A stock exchange crash is defined as a sudden and precipitous drop in share values. In practice it involves a drop of more than a fifth of the index within a few days.

On the 25th anniversary of the 1987 global stock market crash, below is a reminder of the major crashes since that of 1929:

- 1929: Crash on Wall Street. On Thursday, 24 October, the Dow Jones index loses more than 22 percent of its value at the opening of the session, but recoups ground to finish 2.1 percent down.

It again falls by 13 percent on 28 October and by 12 percent on the 29th. This crisis stokes speculation on the stock markets and marks the beginning of the Great Depression in the United States and a world economic crisis.

- 1987: On 19 October, Wall Street crashes. As a result of a large trade deficit in the US and a hike of interest rates by the German Central Bank, the Dow Jones index loses 22.6 percent in a single day. Other stock exchanges around the world follow suit.

It is the first crash of the information technology era.

- 1998: A crash in Russia. In August, the ruble loses 60 percent of its value in the space of 11 days, including 17.13 percent on the 27th. Russia goes through an economic and monetary crisis, in part linked to the Asian financial crisis in 1997.

In the US, the Long Term Capital Management (LTCM) hedge fund is rescued by US Federal Reserve after suffering crippling losses on highly speculative investments following the Asian financial crisis.

The Fed argues that an LTCM collapse could trigger a bust in global financial markets and hurt the US economy.

On page Two... The worst crashes of the 2000s...