I did a quick look through my records and did not find any info on Alva. I did check "The Hazen Family in America" and found the information you referenced. I quick look at the 1860 census indicated that there were 6 male Hazens' in Clayton county Iowa and 1 Carpenter who all listed their birthplace as Vermont. I would also check the 1850 census for Carpenters' and Hazens' and see what you find, its possible there will be close relatives that might give a lead. The 1840 Iowa census would also be of interest to see if Alva followed some family to Iowa. Although the 1840 census will not give as much info as the 1850 and beyond. Church records in the Clayton County area would also be of interest. Census and church records can usually be found at local libraries or the Church of Later Day Saints.