How does dehydration of an alcohol occur in alkaline medium? During aldol condensation reaction the aldol formed reacts further to give alkene (which is probably called enone)



I am really struggling with this part of the reaction as my textbook says nothing about the mechanism of this particular step
the medium during aldol condensation reaction is alkaline but the end product is a dehydrated product and the conversion of alcohol into alkene is dehydration. Do we need to make the medium acidic at later stage of reaction, or does some mechanism causes dehydration in alkaline medium?

Also please suggest if there is some other reaction, or examples depicting similar phenomenon that I could go through for better understanding

(I am really new to chemistry as well as to asking questions. thank you)
The commonly accepted mechanism for the base-catalysed aldol example here is that the alpha hydrogen (shown in blue on your scheme) is removed by OH- present in the reaction medium, and the negative charge on the enolate then forms the alkene by loss of OH-. This mechanism falls under the general heading of E1cB, further information on this mechanism may be found here and here 3.  

Thanks to @orthocresol for the note about this