Etymology

There are fairly good grounds to assume a PGmc wk. 1 *waltjan-, represented by Go waltjan ‘to beat into, roll’, OIcel velta ‘to roll, set rolling; (reflex.) turn oneself, rotate, descend’, OHG welzen ‘to roll’, OE (late WS) (ge)wyltan, (Angl.) -wæltan (etc.; see e.g. DOE s.v. āwyltan) ‘to roll’.  Evidence for a common Gmc str. v. (on which *waltjan- would be the causative) is thinner: ON had a well established str. III form, cp. OIcel velta ‘to roll, roll over; turn out, happen’, but there are no clear reflexes of this elsewhere. The ME past. walt- can be explained as wk., i.e. as a reflex of OE (Angl.) wæltan (and the pp. <-walt> (see ouerwalt) is almost certainly wk.), whose causative sense it appears to continue in Gaw and this is how it is usually understood (so OED, MED, TGD, GDS (and for ME (WM) /a/ < the Angl. i-mutation product of OE /a/ before /l/ + consonant see e.g. Jordan-Crook §62)).  On the other hand, ON input is generally allowed when it comes to ME forms with pres. welt-, which are listed as separate lexemes (with past. welt-) by OED and MED although their recorded senses overlap considerably with ME walt- and it is quite plausible that the ME past. in /a/ derives partly from the ON str. pret. valt of velta (thus perhaps Morris and Kullnick 18).

PGmc Ancestor

*waltjan-

Proposed ON Etymon (OIcel representative)

velta ‘to roll, roll over; turn out, happen’; velta ‘to roll, set rolling; (reflex.) turn oneself, rotate, descend’ 
(ONP velta (2) (vb.) and (3) (vb.))

Other Scandinavian Reflexes

Icel velta, Norw velta, OSw vælta; Far velta, Icel velta, Norw velta, Dan vælte, Sw välta

OE Cognate

 (late WS) (ge)wyltan, (Angl.) -wæltan 'to roll'

Phonological and morphological markers

Summary category

CCC2c

Attestation

Almost all citations in MED come from later ME (N and E) alliterative verse (the exceptions being a1225(?a1200) Trin.Hom.(Trin-C B.14.52) and c1450 Mandev.(4) (CovCRO Acc.325/1)). Predominantly N and Sc. in MnE dial (see EDD s.v. walt v. for attestations from Flt. and Suf.) 

Occurrences in the Gersum Corpus

Gaw 1336; Pe 1156; Cl 501; Pat 115

It is usual to find welten and walten listed as separated lexemes, but see etymological discussion.

Bibliography

MED walten (v.) , OED walt (v.) , HTOED , EDD walt v. and sb., EDD welt v.2, Dance walt, de Vries velta (1) and (2), Mag. velta (2) and (3), Bj-L. velte, Seebold walt-a-; welt-a-, Orel *weltanan ~ *waltanan; *waltjanan, AEW wieltan