Why are there giant concrete tunnels in the desert?

Hi @Physics Girl team! Thumbs up from me !Thanks for the video 

 Interesting point...The term gravity ...I think...is a misnomer. Gravity is an unproven theory. It does not work within any algebraic formula. It can  NOT be used as Force in any equation.  Matter bends spacetime, and the effect of that bending of spacetime is to create a generalized kind of force that acts on objects. However, it isn't a force as such that acts on the object, but rather just the 
object following its geodesic path through spacetime.
When light passes through an electromagnetic field, it is split into different spectral lines. That electrical phenomenon is what astronomers mistake for gravitational redshift. 

Electromagnetics ,on the other hand,are the only force that exists,and can be defined in realtime computational modeling. We are pushed onto earth by the electromagnetics of electrons/proton phasing , as opposed to the theory that gravity holds us to the earth the closer we are to it. An excellent example is the Saturn moon Titan.

When using surface gravity as a function of mass and radius (and sometimes speed of rotation).  Density is relevant, but it's not a complete answer. Most of the matter in the universe is in the form of plasma.
 A plasma is formed if some of the negatively charged electrons are separated from 
their host atoms in a gas, leaving the atoms with a positive charge. The negatively charged electrons, and the positively charged atoms (known as positive ions) are then free to move separately under the influence of an applied voltage or magnetic field. Their net movement constitutes an electrical current. This can explain why gravitational computation shows  (*gravity* misnomer) is stronger on the mountain peaks of the moon Titan,and much weaker in the lower valleys of Titan.