el ps , ▁entra ined ▁air ▁b ub bles ▁in ▁the ▁bore ▁roll er , ▁sed iment ▁er os ion ▁beneath ▁the ▁bore ▁front ▁and ▁of ▁the ▁banks , ▁sc our ing ▁of ▁sho als ▁and ▁bars , ▁and ▁impact s ▁on ▁obst acles . ▁The ▁bore ▁r umble ▁is ▁heard ▁far ▁away ▁because ▁its ▁low ▁frequencies ▁can ▁travel ▁over ▁long ▁distances . ▁The ▁low - fre quency ▁sound ▁is ▁a ▁characteristic ▁feature ▁of ▁the ▁adv ancing ▁roll er ▁in ▁which ▁the ▁air ▁b ub bles ▁entra pped ▁in ▁the ▁large - scale ▁ed d ies ▁are ▁ac oust ically ▁active ▁and ▁play ▁the ▁dominant ▁role ▁in ▁the ▁r umble - sound ▁generation . ▁ ▁Et ym ology ▁The ▁word ▁bore ▁der ives ▁through ▁Old ▁English ▁from ▁the ▁Old ▁Nor se ▁word ▁b ára , ▁meaning ▁" wave " ▁or ▁" sw ell ." ▁ ▁Effect s ▁T idal ▁b ores ▁can ▁be ▁dangerous . ▁C ertain ▁rivers ▁such ▁as ▁the ▁Seine ▁in ▁France , ▁the ▁Pet it cod iac ▁River ▁in ▁Canada , ▁and ▁the ▁Colorado ▁River ▁in ▁Mexico ▁to ▁name ▁a ▁few , ▁have ▁had ▁a ▁sin ister ▁reputation ▁in ▁association ▁with ▁tid al ▁b ores . ▁In ▁China , ▁despite ▁warning ▁signs ▁ere cted ▁along ▁the ▁banks ▁of ▁the ▁Q i ant ang ▁River , ▁a ▁number ▁of ▁fatal ities ▁occur ▁each ▁year ▁by ▁people ▁who ▁take ▁too ▁much ▁risk ▁with ▁the ▁bore . ▁The ▁tid al ▁b ores ▁affect ▁the ▁sh ipping ▁and ▁navigation ▁in ▁the ▁est u ar