Magma Snakes Its Way to the Sea
The Maruko Coast is extremely rocky, and there are no rest areas or other facilities to welcome tourists, yet it is well worth a visit. Though difficult to reach on foot, it is a wondrous illustration of ancient geologic activity in these islands.
Snakes in Granite
In several places you can see where long, narrow snakes of dykes (mostly basalt) have intruded themselves into blocks of granite. Finding basaltic dykes that have intruded in sedimentary deposits such as sandstone or mudstone is not so unusual, but here we can see examples of dykes having intruded into another igneous rock, granite.
In some places, the long, thin line of grey basalt now stands alone, a rope twisting toward the sea, because the granite around it has been washed away by erosion, and in other places you can see the invading black basalt “snake” settled right in the middle of the host granite.
Rocks Burned Black
Where the hot lava has intruded, it has usually burned the original granite and left clear signs of that fiery contact. In some cases, it has recrystallized the original rock, creating what are called hornfels, a phenomenon in which a cooler base rock (usually sedimentary) comes into contact with a hot, igneous material, such as basaltic magma, and the intense heat creates a new version of the original base rock.
If you have any interest in seeing unusual formations that show the amazing and unexpected power of geologic events, it is well worth taking a hike along the beach to explore the Maruko Coast.