. I did not have a camera, but made the following simple sketch:

The mirage stayed for an hour and a half and then faded and disappeared, and we saw the island far away and small again, but still surprisingly clearly. By four o’clock the sun was slipping away to the west, aiming to set behind the island. About that time the purple line that hung over the horizon turned brown like heavy smoke, seemed to solidify over the length of the island, dark stalactites drooped down towards the land, and suddenly there was a perfect mirror image of Dassen Island with its lighthouse, boulders and buildings suspended upside down above its original. The huge, inverted image hung there for a long time, fading in places, getting more dense in others, stretching, shrinking, and then again hanging unmoving and heavy in the heat. The details of the image were not very clear. You could not, for instance, see the bands of colour around the upside-down lighthouse, but the outlines and the dimensions and proportions were almost perfect.

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DASSEN ISLAND
Co-ordinates

YESTERYEAR
A short history of Dassen Island

MIRAGES
Good mirages are rare in these latitudes, especially with our cool climate. But at Jakkalsfontein there is, as we know, often more than meets the eye.

OIL SPILL
Jakkalsfontein staff and home owners were actively involved in assisting Cape Nature Conservation and Marine and Coastal Management with part of the biggest ever operation to save those birds unaffected by the oil, and to rescue the oiled ones.

ENVIRONMENT OF DASSEN ISLAND


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