Blue
Grotto, also known as Il-Hnjejja ("The Arch" in Maltese), is one of
many
coastal caves found in this area. The whole system consists of six
caves, of which Blue Grotto is the largest and most impressive. It is a
stunning sea cave that was formed through
a combination of geological processes involving both marine and
tectonic activity. Here’s a detailed explanation of its formation:
Limestone Composition
Malta is predominantly composed of sedimentary rock, mainly limestone,
which was deposited in a shallow marine environment during the
Oligocene to Miocene epochs (around 23 to 34 million years ago). The
specific type of limestone found in the area of Blue Grotto is
known as Lower Coralline Limestone, which isn't a very resistant rock.
It's relatively soft and prone to
erosion.
Tectonic Activity
The central Mediterranean region, including Malta, is characterized by
significant tectonic activity due to the convergence of the African and
Eurasian plates. This tectonic activity has caused the formation of
faults and fractures in the limestone rock. Over time, these tectonic
forces uplifted parts of the seabed, creating cliffs and valleys.
Marine Erosion
The most crucial factor in the formation of the Blue Grotto is marine
erosion. The action of the sea, particularly the constant wave action
and tidal forces, eroded the limestone along the lines of weakness
created by tectonic activity. This erosion gradually carved out caves
and arches in the rock.
Solution Erosion
In addition to physical erosion by the sea, chemical weathering also
played a role. The limestone is susceptible to dissolution by acidic
seawater. Over time, the slightly acidic seawater dissolved parts of
the limestone, enlarging the caves and creating more intricate
formations.
Roof Collapse
Some sections of the caves and tunnels likely experienced roof collapse
due to the weakening of the rock by continuous erosion and dissolution.
This collapse would have further contributed to the enlargement of the
caves and the creation of openings, allowing more light to penetrate
and enhancing the blue effect for which the grotto is famous.
Blue Effect
Blue Grotto is renowned for its vivid blue color, which is a result
of the way sunlight interacts with the seawater and the white sandy
seabed. The sunlight enters the cave, reflects off the seabed, and
illuminates the water from below, giving it a striking blue hue. The
intense blue reflections in the sea are spectacularly augmented by the
orange, purple and green of the various minerals present in the rocks.
Overall, the formation of Blue Grotto is a result of a combination
of geological processes involving sedimentary rock deposition, tectonic
uplift and fracturing, and extensive marine and chemical erosion. These
processes have worked together over millions of years to create the
beautiful and iconic sea cave and arch that we see today.
Visits at Blue Grotto and the other
caves on a boat
It's possible to visit and enter into Blue Grotto and the other
caves on "Dghajjes" (small Maltese boats). The visit into the cave
isn't required for this Earthcache, but we recommended it!
For the tasks of this Earthcache you must to go at the coordinates and
observe the Blue Grotto.