SCIENTIST'S NOTEBOOK

                              Arenal,Costa Rica,1997

                               Arenal Volcano, in Spanish Volcán Arenal, is an active andesitic stratovolcano in north-western Costa Rica around 90 km northwest of San José, in the province of Alajuela, canton of San Carlos, and district of La Fortuna. The Arenal volcano measures at least 1,633 metres (5,358 ft).  It is conically shaped with a crater spanning 140 metres (460 ft). Geologically, Arenal is considered a young volcano and the age is estimated to be less than 7,500 years. It is also known as "Pan de Azúcar", "Canaste", "Volcan Costa Rica", "Volcan Río Frío" or "Guatusos Peak".

                                 Arenal is one of seven historically active Costa Rican volcanoes along with Poás, Irazú, Miravalles, Orosí, Rincón de la Viejacomplex, and Turrialba. It was Costa Rica's most active volcano until 2010, and one of the ten most active volcanoes in the world. It has been studied by seismologists for many years.

                                 The volcano was dormant for hundreds of years and exhibited a single crater at its summit, with minor fumaroles activity, covered by dense vegetation. In 1968 it erupted unexpectedly, destroying the small town of Tabacón. Due to the eruption three more craters were created on the western flanks but only one of them still exists today. Since October 2010, Arenal's volcanic activity appears to be decreasing and explosions have become rare, with no explosions reported between December 2010 and October 2012.

                                 The volcano is located at the center of Arenal Volcano National Park in the northern zone of the country, 15 kilometres (9.3 mi) southwest of the La Fortuna district in San Carlos (canton), Costa Rica. The temperature varies from 9 °C (48 °F) in the high areas to 89 °C (192 °F) in the low areas and the annual rainfall is around 349 centimetres (137 in).

                                 Arenal Volcano area is an important watershed for the Arenal Lake Reservoir. The reservoir's water is used for hydroelectric power. It is also connected to the national system.

                                 Arenal has a good number of eruptive vents. Chato is a dormant stratovolcanic cone. It is believed Chato first erupted 38,000 years ago during the Pleistocene period and last erupted about 3,500 years ago. Chatito 10°26′17″N 84°41′13″W is a lava dome with an elevation of 1,100 metres (3,609 ft). Espina is another lava dome.

                                Mark Twain wrote about the noises at kilauea more than ahundred years ago,and today people are still listening to volcanoes. And what they hear could save lives. Scientist Milton Garces spent a week on the slope of the Arenal volcano in the rain forest of Costa Rica,listening to explosions,hissing,and chugging sounds like those of a train. He wondered if he could use those sounds to find out what was happening inside the volcano-maybe even to help predict volcanic eruptions. 

  

PERFECT PITCH

                        Garces had become interested in volcanoes while he was studing the effect of sound under the ocean. He learned that underwater volcano hunters needed to be able to tell the noise of erupting volcanoes apart from background ocean noise. But he figured it would be easier to study volcanoes on land.He soon found that volcanoes produce a wide variety of sounds. They range from low-pitched rumbles that humans can't hear but can feel,like the passing of a jet plane,all the way up to high-pitched whines and whooshes.

                                        The rumbles are called infrasound('below sound'),and Garces found out that they are a volcano's most revealing noise. Some infrasound comes from exploding bubbles of gas and rock that propel magma and other particles into the air.Infrasound also comes from magma flow deep iside the earth. Trapped in a Bubble : Exactly what makes the rumbles? scientists think gas bubbles in streams of magma expand and contract as pressure changes. The growls they make are trapped in the magma that rises through passages that lead to the vent of a volcano. the surface of the magma acts like the head of a drum,and the sound vibrations travel through the air.

                                        Milton Garces and his colleague Michael Buckingham have collected an amazing amount of information that has helped them make models of the infrasound "fingerprint" of volcanoes. They now are sure that the amount of gas dissolved in magma determines how violent an eruption will be. In the near future,they expect to have models that translate the sounds coming from a volcano into information almost as they happen. Because a volcano can have such far-reaching effects,that's good news for all of us. But for the 500 million people living close to a volcano, it may be the difference between life and death.