In a very recent edition of New Scientist, an article Mystery cloud-like blobs over Mars baffle astronomers (16 Feb, 2015), detailed that
on 12 March 2012, amateur astronomers around the world noticed a strange blob rising out of the planet's southern hemisphere, soaring to 250 kilometres above the surface.
According to the article, this anomaly grew to be about 1000km across and even had 'fingers' stretching to space.
The article, details several theories (some being a bit wild) including atmospheric processes, aurora and stretching reality quite a bit - aliens (from the article, not me).
An image of the plume is shown below (a still image from this YouTube clip, which states that a 2nd plume was observed some months later:
The plumes appear to have formed in a region called Terra Cimmeria.
What are scientific theories, models etc for the formation of the cloud-like blobs in the Martian southern hemisphere?