Monday, January 29, 2024

Is It A Lava Tube?

My latest field geology video is about a small cave in the basalt lava near my house in Pune city. The location is Hanuman tekdi, also known as Fergusson College Hill. The cave is along the slope right behind IMDR canteen. 

Is the cave a remnant of a lava tube, or has it formed by some other process? 

Sound on. Permanent Link - Fergusson College Hill Cave.

You can access this cave by walking along the path starting from the main gate of Gokhale Institute of Politics and Economics. Turn left as you approach the hill and after a few steps look up to the right. 

Visit quickly. As you can see from this photo, rubble from the construction works of water tanks at the top of the slope is slowly spreading and might cover up this cave. I hope not. 

More geology videos soon!

Tuesday, January 16, 2024

Deep Pacific Upside Down Waterfall

This passage from Helen Czerski's Blue Machine: How The Ocean Shapes Our World gives us a glimpse of the wondrous undersea universe we are just beginning to explore.

"We see upside-down waterfalls, she says. I don't understand what she means at first, and it takes me a few seconds to process the video as Deb keep talking. In those vertical chimneys, the walls crack and hydrothermal fluids come leaking out and  you get something that looks like half a toadstool growing out of a tree in an old growth forest. And suddenly I see it. This is a gigantic hydrothermal chimney looming out of the darkness, and hot water is indeed leaking out of its side. But because hot water is less dense than cold water, the hot water keeps flowing rapidly upwards. When it first hits cold water, its clearly dumped some minerals and made a ledge that sticks out- that's the toadstool shape that Deb is referring to. The water flowing upwards has had to flow outwards underneath the ledge before it can carry on upwards. But the ledge has developed a hollow on its underside like an upside-down bowl, so there is a pool of hot water there, held in the hollow as if it were filling up the inside of an umbrella. The boundary between hot and cold water shimmers like a mirror. And then the hot water is spilling out of its hollow and continuing upwards into the gloom. It really is an upside down waterfall".

Helen Czerski is watching this footage captured by a remotely operated vehicle exploring the area around the Juan de  Fuca Ridge, an undersea mountain chain a few hundred kilometers west of Seattle. Here, the Pacific and the Juan de Fuca tectonic plates diverge. Scientists are closely monitoring this ridge for seismic and volcanic activity, using a network of sensors  called the Regional Cabled Array. Deb Kelly is the Director of this project. Hydrothermal chimneys are sulfide and carbonate mineral deposits that form when hot mineral saturated sea water emerges through cracks in the ocean crust. The are common near mid oceanic ridges where the interaction of sea water and rock heated up by magma generates vigorous hydrothermal systems.

I'm only a quarter into this book and am enjoying every page of it. Highly recommended!

Tuesday, January 9, 2024

Kenjalgad Perched Aquifer

I have been experimenting with shooting videos of geological features with an accompanying commentary. Here are two of my recent efforts.

Last month I visited Kenjalgad, a small fort near the town of Bhor. As is typical of forts of the Sahaydri ranges, it sits atop a thick basalt scarp. 

The videos explain the geological conditions for the formation of a perched aquifer. I hope I have been clear in my explanation. Sound on please! 

Kenjalgad aquifer. Location 1- Permanent Link

Kenjalgal aquifer. Location 2- Permanent Link

Kenjalgad as seen in this picture is quite an impressive mesa.

The aquifer I described in the video occurs within the topmost rock layers of the scarp forming basalt. They form discrete accumulations of groundwater high up on these ridges, separate from the aquifers underlying the surrounding valley.

I am planning on making more of these videos of various geologic features. Should they be a little longer, say two or three minutes each? I would appreciate some feedback from you.

Wednesday, January 3, 2024

The Making Of Iceland

Committees are underappreciated. 

xkcd comics.

Happy New Year everyone!