hi! Well first, assuming you're asking why didn't Russia 'discover' Alaska before Columbus, the answer is that at that point in history, Russia was nowhere near the size that it is today, and nowhere near the Bering Straight:

• Why didnt the Russians or mongols ever try to get to Alaska, or never knew about it? Until Columbus. - includes a nice map showing Russian territorial gains over time

• Why didn't Russia discover North-America first? - a few more facts & figures

• Russia is so close to Alaska, why didn't the Russians discover North America well before Columbus?

So when did Russia reach Alaska?

• Why didn't Russia discover alaska right off their eastern coast? - quick intro to Vitus Bering

• What made the Bering Straight so impassible? Did Asians really never visit Alaska after the migrations?

• When the Russians landed in Alaska, did they know that was part of the same land that the Europeans had found? When did the Europeans and Russians finally meet in North America? - a nice rundown on exploration

• To what extent did the Russians colonize Alaska? (and other Alaskan questions)

What about Siberians before (or after) Russian expansion?

• How did the first humans migrate to the Americas?

• How do we know that Siberians weren't the first to come to America after the land bridge?

• Why didn't the Russians discover The New World before The West?

• How come America was not "discovered" via the Bering Strait?

• Why weren't modern Siberians colonizing the new world prior to Europeans

.. or the other way around?

• Were Native American aware of the existence of other continents before 1492?

• Did Alaskan natives have knowledge Asian peoples in Siberia before the colonization of the Americas?

• more posts Was there trade across the Bering strait before the age of discovery?

The Siberian far-east was barely even explored by Russia until the expeditions of Vitus Bering.