lee wrote on Sep 1
st, 2016 at 2:04pm:
... NASA says that the ice is melting from below?...
Water is melting at the top forming lakes and flowing through fissures to the bottom of the icebergs where it acts as a lubricant. Furthermore, water is heavier than ice and therefore the water column exerts a pressure at the bottom greater than that from the weight of the iceberg. This has positive feedback as the higher pressure melts the ice base. This article on relegation exemplifies the melting of ice under pressure:
https://en.wikipedia.org/wiki/Regelation Quote:Regelation is the phenomenon of melting under pressure and freezing again when the pressure is reduced. Many sources state that regelation can be demonstrated by looping a fine wire around a block of ice, with a heavy weight attached to it. The pressure exerted on the ice slowly melts it locally, permitting the wire to pass through the entire block. The wire's track will refill as soon as pressure is relieved, so the ice block will remain solid even after wire passes completely through. This experiment is possible for ice at −10 °C or cooler, and while essentially valid, the details of the process by which the wire passes through the ice are complex.[1] The phenomenon works best with high thermal conductivity materials such as copper, since latent heat of fusion from the top side needs to be transferred to the lower side to supply latent heat of melting.
If 1 mm diameter wire is used, over an ice cube 50 mm wide, the area the force is exerted on is 50 mm2. This is 50×10−6 m2.
Force (in newtons) equals pressure (in pascals) multiplied by area (in square metres).
If at least 500 atm (50 MPa) is required to melt the ice, a force of (50×106 Pa)(50×10−6 m2) = 2500 N is required, a force roughly equal to the weight of 250 kg on Earth.
Regelation was discovered by Michael Faraday. Regelation occurs only for substances, such as ice, that have the property of expanding upon freezing, for the melting points of those substances decrease with increasing external pressure. The melting point of ice falls by 0.0072 °C for each additional atm of pressure applied. For example, a pressure of 500 atmospheres is needed for ice to melt at −4 °C.[2]