"Theoretically as well as statistically, there is a very large possibility that tectonic activities trigger or increase volcanic activities," said Syamsulrizal, who works at Indonesia's national vulcanology office.

Quake activity near a dormant volcano may "switch it on," while already active volcanoes could see more intense rumblings, said the head of the office's department for disaster risk evaluation.

Since Saturday's 6.3-magnitude earthquake, seismologists have noted increased flows of lava and heat clouds at Merapi, just north of the temblor's epicentre.

Authorities had already issued a red alert ahead of a possible eruption and shelter camps were set up to house more than 24,000 people evacuated from its slopes.

Most of those have since returned home to tend flocks and crops as attention has switched to the humanitarian crisis to the south where 5,400 were killed, thousands more injured and 200,000 left homeless by the quake.

There are fears that an eruption could further devastate the area and strain the stretched quake relief effort.

"Because a volcano's activities are linked to its system of fluid dynamics, any temblor would certainly have an effect," said Gede Suwantika, who heads the quake monitoring section of the vulcanology office in Yogyakarta.

He said the high magma pressure inside the volcano could rise further as one of the two tectonic plates that meet under the Indian Ocean south of Java slides under the island, as happens in a quake.

"Statistically, this rising activity is already shown by the much higher frequency of heat clouds emitted by Merapi during the post-earthquake period," he told AFP from Yogyakarta, just 30 kilometers (20 miles) south of Merapi.

Earthquakes are caused by movements, often very slight, of parts of the earth's crust. The movements release energy and produce the shockwaves which cause the earth tremors.

Volcanic activities occur when fluid magma finds its way to the surface.

In the early hours of Tuesday, Merapi sent out 10 heat clouds and 120 lava trails, some of them two kilometers long, said Tri Yani of the vulcanology office in Yogyakarta.

Plumes of smoke were seen rising some 900 metres (3,000 feet) into the air -- nearly double the height seen the previous day.

After calming down for a few days, Merapi belched significant heat cloud torrents shortly after Saturday's temblor.

On Monday, Merapi sent out 186 lava trails and 88 heat clouds, Yani said.

Suwantika said Indonesia's volcanic and tectonic channels followed the same lines along the boundaries between different tectonic plates, perhaps explaining why Merapi would become more active following the earthquake.

Scientists have warned that the main danger posed by Merapi is the deadly heat clouds, which can travel some 100 kilometers an hour with sustained temperatures of up to 600 degrees Celsius, incinerating everything on its path.

Merapi, one of the most active of the 130 volcanoes considered dangerous across the Indonesian archipelago, killed 66 people in its last major eruption in 1994.

Its deadliest eruption in recent times occurred in 1930, when more than 1,300 people perished.

The volcano's relative period of calm last week prompted many of the 22,000 people evacuated earlier in the month to return home. Only 2,000 people remained in temporary shelters around the peak on Tuesday.

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