It looks like a passage into another dimension, or an alien space ship hovering just out of vision. And the people of Twitter want answers.

On Monday, images of a bizarre cloud hovering over Wonthaggi, a seaside town 132 kilometres south-east of Melbourne, saturated social media as puzzled users sought answers.

Photos of the cloud – which looks like a massive, ethereal, rainbow-filled hole splitting up a stormy sky – emerged just before 1pm on Monday after a listener called into radio station 3AW.

Soon, Wonthaggi locals began posting images of the bizarre cloud formation, asking: “What’s going on over Wonthaggi?”

Another user wanted to know if the world had reached its end: “Rapture’s here, folks. Some weird rainbow/ cloud action going on in Wonthaggi right now,” he said, tweeting another picture.

But the Bureau of Meteorology’s duty forecaster, Michael Efron, wasn’t too worried.

“It looks like a fallstreak cloud, also known as a punch hole cloud,” he told Fairfax Media.

“They form when the water temperature in the cloud is below freezing, but the water has not yet frozen due to a lack of ice nucleation particles.

“In this case, when the water does start to freeze, it falls down to the surface … so you’re left with this cloud surrounding it, this clear area.”

Mr Efron said high clouds – about 5km above ground – were needed for fallstreak clouds to form.

The rainbow inside the cloud is called “iridescence”, Mr Efron said, which most often occurs in soap bubbles, butterfly wings and sea shells.

“This type of [cloud] iridescence occurs with high level cloud and with diffraction, [meaning] that water droplets are gathering light,” Mr Efron said.

The type of effect does not occur in all clouds, which are made of condensed water vapour, he said.

Although the bureau does not keep records of the how often this cloud formation occurs, Mr Efron said a similar cloud emerged in Perth last month, shaped like a watery UFO.

The fallstreak cloud can be triggered by aircraft flying through the area, and can “persist as long as we’ve got high cloud around”, Mt Efron said.

– Independent.co.uk

– Youtube: Kang Matthew