1:45 PM - 3:15 PM
[O08-P21] Study of the columnar joints and research on its origin
Keywords:columnar joint, volatile component, volcanic rock
Columnar joints are regular cracks which are made in the process when magma hardens. It has various angular points not limited to a hexagon. Our school has studied about the cause of it.
A lot of columnar joints are in Izu Peninsula , Shizuoka Prefecture. We investigated the number of sides for a columnar joints at 5 location(“Okinoshima, Oyodo Koyodo, and Futo-Coast in Ito city”, “Futou-Coast in Nishiizu town” ,and “Tsumekizaki in Shimoda city” in Izu Peninsula)① ,most of the columnar joints were hexagon in all place.
In this year’s study, we decided to find the regularity and factors focusing on components of rocks including SiO2 and volatile components and external factors. (SiO2 accounts for about half of the proportion of components in the rocks.)
Also, we similarly investigated angular numbers at 2 others locations(“Shiratori-Mountain in Izunokuni city”and,“Asahi-Waterfall in Izu city” in the center of the peninsula)② besides prior 5 locations in coasts. We inquired into the type of rocks which distribute at each locations (①②) by using “geological navigation”. In conclusion, we found the rocks at 5 locations(“Okinoshima”, “ Oyodo Koyodo, “ Futo-Coast” , “Tsumekizaki,” ,and “Shiratori-Mountain”)③ were pyroxene andesite, “Futou-Coast”s’ was dacite, and “Asahi-Waterfall” s’ was pyroxene basalt.
At the research to compare the proportion of SiO2 among 7 points, we hypothesized that the higher proportion of SiO2 rocks would have larger numbers of angles. In conclusion, at the 4 locations(③except “Shiratori-Mountain”), the mode of the angler shape was hexagon. Exceptionally, in“ Shiratori-Mountain”, the mode was a square shape and composed of pyroxene andesite.
Next, we focused on differences of columnar joints between in the coast and inland. This is a guess but on the coast, cooling speed is faster because of sea water. On the contrary, in inland, the speed is slower.
Then we speculated that cooling speed affected angular numbers.
(SiO2 affects freezing point. The lower concentration rocks have causes higher freezing point and a faster cooling speed. )
Based on these factors, in inland, the mode of angular shape is square regardless of the type of rocks. In coast, rocks tend to have a lot of angular numbers, but it is related to the type of rocks.
A lot of columnar joints are in Izu Peninsula , Shizuoka Prefecture. We investigated the number of sides for a columnar joints at 5 location(“Okinoshima, Oyodo Koyodo, and Futo-Coast in Ito city”, “Futou-Coast in Nishiizu town” ,and “Tsumekizaki in Shimoda city” in Izu Peninsula)① ,most of the columnar joints were hexagon in all place.
In this year’s study, we decided to find the regularity and factors focusing on components of rocks including SiO2 and volatile components and external factors. (SiO2 accounts for about half of the proportion of components in the rocks.)
Also, we similarly investigated angular numbers at 2 others locations(“Shiratori-Mountain in Izunokuni city”and,“Asahi-Waterfall in Izu city” in the center of the peninsula)② besides prior 5 locations in coasts. We inquired into the type of rocks which distribute at each locations (①②) by using “geological navigation”. In conclusion, we found the rocks at 5 locations(“Okinoshima”, “ Oyodo Koyodo, “ Futo-Coast” , “Tsumekizaki,” ,and “Shiratori-Mountain”)③ were pyroxene andesite, “Futou-Coast”s’ was dacite, and “Asahi-Waterfall” s’ was pyroxene basalt.
At the research to compare the proportion of SiO2 among 7 points, we hypothesized that the higher proportion of SiO2 rocks would have larger numbers of angles. In conclusion, at the 4 locations(③except “Shiratori-Mountain”), the mode of the angler shape was hexagon. Exceptionally, in“ Shiratori-Mountain”, the mode was a square shape and composed of pyroxene andesite.
Next, we focused on differences of columnar joints between in the coast and inland. This is a guess but on the coast, cooling speed is faster because of sea water. On the contrary, in inland, the speed is slower.
Then we speculated that cooling speed affected angular numbers.
(SiO2 affects freezing point. The lower concentration rocks have causes higher freezing point and a faster cooling speed. )
Based on these factors, in inland, the mode of angular shape is square regardless of the type of rocks. In coast, rocks tend to have a lot of angular numbers, but it is related to the type of rocks.