Looking at nature with understanding is much more pleasing than just looking at its beauty (Albert Heim, 1878)
Indonesia is a country with the largest number of active volcanoes that is 127 active volcanoes. However, only 69 volcanoes are monitored by seismic devices which constitute the minimum standard of volcano monitoring devices  .
Volcanoes provide a very horrific picture for the people. The eruption of Mount Merapi, Yogyakarta is one example of a terrible disaster from the existence of a volcano. However, volcanoes also provide abundant natural resources such as springs, minerals and of course a very beautiful scenery when we explore it.
One of the volcanoes that are warmly discussed is Mount Ijen. Mount Ijen is located in two districts, Banyuwangi and Bondowoso districts. The beauty and uniqueness of Ijen mountain attracts many local and international tourists. From Mount Ijen, we can see volcanoes like mountains and mountains Marapi mountain.
The height of Ijen mountain is 2,443 meters above sea level and at its peak is a crater filled with acidic liquids  . Mount Ijen was formed from an ancient Ijen mountain some 700,000 years ago in a shallow marine environment  . Then, the ancient Ijen volcano erupted and collapsed which produced the caldera lake. Due to the existence of the Blawan fracture, the caldera lake becomes dry which then leaves only the crater.
In addition, on the lips of the caldera formed 5 volcanoes one of which is Ijen mountain which is now being enjoyed by many people for tourism and in the middle of the crater formed 17 mountain children. Mount Ijen last erupted in 1999  .
Figure 1. Ijen mountain formation process 
The most impressive phenomenon of Ijen volcano is the phenomenon of blue flame ( blue fire ) that only occurs in two places, the volcano in Iceland and Ijen volcano in Indonesia. This is an unusual phenomenon because volcanoes usually produce red lava and black smoke just like Mount Merapi or Mount Sinabung.
The blue flame of Ijen crater is always on all day but can only be seen at night. because during the day, the intensity of the sun (yellow) combined with the blue fire makes the blue flame we can not see clearly. The blue flame is generated from the reaction between sulfur / solid sulfur (S 8 ) with oxygen at temperatures above 300 o C which produces blue flame and SO 2 gas  . The reaction is as follows :
S 8 + 8 O 2 = 8 SO 2 (blue flame)
The sulfur solids in Ijen crater are formed by the reaction of H 2 S and SO 2 gas . Ijen crater produces SO 2 as much as 200 tons per day which potentially produces 100 tons / day of attacking solids  . H 2 S and SO 2 will be condensed first, then will react to produce sulfur and water solids (H 2 O). This natural phenomenon is adopted by several industries that produce H 2 S.
In industry, the reaction of the formation of sulfur solids of H 2 S and SO 2 is called the Claus process  . The reaction is as follows :
2H 2 S + SO 2 = 3/2 S 2 + 2 H 2 O
Because SO 2 and H 2 S gas are very dangerous for humans, tourists visiting the crater of ijen are required to use masks and do not come closer to the crater area.
In addition, after 12 noon, tourists are advised not to be on the top of the mountain ijen because wind causes SO 2 gas will lead to where ordinary tourists take pictures or sit back. Mount Ijen also presents the activities of the sulfur miners.
We can see firsthand how the process of sulfur mining in the volcano environment. In one mine, sulfur miners are able to carry 60 to 100 kg of sulfur. Every day, sulfur miners are able to do 2 times mining.
The condensation of H 2 S and SO 2 gas is flowed through a 50 – 150 m pipeline with a total of 100 fruits which will produce a yellow – brown thick liquid which is a sulfur solid  . One thing that concerns us is a kilogram of sulfur is only valued at Rp. 680 / kg  . Of course, the price is not worth the risk that miners face every day. To increase the income, the miners create sulfuric sulfur made solid into various shapes sold at a price of Rp. 5,000 – Rp. 30.000 / souvenir.
Figure 2. Blue flame at Ijen Crater  (b) formation of sulfur solids  (c) sulfur miners (private documents)
In addition to the utilization of sulfur, Ijen crater has an abundant water source. However, the spring on the ijen mountain that flows through the river banyuputih mixed with acidic liquids from the crater. The acidic fluid in the ijen crater has a very low pH value of 0.5  . This is the main concern of local governments in managing natural resources to be utilized by surrounding communities.
Going forward, the government and other agencies will make the sprinkling of the springs channel and the acidic liquids so that only water from the springs flowing into the river. This river flow can also be utilized for micro hydro power plant (PLTMH)  .
Another potential is geothermal energy that has been explored by PT.Medco Cahaya Geothermal (MCG) since 2011. Eskplorasi is still carried out until May 2018. The potential of geothermal energy in 110mW of ijen mountain complex. PT MCG has signed a contract with PT. PLN for power purchase agreement for 30 years. The project will operate commercially in 2020 or 2021  .
Nature presents a million wisdom to the human being that grows around it. Blessing, man lives in prosperity, prosperity and peace. It is appropriate, nature and humans to synergize and respect each other for survival on earth.
Blue Fire (Blue Fire) in Ijen Crater, Indonesia 
 People’s Mind. 2012. Indonesia Has 127 Active Volcanoes . ( http://www.pikiran-rakyat.com/national/2012/05/02/186891/indonesia-miliki-127-gunung-api-aktif ) accessed on March 2, 2018
 Wikipedia Indonesia. Mount Ijen. ( https://en.wikipedia.org/wiki/Gunung_Ijen ) accessed on March 2, 2018
 Wirakusumah, AD, Murdohardono, D and Rosiani, D. 2018. Geowisata in Banyupaitih / Banyuputih Watershed Area, G.Ijen, East Java . High School of Energy and Minerals.
 Milley, J. 2018. The Mystery of Blue Lava and The Ijen Volcano Crater . ( https://interestingengineering.com/blue-lava-largest-sulfuric-acid-lake-ijen-volcano ) accessed on 2 March 2018
 Sendt, K and Haynes, BS 2005. Role of The Direct Reaction H 2 S + SO 2 in The Homogenous Claus Reaction . J. Phys Chem A, 109, 8180-8186.
 Agustinus, M. 2017. Medco Pocket Extension of Geothermal Exploration in Ijen . ( https://finance.detik.com/energi/3641482/medco-kantongi-perpanjangan-izin-eksplorasi-panas-bumi-di-ijen ) accessed on March 2, 2018
 Grunewald, O. 2015. Ijen Crater – Volcano with Glowing Blue Lava in Indonesia . (https://www.youtube.com/watch?v=82CC3reHX0g) accessed on March 2, 2018
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