Gateway of India
This Earth Cache is located on reclaimed land in the Colaba district of Mumbai in India at the edge of the harbor. I have been here a number of times and thought an Earth Cache would be an appropriate and interesting addition to this gateway. No need to access the actual Gateway, you will just need to have a clear view of the structure.
History
The Gateway of India is a very unique landmark in Mumbai and is known worldwide. The large gateway was designed by noted architect George Wittet in 1919 and completed in 1924 after 4 years of construction. The monument was designed to commemorate the visit to Bombay of King George V and Queen Mary. The gateway overlooks the harbor of Mumbai which exits out into the Arabian Sea. When built, the gateway was representative of the British colonial rule of India. The monument cost the government of India 21 lakhs at that time. The passing of the 'First Battalion of the Somerset Light Infantry' was recorded as the first main event that took place at the Gateway of India. This ceremony was conducted on February 28, 1948, when the last set of British troops and divisions left India, post-independence.
Geology
The Gateway of India monument is made of basalt along with reinforced concrete. Basalt, in general, is a volcanic rock (igneous) formed when magma near the earth’s surface cools rapidly. The word "basalt" is derived from the Late Latin “basalts”, meaning "very hard stone.” The modern term basalt describing a particular composition of lava-derived rock originates from its use by Georgius Agricola in 1556 in his famous work of mining and mineralogy De re metallica, libri XII. Agricola applied "basalt" to the volcanic black rock of the Schloßberg (local castle hill) at Stolpen in Saxony, Germany, believing it to be the same as Pliny the Elder's "very hard stone". 
Basalt is an “aphanitic” igneous rock which means it is a fine grained rock whose crystals are not detectable by the naked eye. Basalt is also considered a mafic silicate rock. Among other characteristics, mafic minerals and rocks are generally dark in color and high in specific gravity. This is in large part due to the amount of iron, magnesium, and several other relatively heavy elements which "contaminate" the silica and oxygen. Basalt contains less than 20% quartz and 10% feldspar. Basalt is one of the most common rock types in the world. Most of the ocean floor around the world is made up of basalt. Additionally, many volcanic islands, especially where the crust is thin, are also made up primarily of basalt. However, the largest volumes of basalt on land correspond to “continental flood” basalts. One of the main continental flood basalt formations are the Deccan Traps in India. Flood basalt formations occur when tremendously large volumes of molten lava accumulated outside the earth’s crust. The Deccan Traps are a large igneous province located on the Deccan Plateau of west-central India and is one of the largest volcanic features on Earth.
The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai). They consist of multiple layers of solidified flood basalt that together are more than 2,000m thick and cover an area of 500,000 km2 and a volume of 512,000 km3. The term "trap", used in geology for such rock formations, is derived from the Swedish word for stairs and refers to the step-like hills forming the landscape of the region.
The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period. This series of eruptions may have lasted less than 30,000 years in total. The original area covered by the lava flows is estimated to have been as large as 1.5 million km², approximately half the size of modern India. The Deccan Traps region was reduced to its current size by erosion and plate tectonics. Basalt is used for a wide variety of purposes. It is most commonly crushed for use as an aggregate in construction projects. Crushed basalt is used for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, filter stone in drain fields and may other purposes. Basalt is also cut into dimension stone. Thin slabs of basalt are cut and sometimes polished for use as floor tiles, building veneer, monuments and other stone objects. Typically, basalt is grey to black in color and can weather rapidly to brown or rust red due to the high levels of iron rich minerals in it. Being dense, hard and durable, the basalt from the Deccan Traps are used fairly extensively as building stones in the areas in which they occur in large masses. But, being dark in color, they are not used to the extent to which their durability would suggest. A type of basalt quarried near Mumbai is known locally as Kharodi basalt. Kharodi basalt has a useful characteristic which makes it a good candidate for monuments in a city such as Mumbai. Relative to most common igneous rocks, Kharodi basalt compositions are rich in MgO and CaO and low in SiO2 and the alkali oxides. Basalt generally has a general composition of:
- SiO2 – 45–52%
- FeO – 5-14%
- Al2O3 – 14+%
- TiO2 – 0.5–2.0%
- CaO – ~10%
- MgO – 5-12%
- Alkalies – <5%
Due to the pollution in Mumbai, acidic rain can be an issue in the degradation of monuments and buildings. However, during chemical weathering Kharodi basalt, due to its mineral content, releases readily water-soluble cations such as calcium and magnesium, which gives the material a strong buffer capacity against acid rain. This characteristic helps to protect the stone from acid degradation and keeps the monument in relatively good repair. However, because of the release of these cations as well as the iron content, the weathering can cause unsightly dark stains. The light buff and cream-colored trachytic rocks, found in the Salsette Island and more precisely in the Kharodi and Malad neighborhoods north of Mumbai are generally more preferred than the typically darker rocks both due to the pleasing coloration and the protection against acidification. When describing rocks, trachytic refers to the parallel arrangement of crystals, which mark the flow of the lava when still molten. The light buff and cream-colored trachytic rocks found in the Salsette Island and more precisely in the Kharodi and Malad neighborhoods north of Mumbai are generally more preferred than the typically darker rocks both due to the pleasing coloration and the protection against acidification.
Since the building of this monument, early in the last century, the quarries from where the stone was obtained have closed and have been built over. The buildings and monuments which used the Kharodi basalt are now one of the last places in the area to see this beautiful stone.
Requirements
To claim this Earth Cache you must answer the following questions by e-mailing them to me.
- Observe the color of basalt used in this monument. Where do you think this stone was quarried and why do you think this?
- Observe the top most row of stones above the arches. What is different about these stones? Why do you think this has occurred?
- (Optional) Post a picture of yourself with the Gateway in the background.
“Found It” logs without answers being sent to me in a reasonable time will be deleted!
Congratulations to Brandejs team for the First to Find!
