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INTRODUCTION OF THE PITON DE LA FOURNAISE
The Volcano : The Piton de La Fournaise is a hawaiian type of volcano. It is 2631 meters high and has 2 main simmit crater, the Bory and the Dolomieu. It was born about a million of years ago. Some years ago a consensus was eatablished around 400 000 years, but new datas replaced these estimations and nowadays, scientists know the volcano is much older.
Dolomieu:
This volcano is a hot spot dont with fluid basaltic magma , it allows the gas to escape easily. Its eruptions usually last a few weeks. They begin with 1 or more breaks opening along hundreds of meters. Soon, the actvity installs in 1 or 2 spots with fountains of lava about 20 to 50 meters high .They can reach several hundreds of meters.
Basalt is a common gray to black volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth's surface. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black, characterized by a preponderance of calcic plagioclase feldspars and pyroxene together with minor amounts of accessory minerals such as olivine.
The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarse) groundmass should generally be referred to as dolerite or gabbro. The crustal portions of oceanic tectonic plates are predominantly made of basalt.
http://en.wikipedia.org
The hawaiian type of volcanoe like the Piton de la Fournaise provide 2 very different types of lava:
Pahoehoe :
 
Aa :
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The pahoehoe is made of smooth and folded lava named pahoehoe by volcanologists.
This curious name comes from hawaiian language and means the satin river. Indeed, when it cools off, the flowing lava gets shiny like satin.
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The aa type is characterized by rocks teared to pieces and slaggy . The big difference between the 2 types is the gas pressure and the temperature (over 1000 degrees celcius)
Pahoehoe
Toes of a pahoehoe advance across a road in Kalapana on the east rift zone of Kilauea Volcano in Hawaii.Pahoehoe (Hawaiian English, from Hawaiian, meaning "smooth, unbroken lava") is basaltic lava that has a smooth, hummocky, or ropy surface. A pahoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. The surface texture of pahoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture.
http://en.wikipedia.org
Aa (Hawaiian English, from Hawaiian meaning "stony with rough lava", but also to "burn" or "blaze") is one of three basic types of flow lava. Aa is characterized by a rough or rubbly surface composed of broken lava blocks called clinker.
The clinkery surface actually covers a massive dense core, which was the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an aa flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an aa flow. Accretionary lava balls as large as 3 m (10 ft) are common on aa flows. Aa is usually of higher viscosity than pahoehoe (usually spelled just pahoehoe). Pahoehoe can turn into aa?
if it becomes turbulent due to meeting impediments or steep slopes.
http://en.wikipedia.org
The lava flows on several kilometers ...
Climate: the weather in the volcanic area is very extreme Its direct exposition to the trade winds makes it a very rainy area. The best time to visit the volcano is during the interseasons: spring and fall when the trade winds are weaker and the tropical storms very rare.
During austral winters, from june to september when the cold fronts show up, the weather is a real nightmare and can come over the volcano in a few hours with non-stop cold rains and a violent wind around 32 F. It can even snow like it happened during 2 days in August 2003 . Fortunately the weather can be clement on the summit area and allow us to take pictures.
During the summer, new problems can occur: If the temperature is nice, the tropical storms and hurricanes destabilise the weather on the volcano as far as 600 km awa y from the island. In this case, torrential rains fall on the volcano and the average precipitations are around 200mm per day and they can be as bad as 500mm up to 1 meter !
But if yo wish to discover the volcano trekking, these datas should not discourage you, the visit of the summit crater happens in the western area where the weather is the best with 50% of good weather during the year. It is only the eastern part of the volcano where the weather gets really bad with fog and precipitations around 12 meters per year. So to visit the volcano, if you stay on the island for several days, you should plan 2 different period to do it to assure you a nice weather.
 
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