Can freezing temperatures cause chalk to fragment?
Chalk cannot at given conditions explode chemically, spontaneously turning into other compounds.
It could locally &quot;explode&quot; mechanically as consequence of mechanical stress caused by thermal dilation due changes to temperature. But calling it explosion would be very much exaggerated. It would be rather just cracking.
There is a way such cracking would be more probable, if the chalk is porous, soaked by water. The internally forming expanding ice could crack the chalk easily  But it would not happen at the first freezing event. It would need probably repeated freezing and melting, similarly like long term freeze weathering of rocks. The speed of such process depends on porosity..
Note that such cracking would be rather progressive than sudden, with cracks or crevices developing progressively, with occasional small pieces or blocks  falling away. Sudden break of the whole block into small pieces is highly non-probable