Bitcoin has crashed. A year on from the bubble which saw its value surge to more than US$19,000, it's value has plunged by more than 80 per cent.

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It has fallen 43 per cent in the past month.

In fact, it has fallen five per cent this morning. It is falling so fast I've re-written the previous sentence three times now.

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It's almost as bad as to trying to live blog a Black Caps batting collapse.

A year ago speculative fever had taken hold. Everyone was talking about bitcoin millionaires and people they knew who had bought in early.

It rose almost 2000 per cent in 2017 sparking comparisons to the tulip bubble of the 1630s – a kind of investment mania, or mass public delusion.

And it was a bubble. It couldn't last and there are no prizes for picking it wouldn't.

But after an initial slump in February and March, it stabilised in the middle of this year - sitting at around US$6500.

Then a month ago it dived again. And this time it seems to be serious. It doesn't seem to have hit bottom yet.

There are a variety of reasons why it crashed. There are regulatory concerns, stories of market manipulation.

There are disputes within the cryptocurrency world about a "hard fork" - which is being blamed for the most recent sell-off.

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That's a digital currency version of a share split where new protocols are introduced which create spin-off currencies like Bitcoin SV and Bitcoin cash.

It all starts to get pretty complicated for non-techy people.

What has become clear in the past year is that Bitcoin is not progressing rapidly towards mainstream use.

In fact, the volume of daily transactions in Bitcoin has almost halved in 12 months.

At the peak of the bubble, there were nearly 500,000 transactions being done in bitcoin every day.

As of yesterday that was more like 240,000 transactions.

It is going backwards and, regardless, both numbers are tiny.

More than US$5trillion worth of traditional currencies are traded on foreign exchange markets every day.

If you think about how many individual transactions are made with traditional currency - starting with your morning coffee - the numbers are mind-boggling.

Bitcoin and its peers are still nowhere near mainstream adoption as currencies.

Which means they remain purely speculative investments.

Meanwhile, central banks and traditional trading banks are investing in the research and technology to put their own versions of digital currencies in place if and when they feel they are needed.

In it's 10-year history, Bitcoin has survived bigger crashes than this - in percentage terms at least.

Hardcore cryptocurrency believers aren't likely to be deterred by the current downturn.

But sceptics - like prominent US economist Nouriel Roubini, who has described cryptocurrency as "the mother of all scams" - see it as a reckoning.