In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
1. Zakāt will only become wajib once the savings reach the nisāb (Rs 65000). In your scenario 1, the nisāb is attained in April 2012. From April 2012 you will calculate 1 whole year and check in April 2013 whether you still have nisāb or not. If in April 2013 you have R 100,000 in your savings, which is above nisāb, then you will calculate zakat using this figure.
For your next year (i.e 2014), you will check your savings in April 2014. If you do not possess the nisāb at that time, then there will be no zakāt. 
2. If you have the savings equal to or more than the nisāb at the beginning and at the end of your zakat year (worked out on a lunar calendar), then the fluctuations during the year will not make a difference. So, if in the beginning of the year you had Rs 65,000 in savings and then lost it all by April only to regain them by June of the same year, then as long as you have nisāb by the end of the year, you will pay zakāt for the whole year. This zakāt, like the scenario 1, will be calculated according to your savings at the end of the year. 
And Allah Ta’āla Knows Best
Mufti Faisal bin Abdul Hameed,
Checked and Approved by,
Mufti Ebrahim Desai.
 (وشرط كمال النصاب) ولو سائمة (في طرفي الحول) في الابتداء للانعقاد وفي الانتهاء للوجوب (فلا يضر نقصانه بينهما) فلو هلك كله بطل الحول (الدر المختار وحاشية ابن عابدين (رد المحتار) (2/ 302))
 المرجع السابق