How does suddern spike in volume occurr in illquid stocks

i have noticed sertain stock volume activites will be in 1k to 2k range and suddenly 40k volume but the stock moves noware . i am qurious about i this thing coordinated ? if buyes and sellers both palce there order at same time .
it happens in lagre caps also some point of the day there will be volume of 2 to 3 lakh but stock will move noware

This is usually because of bulk/block deals.