IS Mexico about to erupt politically the way the Popocatepetl volcano ("Popo" for short) is threatening to do just 33 miles away from the capital? The metaphor is irresistible as tension builds up for tomorrow's elections, which could lead in 2000 to what one Mexican has described as the first peaceful transfer of power in 600 years.
The ruling party, the Partido Revolucionario Institucional (PRI), has been in power since 1929 under different acronyms controlling presidency, congress, Mexico City, and most of the 31 provinces - in other words, practically everything that moves.
In this election the PRI will lose Mexico City and possibly its majority in the lower house of Congress. How can that happen without some boiling lava being spewed over the political and social scene?
If you can imagine Fine Gael having been in power since the Civil War in 1922 until today and the kind of machine for patronage and corruption that would have been built up, you get some idea of what the position of the PRI is in Mexico. But while Fine Gael did the decent thing and encouraged its Fianna Fail foes to enter democratic politics and then got booted out after 10 years, the PRI decided to run everything and succeeded brilliantly.
There was no need to have an opposition. All the sectors that counted were absorbed into the PRI - the trade unions, the farming organisations, the professional classes, the bureaucrats. Needless to say, the army and the police were as "'PRI-ista" as the next. The party colours were the same as the national flag.
And Mexico prospered for much of the time with a growth rate envied by its South American neighbours and no more violent transfers of power. Elections were held regularly and the PRI just kept winning. It was rather like elections under Stalin or Mao.
The facade cracked a little in 1986 when a PRI rising star with two famous names, Cuauhtemoc Cardenas, rebelled against the system whereby the outgoing president nominated his successor for the next six years. Cardenas had not made it to the final list and set up his own party.
Today Cardenas, whose father was one of Mexico's most revered presidents in the 1930s, is poised to take revenge on the PRI by becoming the first elected mayor or governor - of Mexico City and its nine million citizens. His left-wing Partido de la Revolucion Democratica (PRD) might also win enough seats in the congressional election to deprive the PRI of its overall majority there for the first time.
Before the PRD appeared on the scene, there had been another party, the Partido Accion Nacional (PAN), which had been starting to make inroads on the PRI's control over all the 31 provinces or states. The official name for the country is the "United States of Mexico" but under PRI centralisation, the" idea of a federation had becomes a joke until PAN started winning governorships.
The PAN was deeply conservative in morals and economics and had rebelled against the corruption of the PRI and its anti-clerical tradition. PAN is at the opposite end of the spectrum from Cardenas's PRD in economic and social affairs but together they might muster enough votes in the new Congress's lower house to end PRI's long reign.
So the political volcano is rumbling alongside "Popo" which has not had a major eruption for about 1100 years but this week alarmed the capital by belching ash and gaseous vapours over an already heavily-polluted city. The peasants living on its slopes are ready for evacuation if the big one comes. Surely this is an omen for the PRI that its timed has come?
The funny thing is that President Zedillo, who became the PRI President of Mexico in 1994 after the party's first choice was mysteriously murdered, has been pushing through electoral reforms that look like ensuring that the PRI loses out to its rivals.
Wall Street stockbrokers are not alarmed at the prospect of, the PRI losing some power as long as the process is gradual. What would be more alarming for foreign investors would be an election which the PRI won by fraud and resulted in turmoil. The new independent electoral commission is virtually guaranteeing that there will be no undetected frauds in this election.
Even the loss of Mexico City and an overall majority in the lower house will not knock the PRI out of business. The party will still have the powerful presidency, the Senate and most of the governorships of the provinces. But Mexico will have taken a major step towards the kind of democracy which the Revolution of 1917 was supposed to have introduced.